Publications by authors named "Frantisek Hartl"

77 Publications

Effect of the 2-R-Allyl and Chloride Ligands on the Cathodic Paths of [Mo(η-2-R-allyl)(α-diimine)(CO)Cl] (R = H, CH; α-diimine = 6,6'-Dimethyl-2,2'-bipyridine, Bis(-tolylimino)acenaphthene).

Organometallics 2021 Jun 2;40(11):1598-1613. Epub 2021 Jun 2.

Department of Chemistry, University of Reading, Reading RG6 6DX, United Kingdom.

The new, formally Mo(II) complexes [Mo(η-2-R-allyl)(6,6'-dmbipy)(CO)Cl] (6,6'-dmbipy = 6,6'-dimethyl-2,2'-bipyridine; 2-R-allyl = allyl for R = H, 2-methallyl for R = CH) and [Mo(η-2-methallyl)(pTol-bian)(CO)Cl] (pTol-bian = bis(p-tolylimino)acenaphthene) share, in this rare case, the same structural type. The effect of the anionic π-donor ligand X (Cl vs NCS) and the 2-R-allyl substituents on the cathodic behavior was explored. Both ligands play a significant role at all stages of the reduction path. While 2e-reduced [Mo(η-allyl)(6,6'-dmbipy)(CO)] is inert when it is ECE-generated from [Mo(η-allyl)(6,6'-dmbipy)(CO)(NCS)], the Cl ligand promotes Mo-Mo dimerization by facilitating the nucleophilic attack of [Mo(η-allyl)(6,6'-dmbipy)(CO)] at the parent complex at ambient temperature. The replacement of the allyl ligand by 2-methallyl has a similar effect. The Cl/2-methallyl ligand assembly destabilizes even primary radical anions of the complex containing the strongly π-accepting pTol-Bian ligand. Under argon, the cathodic paths of [Mo(η-2-R-allyl)(6,6'-dmbipy)(CO)Cl] terminate at ambient temperature with 5-coordinate [Mo(6,6'-dmbipy)(CO)] instead of [Mo(η-2-R-allyl)(6,6'-dmbipy)(CO)], which is stabilized in chilled electrolyte. [Mo(η-allyl)(6,6'-dmbipy)(CO)] catalyzes CO reduction only when it is generated at the second cathodic wave of the parent complex, while [Mo(η-2-methallyl)(6,6'-dmbipy)(CO)] is already moderately active at the first cathodic wave. This behavior is fully consistent with absent dimerization under argon on the cyclic voltammetric time scale. The electrocatalytic generation of CO and formate is hampered by the irreversible formation of anionic tricarbonyl complexes replacing reactive [Mo(η-2-methallyl)(6,6'-dmbipy)(CO)] along the cathodic route.
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http://dx.doi.org/10.1021/acs.organomet.1c00038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8289335PMC
June 2021

Optical and Infrared Spectroelectrochemical Studies of CN-Substituted Bipyridyl Complexes of Ruthenium(II).

Inorg Chem 2021 Mar 1;60(6):3514-3523. Epub 2021 Mar 1.

School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, E1 4NS London, United Kingdom.

Ruthenium(II) polypyridyl complexes [Ru(CN-Me-bpy)(bpy)] (CN-Me-bpy = 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine, and = 1-3, abbreviated as , , and ) undergo four () or five ( and ) successive one-electron reduction steps between -1.3 and -2.75 V versus ferrocenium/ferrocene (Fc/Fc) in tetrahydrofuran. The CN-Me-bpy ligands are reduced first, with successive one-electron reductions in and being separated by 150-210 mV; reduction of the unsubstituted bpy ligand in and occurs only when all CN-Me-bpy ligands have been converted to their radical anions. Absorption spectra of the first three reduction products of each complex were measured across the UV, visible, near-IR (NIR), and mid-IR regions and interpreted with the help of density functional theory calculations. Reduction of the CN-Me-bpy ligand shifts the ν(C≡N) IR band by ca. -45 cm, enhances its intensity ∼35 times, and splits the symmetrical and antisymmetrical modes. Semireduced complexes containing two and three CN-derivatized ligands , , and show distinct ν(C≡N) features due to the presence of both CN-Me-bpy and CN-Me-bpy, confirming that each reduction is localized on a single ligand. NIR spectra of , , and exhibit a prominent band attributable to the CN-Me-bpy moiety between 6000 and 7500 cm, whereas bpy-based absorption occurs between 4500 and 6000 cm; complexes , , and also exhibit a band at ca. 3300 cm due to a CN-Me-bpy → CN-Me-bpy interligand charge-transfer transition. In the UV-vis region, the decrease of π → π* intraligand bands of the neutral ligands and the emergence of the corresponding bands of the radical anions are most diagnostic. The first reduction product of is spectroscopically similar to the lowest triplet metal-to-ligand charge-transfer excited state, which shows pronounced NIR absorption, and its ν(C≡N) IR band is shifted by -38 cm and 5-7-fold-enhanced relative to the ground state.
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http://dx.doi.org/10.1021/acs.inorgchem.0c03579DOI Listing
March 2021

Dynamic Covalent Properties of a Novel Indolo[3,2-b]carbazole Diradical.

Chemistry 2021 Mar 25;27(17):5509-5520. Epub 2021 Feb 25.

Department of Physical Chemistry, University of Málaga, Campus de Teatinos s/n, 229071, Málaga, Spain.

This work describes the synthesis and properties of a dicyanomethylene-substituted indolo[3,2-b]carbazole diradical ICz-CN. This quinoidal system dimerises almost completely to (ICz-CN) , which contains two long C(sp )-C(sp ) σ-bonds between the dicyanomethylene units. The minor open-shell ICz-CN component in the solid-state mixture was identified by EPR spectroscopy. Cyclic voltammetry and UV-visible spectroelectrochemical data, as well as comparison with reference monomer ICz-Br reveal that the nature of the one-electron oxidation of (ICz-CN) at ambient temperature and ICz-CN at elevated temperature is very similar in all these compounds due to the prevailing localization of their HOMO on the ICz backbone. The peculiar cathodic behaviour reflects the co-existence of (ICz-CN) and ICz-CN. The involvement of the dicyanomethylene groups stabilizes the close-lying LUMO and LUMO+1 of (ICz-CN) and especially ICz-CN compared to ICz-Br, resulting in a distinctive cathodic response at low overpotentials. Differently from neutral ICz-CN, its radical anion and dianion are remarkably stable under ambient conditions. The UV/Vis(-NIR) electronic transitions in parent (ICz-CN) and ICz-CN and their different redox forms have been assigned convincingly with the aid of TD-DFT calculations. The σ-bond in neutral (ICz-CN) is cleaved in solution and in the solid-state upon soft external stimuli (temperature, pressure), showing a strong chromism from light yellow to blue-green. Notably, in the solid state, the monomeric diradical species is predominantly formed under high hydrostatic pressure (>1 GPa).
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http://dx.doi.org/10.1002/chem.202005211DOI Listing
March 2021

Strong Impact of Intramolecular Hydrogen Bonding on the Cathodic Path of [Re(3,3'-dihydroxy-2,2'-bipyridine)(CO)Cl] and Catalytic Reduction of Carbon Dioxide.

Inorg Chem 2020 Apr 2;59(8):5564-5578. Epub 2020 Apr 2.

Department of Chemistry, University of Reading, Reading RG6 6AD, United Kingdom.

Herein, we present the cathodic paths of the Group-7 metal complex [Re(3,3'-DHBPY)(CO)Cl] (3,3'-DHBPY = 3,3'-dihydroxy-2,2'-bipyridine) producing a moderately active catalyst of electrochemical reduction of CO to CO. The combined techniques of cyclic voltammetry and IR/UV-vis spectroelectrochemistry have revealed significant differences in the chemistry of the electrochemically reduced parent complex compared to the previously published Re/4,4'-DHBPY congener. The initial irreversible cathodic step in weakly coordinating THF is shifted toward much less negative electrode potentials, reflecting facile reductive deprotonation of one hydroxyl group and strong intramolecular hydrogen bonding, O-H···O. The latter process occurs spontaneously in basic dimethylformamide where Re/4,4'-DHBPY remains stable. The subsequent reduction of singly deprotonated [Re(3,3'-DHBPY-H)(CO)Cl] under ambient conditions occurs at a cathodic potential close to that of the Re/4,4'-DHBPY-H derivative. However, for the stabilized 3,3'-DHBPY-H ligand, the latter process at the second cathodic wave is more complex and involves an overall transfer of three electrons. Rapid potential step electrolysis induces 1e-reductive cleavage of the second O-H bond, triggering dissociation of the Cl ligand from [Re(3,3'-DHBPY-2H)(CO)Cl]. The ultimate product of the second cathodic step in THF was identified as 5-coordinate [Re(3,3'-DHBPY-2H)(CO)], the equivalent of classical 2e-reduced [Re(BPY)(CO)]. Each reductive deprotonation of the DHBPY ligand results in a redshift of the IR ν(CO) absorption of the tricarbonyl complexes by ca. 10 cm, facilitating the product assignment based on comparison with the literature data for corresponding Re/BPY complexes. The Cl dissociation from [Re(3,3'-DHBPY-2H)(CO)Cl] was proven in strongly coordinating butyronitrile. The latter dianion is stable at 223 K, converting at 258 K to 6-coordinate [Re(3,3'-DHBPY-2H)(CO)(PrCN)]. Useful reference data were obtained with substituted parent [Re(3,3'-DHBPY)(CO)(PrCN)] that also smoothly deprotonates by the initial reduction to [Re(3,3'-DHBPY-H)(CO)(PrCN)]. The latter complex ultimately converts at the second cathodic wave to [Re(3,3'-DHBPY-2H)(CO)(PrCN)] via a counterintuitive ETC step generating the 1e radical of the parent complex, viz., [Re(3,3'-DHBPY)(CO)(PrCN)]. The same alternative reduction path is also followed by [Re(3,3'-DHBPY-H)(CO)Cl] at the onset of the second cathodic wave, where the ETC step results in the intermediate [Re(3,3'-DHBPY)(CO)Cl] further reducible to [Re(3,3'-DHBPY-2H)(CO)] as the CO catalyst.
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http://dx.doi.org/10.1021/acs.inorgchem.0c00263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7175459PMC
April 2020

Electronic Properties of Oxidized Cyclometalated Diiridium Complexes: Spin Delocalization Controlled by the Mutual Position of the Iridium Centers.

Chemistry 2020 Apr 12;26(20):4567-4575. Epub 2020 Mar 12.

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, 430079, P. R. China.

Four cyclometalated diiridium complexes, with IrCp*Cl (Cp*=η -C Me ) termini bridged by 1,4- and 1,3-bis(p-tolyliminoethyl)benzene (1, 2), or 1,4- and 1,3-bis(2-pyridyl)benzene (3, 4), were prepared and characterized by nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray diffraction (complexes 1, 2, and 4). The two iridium centers in complexes 1 and 3 are thus bound at the central benzene ring in the para-position (trans-Ir2), whereas those in complexes 2 and 4 are in the meta-position (cis-Ir2). Cyclic voltammograms of all four complexes show two consecutive one-electron oxidations. The potential difference between the two anodic steps in 1 and 3 is distinctly larger than that for 2 and 4. The visible-near-infrared (NIR)-short-wave infrared (SWIR) absorption spectra of trans-Ir2 monocations 1 and 3 are markedly different from those of cis-Ir2 monocations 2 and 4 . Notably, strong near-infrared electronic absorption appears only in the spectra of 1 and 3 whereas 2 and 4 absorb only weakly in the NIR-SWIR region. Combined DFT and TD-DFT calculations have revealed that (a) 1 and 3 (the diiridium-benzene trans-isomers) display the highest occupied spin-orbitals (HOSO) and the lowest unoccupied spin-orbital (LUSO) evenly delocalized over both molecule halves, and (b) their electronic absorptions in the NIR-SWIR region are attributed to mixed metal-to-ligand and ligand-to-ligand charge transfers (MLCT and LLCT). In contrast, cis-isomers 2 and 4 do not feature this stabilizing π-delocalization but a localized mixed-valence state showing a weak intervalence charge-transfer (IVCT) absorption in the SWIR region.
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http://dx.doi.org/10.1002/chem.201904894DOI Listing
April 2020

Spectro-electrochemical Studies on [Ru(TAP)(dppz)]-Insights into the Mechanism of its Photosensitized Oxidation of Oligonucleotides.

Inorg Chem 2019 Jan 12;58(1):663-671. Epub 2018 Dec 12.

School of Chemical Sciences , Dublin City University , Dublin 9 , Ireland.

[Ru(TAP)(dppz)] (TAP = 1,4,5,8-tetraazaphenanthrene; dppz = dipyrido[3,2- a:2',3'- c]phenazine) is known to photo-oxidize guanine in DNA. Whether this oxidation proceeds by direct photoelectron transfer or by proton-coupled electron transfer is still unknown. To help distinguish between these mechanisms, spectro-electrochemical experiments have been carried out with [Ru(TAP)(dppz)] in acetonitrile. The UV-vis and mid-IR spectra obtained for the one-electron reduced product were compared to those obtained by picosecond transient absorption and time-resolved infrared experiments of [Ru(TAP)(dppz)] bound to guanine-containing DNA. An interesting feature of the singly reduced species is an electronic transition in the near-IR region (with λ at 1970 and 2820 nm). Density functional and time-dependent density functional theory simulations of the vibrational and electronic spectra of [Ru(TAP)(dppz)], the reduced complex [Ru(TAP)(dppz)], and four isomers of [Ru(TAP)(TAPH)(dppz)] (a possible product of proton-coupled electron transfer) were performed. Significantly, these predict absorption bands at λ > 1900 nm (attributed to a ligand-to-metal charge-transfer transition) for [Ru(TAP)(dppz)] but not for [Ru(TAP)(TAPH)(dppz)]. Both the UV-vis and mid-IR difference absorption spectra of the electrochemically generated singly reduced species [Ru(TAP)(dppz)] agree well with the transient absorption and time-resolved infrared spectra previously determined for the transient species formed by photoexcitation of [Ru(TAP)(dppz)] intercalated in guanine-containing DNA. This suggests that the photochemical process in DNA proceeds by photoelectron transfer and not by a proton-coupled electron transfer process involving formation of [Ru(TAP)(TAPH)(dppz)], as is proposed for the reaction with 5'-guanosine monophosphate. Additional infrared spectro-electrochemical measurements and density functional calculations have also been carried out on the free TAP ligand. These show that the TAP radical anion in acetonitrile also exhibits strong broad near-IR electronic absorption (λ at 1750 and 2360 nm).
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http://dx.doi.org/10.1021/acs.inorgchem.8b02859DOI Listing
January 2019

Diphenylamine-Substituted Osmanaphthalyne Complexes: Structural, Bonding, and Redox Properties of Unusual Donor-Bridge-Acceptor Systems.

Chemistry 2018 Dec 20;24(71):18998-19009. Epub 2018 Nov 20.

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, 430079, P. R. China.

Diarylamine-substituted osmanaphthalyne complexes that feature two redox centers linked by the rigid skeleton of the metallacycle (C^C ), specifically, [OsCl (PPh ) {(C^C )NAr }][BF ] (Ar=Ph (1 a), p-MeOPh (1 b)) and their open-ring precursors [OsHCl (PPh ) {(≡C-C(PPh )=CHPh)NR }][BF ] (Ar=Ph (2 a), p-MeOPh (2 b)), were successfully synthesized and characterized by H, C, and P NMR spectroscopy, ESI-MS, and elemental analysis. The solid-state molecular structures of complexes 1 a and 2 a were ascertained by single-crystal X-ray diffraction. The Os≡C bond length in both complexes 1 a and 2 a fell within the range reported for similar osmanaphthalynes and osmium carbyne complexes, respectively. The structural parameters determined for complex 1 a, which were successfully reproduced by theoretical calculations, point to a π-delocalized metallacycle structure. The purple color of compounds 1 a and b was explained by the diarylamine→Os(metallacycle) charge-transfer absorption in the visible region. The neutral, one-electron-oxidized and one-electron-reduced states of compounds 1 a, b, and a reference complex that lacked the diarylamine substituent, [OsCl (PPh ) {(C^C )}][BF ] (1'), were investigated by cyclic and square-wave voltammetry, UV/Vis/NIR spectroelectrochemistry, and DFT calculations. The spin density in singly oxidized complexes [1 a] and [1 b] predominantly resided on the aminyl segment, with osmium involvement controlled by the diphenylamine substitution. Spin density in stable, singly-reduced [1'] was distributed mainly over the osmanaphthalyne metallacycle.
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http://dx.doi.org/10.1002/chem.201804025DOI Listing
December 2018

Accurate Description of Low-Lying Excited States in a Series of Photoreactive Clusters [Os(CO)(α-diimine)] by DFT Calculations.

Inorg Chem 2018 Sep 6;57(18):11704-11716. Epub 2018 Sep 6.

Centro de Química e Bioquímica and BioISI - Biosystems & Integrative Sciences Institute, Departamento de Química e Bioquímica, Faculdade de Ciências , Universidade de Lisboa , 1749-016 Lisboa , Portugal.

Density functional theory (DFT) calculations were performed on clusters [Os(CO)(α-diimine)], for α-diimine = 2,2'-bipyridine (BPY), N-isopropyl 2-iminomethylpyridine (IMP), and N, N'-diisopropyl-l,4-diaza-1,3-butadiene (DAB), together with their spectroscopic study. This important family of clusters is known to convert upon irradiation with visible light into short-lived biradicals and long-lived zwitterions from a σπ* (SBLCT) excited state that has not been described accurately thus far by quantum mechanical calculations. On the basis of the combined DFT, UV-vis absorption, and resonance Raman data, the lowest-lying visible absorption band is assigned to a σ(Os1-Os3)-to-π*(α-diimine) CT transition, for α-diimine = bpy and IMP, and to a strongly delocalized σ(Os1-Os3)π*-to-σ*(Os1-Os3)π* transition for conjugated nonaromatic α-diimine = DAB. The DFT calculations rationalize the experimentally determined characteristics of this electronic transition in the studied series: (i) The corresponding absorption band is the dominant feature in the visible spectral region. (ii) The CT character of the electronic excitation declines from α-diimine = bpy to IMP and vanishes for DAB. (iii) The excitation energies decrease in the order α-diimine = DAB > BPY > IMP. (iv) The oscillator strength shrinks in the order α-diimine = DAB > IMP > BPY. Reference photoreaction quantum yields measured accurately for the formation of a cluster zwitterion from [Os(CO)(IMP)] in strongly coordinating pyridine demonstrate that the optical population of the lowest-energy σπ* and relaxed σπ* excited states in the DFT model scheme is still capable of inducing the initial homolytic Os1-Os3 σ-bond splitting, although less efficiently than the optical excitation into neighbor higher-lying electronic transitions due to a higher potential barrier for the reaction from a dissociative (σσ*) state.
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http://dx.doi.org/10.1021/acs.inorgchem.8b01847DOI Listing
September 2018

Synthesis, electronic structure and redox properties of the diruthenium sandwich complexes [Cp*Ru(μ-CH)RuCp*] (x = 0, 1+; Cp* = CMe; CH = naphthalene).

Dalton Trans 2018 Aug;47(32):11058-11069

University of Regensburg, Institute of Inorganic Chemistry, 93040 Regensburg, Germany.

The dinuclear ruthenium complex [Cp*Ru(μ-C10H8)RuCp*] (1; Cp* = η5-C5Me5) was prepared by reduction of the cationic precursor [Cp*Ru(η6-C10H8)]PF6 with KC8. Diamagnetic 1 has a symmetric molecular structure with an anti-facial configuration of the Cp*Ru moieties coordinating to naphthalene. Density Functional Theory (DFT) studies showed an electronic structure similar to that of the analogous diiron complex [Cp*Fe(μ-C10H8)FeCp*]. Cyclic voltammetry and UV-vis spectroelectrochemistry showed that 1 can be reversibly oxidized to 1+ and 12+. Chemical oxidation with [Cp2Fe]BArF4 afforded the paramagnetic compound [1]BArF4, which was investigated by EPR, single-crystal X-ray diffractometry and DFT calculations. Reaction of 1 with Brookhart's acid gave the hydride complex [3]BArF4, which was characterized spectroscopically and crystallographically. Cyclic voltammetry showed that [3]+ is converted back to 1 upon reduction and oxidation.
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http://dx.doi.org/10.1039/c8dt02003eDOI Listing
August 2018

Excited-State Electronic Asymmetry Prevents Photoswitching in Terthiophene Compounds.

Inorg Chem 2018 Aug 20;57(15):9039-9047. Epub 2018 Jul 20.

Department of Chemistry , University of Reading , Whiteknights, Reading RG6 6AD , United Kingdom.

The diarylethene moiety is one of the most extensively used switches in the field of molecular electronics. Here we report on spectroscopic and quantum chemical studies of two diarylethene-based compounds with a non- C-symmetric triethynyl terthiophene core symmetrically substituted with RuCp*(dppe) or trimethylsilyl termini. The ethynyl linkers are strong IR markers that we use in time-resolved vibrational spectroscopic studies to get insight into the character and dynamics of the electronically excited states of these compounds on the picosecond to nanosecond time scale. In combination with electronic transient absorption studies and DFT calculations, our studies show that the conjugation of the non- C-symmetric triethynyl terthiophene system in the excited state strongly affects one of the thiophene rings involved in the ring closure. As a result, cyclization of the otherwise photochromic 3,3″-dimethyl-2,2':3',2″-terthiophene core is inhibited. Instead, the photoexcited compounds undergo intersystem crossing to a long-lived triplet excited state from which they convert back to the ground state.
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http://dx.doi.org/10.1021/acs.inorgchem.8b01005DOI Listing
August 2018

A macrocyclic receptor containing two viologen species connected by conjugated terphenyl groups.

Org Biomol Chem 2018 07;16(27):5006-5015

Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6AD, UK.

A macrocyclic receptor molecule containing two viologen species connected by conjugated terphenyl groups has been designed and synthesised. The single-crystal X-ray structure shows that the two viologen residues have a transannular NN separation of ca. 7.4 Å. Thus, the internal cavity dimensions are suitable for the inclusion of π-electron-rich species. The macrocycle is redox active, and can accept electrons from suitable donor species including triethylamine, resulting in a dramatic colour change from pale yellow to dark green as a consequence of the formation of a paramagnetic bis(radical cationic) species. Cyclic voltammetry shows that the macrocycle can undergo two sequential and reversible reduction processes (E1/2 = -0.65 and -0.97 V vs. Fc/Fc+). DFT and TD-DFT studies accurately replicate the structure of the tetracationic macrocycle and the electronic absorption spectra of the three major redox states of the system. These calculations also showed that during electrochemical reduction, the unpaired electron density of the radical cations remained relatively localised within the heterocyclic rings. The ability of the macrocycle to form supramolecular complexes was confirmed by the formation of a pseudorotaxane with a guest molecule containing a π-electron-rich 1,5-dihydroxynaphthalene derivative. Threading and dethreading of the pseudorotaxane was fast on the NMR timescale, and the complex exhibited an association constant of 150 M-1 (±30 M-1) as calculated from 1H NMR titration studies.
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http://dx.doi.org/10.1039/c8ob00919hDOI Listing
July 2018

Anodic electrochemistry of mono- and dinuclear aminophenylferrocene and diphenylaminoferrocene complexes.

Dalton Trans 2018 May;47(17):6112-6123

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P.R. China.

Two related three-membered series of nonlinear aminophenylferrocene and diphenylaminoferrocene complexes were prepared and characterized by 1H and 13C NMR spectroscopy. The first series consists of 4-(diphenylamino)phenylferrocene (TPA-Fc, 1a), its dimethoxy-substituted tetraphenylphenylenediamine derivative (M2TPPD-Fc, 1c), and the triphenylamine-bridged bis(ferrocenyl) complex (Fc-TPA-Fc, 1b). The second series involves bis(4-methoxyphenyl)aminoferrocene (M2DPA-Fc, 1d), 4-methoxyphenylaminoferrocene (MPA-Fc) with N-phenyl-appended terminal TPA (1e), and the corresponding bis(MPA-Fc) complex with bridging TPA (1f). The structure of complex 1d was further confirmed by single crystal X-ray diffraction. Combined investigations, based on anodic voltammetry, UV-vis-NIR spectroelectrochemistry and density functional theory (DFT) calculations, were conducted to illustrate the influence of the integration of multiple redox-active components on the sequential oxidation of these complexes. The first anodic steps in 1a-1f are localized preferentially on the ferrocenyl units, followed by oxidation of the TPA or TPPD moieties (absent in 1d). Irreversible oxidation of the ferrocene-appended strong donor DPA/MPA units in 1d-1f terminates the anodic series. The one-electron oxidation of the triphenylamine-bridged diferrocenyl (1b) and bis(phenylaminoferrocenyl) (1f) complexes triggers their facile redox disproportionation to dicationic bis(ferrocenium) products.
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http://dx.doi.org/10.1039/c8dt00584bDOI Listing
May 2018

Structural Variability of 4f and 5f Thiocyanate Complexes and Dissociation of Uranium(III)-Thiocyanate Bonds with Increased Ionicity.

Inorg Chem 2017 Dec 16;56(23):14426-14437. Epub 2017 Nov 16.

School of Chemistry, University of Dublin, Trinity College , Dublin 2, Ireland.

A series of complexes [EtN][Ln(NCS)(HO)] (Ln = Pr, Tb, Dy, Ho, Yb) have been structurally characterized, all showing the same structure, namely a distorted square antiprismatic coordination geometry, and the Ln-O and Ln-N bond lengths following the expected lanthanide contraction. When the counterion is Cs, a different structural motif is observed and the eight-coordinate complex Cs[Nd(NCS)] isolated. The thorium compounds [MeN][Th(NCS)(NO)] and [MeN][Th(NCS)(NO)] have been characterized, and high coordination numbers are also observed. Finally, attempts to synthesize a U(III) thiocyanate compound has been unsuccessful; from the reaction mixture, a heterocycle formed by condensation of five MeCN solvent molecules, possibly promoted by U(III), was isolated and structurally characterized. To rationalize the inability to isolate U(III) thiocyanate compounds, thin-layer cyclic voltammetry and IR spectroelectrochemistry have been utilized to explore the cathodic behavior of [EtN][U(NCS)] and [EtN][U(NCS)(bipy)] along with a related uranyl compound [EtN][UO(NCS)]. In all examples, the reduction triggers a rapid dissociation of [NCS] ions and decomposition. Interestingly, the oxidation chemistry of [EtN][UO(NCS)] in the presence of bipy gives the U(IV) compound [EtN][U(NCS)], an unusual example of a ligand-based oxidation triggering a metal-based reduction. The experimental results have been augmented by a computational investigation, concluding that the U(III)-NCS bond is more ionic than the U(IV)-NCS bond.
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http://dx.doi.org/10.1021/acs.inorgchem.7b01560DOI Listing
December 2017

Bonding and Electronic Properties of Linear Diethynyl Oligothienoacene-Bridged Diruthenium Complexes and Their Oxidized Forms.

Inorg Chem 2017 Sep 29;56(18):11074-11086. Epub 2017 Aug 29.

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University (CCNU) , Wuhan 430079, P. R. China.

A series of five diruthenium diethynyl complexes based on α,β-fused oligothienoacenes in the core of the bridging ligands [{Ru(dppe)Cp*}(μ-C≡C-L-C≡C)] [dppe = 1,2-bis(diphenylphosphino)ethane, Cp* = η-CMe; L = thieno[3,2-b]thiophene (4), thieno[2,3-b]thiophene (5), 3,4-dimethylthieno[2,3-b]thiophene (6), dithieno[3,2-b:2',3'-d]thiophene (7), and thieno[3,2-b]thieno[2',3':4,5]thieno[2,3-d]thiophene (8)] have been synthesized and fully characterized electrochemically and spectroscopically. Elongation of the redox noninnocent oligothienoacene bridge core causes a smaller potential difference between the initial two anodic steps, not seen for free dialkyl oligothienoacenes, and increased positive charge delocalization over the conjugated bridge backbone. The highest occupied molecular orbital of the parent complexes resides predominantly on the oligothienoacene core, with strong participation of the ethynyl linkers and slightly smaller contribution from the metallic termini. This bonding character makes the initial one-electron oxidation symmetrical, as revealed by combined voltammetric and spectroscopic (IR, UV-vis-near-IR, and electron paramagnetic resonance) methods as well as density functional theory (DFT) and time-dependent DFT calculations of truncated and selected nontruncated models of the studied series. The remarkable gradual appearance of two C≡C stretching absorptions in the IR spectra of the monocationic diethynyl complexes is ascribed to increasing vibronic coupling of the IR-forbidden ν(C≡C) mode of the oxidized -[C≡C-core-C≡C]- bridge with a low-lying π-π*(intrabridge)/metal-to-ligand charge-transfer electronic transition in the near-to-mid-IR spectral region.
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http://dx.doi.org/10.1021/acs.inorgchem.7b01433DOI Listing
September 2017

New Multiresponsive Chromic Soft Materials: Dynamic Interconversion of Short 2,7-Dicyanomethylenecarbazole-Based Biradicaloid and the Corresponding Cyclophane Tetramer.

Chemistry 2017 Oct 5;23(55):13776-13783. Epub 2017 Sep 5.

Key Laboratory of Synthetic and Self-assembly Chemistry for Organic Functional Materials, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, No. 345 Lingling Rd., Shanghai, 200032, P. R. China.

This work reports on a quinodimethane-type molecule, 2,7-dicyanomethylene-9-(2-ethylhexyl)carbazole (1), one of the shortest π-conjugated biradicaloids reported to be stable in solution under ambient conditions. This carbazole-based quinoidal precursor is able to form a macrocyclic σ-bonded tetramer (2). The resolved single-crystal X-ray structure of tetramer 2 shows that four molecules of 1 are linked together through four long (CN) C-C(CN) bonds (1.631 Å) resulting from coupling of the unpaired electrons in biradicaloid 1. Dynamic interconversion between monomer 1 and cyclophane tetramer 2 is achieved by reversible cleavage and recovery of the four (CN) C-C(CN) bonds upon soft external stimuli (light absorption, temperature and pressure), which is accompanied by significant color changes. These novel photo-, thermo-, and mechanochromic properties expand the versatility of π-conjugated biradicaloid compounds as novel functional materials that, in combination with spin chemistry and dynamic covalent chemistry, can be relevant in molecular machines, sensors, and switches.
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http://dx.doi.org/10.1002/chem.201702659DOI Listing
October 2017

Sandwich and half-sandwich metal complexes derived from cross-conjugated 3-methylene-penta-1,4-diynes.

Dalton Trans 2017 May;46(17):5522-5531

Department of Chemistry, Durham University, South Rd, Durham, DH1 3LE, UK and School of Chemistry and Biochemistry, University of Western Australia, 35 Stirling Highway, Crawley 6009, WA, Australia.

The cross-conjugated ethynyl-vinylidene [PhC[double bond, length as m-dash]C(C[triple bond, length as m-dash]CH){C(H)[double bond, length as m-dash]CRu(PPh)Cp}]PF ([4a]PF), and [FcC(H)[double bond, length as m-dash]C(C[triple bond, length as m-dash]CH){C(H)[double bond, length as m-dash]CRu(PPh)Cp}]PF ([4b]PF), and ethynyl-alkynyl PhC[double bond, length as m-dash]C(C[triple bond, length as m-dash]CH){C[triple bond, length as m-dash]CRu(PPh)Cp} (5a), and FcC(H)[double bond, length as m-dash]C(C[triple bond, length as m-dash]CH){C[triple bond, length as m-dash]CRu(PPh)Cp} (5b) compounds (Cp = η-cyclopentadienyl) have been prepared from reactions of the known 3-methylene-penta-1,4-diynes PhC[double bond, length as m-dash]C(C[triple bond, length as m-dash]CH) (3a) and [FcCH[double bond, length as m-dash]C(C[triple bond, length as m-dash]CH)] (3b) with [RuCl(PPh)Cp]. The compounds derived from 3b incorporating the more electron-rich alkene proved to be unstable during work-up, and attempts to prepare bis(ruthenium) complexes from 3a and 3b or from transmetallation reactions of the bis(alkynylgold) complex FcCH[double bond, length as m-dash]C(C[triple bond, length as m-dash]CAuPPh) (7) with RuCl(PPh)Cp were unsuccessful. The related bis- and tris(ferrocenyl) derivatives PhC[double bond, length as m-dash]C(C[triple bond, length as m-dash]CFc) (6a) and FcCH[double bond, length as m-dash]C(C[triple bond, length as m-dash]CFc) (6b) were more readily obtained from Pd(ii)/Cu(i) catalysed cross-coupling reactions of FcC[triple bond, length as m-dash]CH with the 1,1-dibromo vinyl complexes PhC[double bond, length as m-dash]CBr (1a) and FcC(H)[double bond, length as m-dash]CBr (1b). Cyclic voltammetry of 6a and 6b using n-BuN[PF] as the supporting electrolyte shows broad, overlapping waves arising from the sequential oxidation of the ferrocenyl moieties in electronically and chemically similar environments. Electrostatic effects between the ferrocenyl moieties are enhanced in solutions of the weakly ion-pairing electrolyte n-BuN[B{CH(CF)-3,5}], leading to better resolution of the individual electrochemical processes. The comparative IR spectroelectrochemical response of 6a and 6b suggest the vinyl ferrocene moiety in 6b undergoes oxidation before the ethynyl ferrocene fragments. There is no evidence of electronic coupling between the metallocene moieties and [6a], [6b] (n = 1, 2) are best described as Class I mixed-valence compounds.
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http://dx.doi.org/10.1039/c6dt04470kDOI Listing
May 2017

Multistep Oxidation of Diethynyl Oligophenylamine-Bridged Diruthenium and Diiron Complexes.

Inorg Chem 2017 Jan 3;56(2):1001-1015. Epub 2017 Jan 3.

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University , Wuhan 430079, P. R. China.

Homo-dinuclear nonlinear complexes [{M(dppe)Cp*}{μ-(-C≡C)X}] (dppe = 1,2-bis(diphenylphosphino)ethane; Cp* = η-CMe; X = triphenylamine (TPA), M = Ru (1a) and Fe (1b); X = N,N,N',N'-tetraphenylphenylene-1,4-diamine (TPPD), M = Ru (2a)) were prepared and characterized by H, C, and P NMR spectroscopy and single-crystal X-ray diffraction (1a, 2a). Attempts to prepare the diiron analogue of 2a were not successful. Experimental data obtained from cyclic voltammetry, square wave voltammetry, UV-vis-NIR (NIR = near-infrared) spectro-electrochemistry, and very informative IR spectro-electrochemistry in the C≡C stretching region, combined with density functional theory calculations, afford to make an emphasizing assessment of the close association between the metal-ethynyl termini and the oligophenylamine bridge core as well as their respective involvement in sequential one-electron oxidations of these complexes. The anodic behavior of the homo-bimetallic complexes depends strongly both on the metal center and the length of the oligophenylamine bridge core. The poorly separated first two oxidations of diiron complex 1b are localized on the electronically nearly independent Fe termini. In contrast, diruthenium complex 1a exhibits a significantly delocalized character and a marked electronic communication between the ruthenium centers through the diethynyl-TPA bridge. The ruthenium-ethynyl halves in 2a, separated by the doubly extended and more flexible TPPD bridge core, show a lower degree of electronic coupling, resulting in close-lying first two anodic waves and the NIR electronic absorption of [2a] with an indistinctive intervalence charge transfer character. Finally, the third anodic waves in the voltammetric responses of the homo-bimetallic complexes are associated with the concurrent exclusive oxidation of the TPA or TPPD bridge cores.
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http://dx.doi.org/10.1021/acs.inorgchem.6b02809DOI Listing
January 2017

Diacenaphthylene-fused benzo[1,2-b:4,5-b']dithiophenes: polycyclic heteroacenes containing full-carbon five-membered aromatic rings.

Chem Commun (Camb) 2017 Jan;53(4):751-754

Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 200032, China.

We herein report on an efficient synthesis of diacenaphthylene-fused benzo[1,2-b:4,5-b']dithiophenes and demonstrate that their packing structure in the solid state depends on the substituent groups. These compounds form dimers with their radical cations in high concentration solution and exhibit good field-effect mobility.
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http://dx.doi.org/10.1039/c6cc09184aDOI Listing
January 2017

Manganese Tricarbonyl Complexes with Asymmetric 2-Iminopyridine Ligands: Toward Decoupling Steric and Electronic Factors in Electrocatalytic CO Reduction.

Inorg Chem 2016 Dec 23;55(24):12568-12582. Epub 2016 Nov 23.

Department of Chemistry, University of Sheffield , Sheffield S3 7HF, U.K.

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)pyridine) derivatives, [MnBr(CO)(IP)], are demonstrated as a new group of catalysts for CO reduction, which represent the first example of utilization of (phenylimino)pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV-vis-IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical-chemical-electrochemical) formation of a five-coordinate anion [Mn(CO)(IP)], a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)imino)methyl]pyridine), TBIMP (2-[((2-tert-butylphenyl)imino)methyl]pyridine), and TBIEP (2-[((2-tert-butylphenyl)imino)ethyl]pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr(CO)(IMP)] (2-[(phenylimino)methyl]pyridine) by the stepwise formation of such a monoanion via an ECEC(E) mechanism involving also the intermediate Mn-Mn dimer [Mn(CO)(IMP)]. The complex [MnBr(CO)(IPIMP)] (2-[((2-diisopropylphenyl)imino)methyl]pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. -2.2 V vs Fc/Fc), recovering [Mn(CO)(IP)] and triggering the catalytic production of CO.
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http://dx.doi.org/10.1021/acs.inorgchem.6b01477DOI Listing
December 2016

Localized Mixed-Valence and Redox Activity within a Triazole-Bridged Dinucleating Ligand upon Coordination to Palladium.

Chemistry 2016 Sep 17;22(39):13965-13975. Epub 2016 Aug 17.

Homogeneous, Bioinspired and Supramolecular Catalysis, van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands.

The new dinucleating redox-active ligand (L ), bearing two redox-active NNO-binding pockets linked by a 1,2,3-triazole unit, is synthetically readily accessible. Coordination to two equivalents of Pd resulted in the formation of paramagnetic (S=1/2 ) dinuclear Pd complexes with a κ -N,N'-bridging triazole and a single bridging chlorido or azido ligand. A combined spectroscopic, spectroelectrochemical, and computational study confirmed Robin-Day Class II mixed-valence within the redox-active ligand, with little influence of the secondary bridging anionic ligand. Intervalence charge transfer was observed between the two ligand binding pockets. Selective one-electron oxidation allowed for isolation of the corresponding cationic ligand-based diradical species. SQUID (super-conducting quantum interference device) measurements of these compounds revealed weak anti-ferromagnetic spin coupling between the two ligand-centered radicals and an overall singlet ground state in the solid state, which is supported by DFT calculations. The rigid and conjugated dinucleating redox-active ligand framework thus allows for efficient electronic communication between the two binding pockets.
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http://dx.doi.org/10.1002/chem.201601900DOI Listing
September 2016

Notable differences between oxidized diruthenium complexes bridged by four isomeric diethynyl benzodithiophene ligands.

Dalton Trans 2016 Apr;45(15):6503-16

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P. R. China.

Four new diruthenium complexes [{(η(5)-C5Me5)Ru(dppe)}2(μ-C[triple bond, length as m-dash]C-L-C[triple bond, length as m-dash]C)] featuring different bridging isomeric diethynyl benzodithiophenes viz. L = benzo[1,2-b;4,5-b']dithiophene (complex ), benzo[2,1-b;4,5-b']dithiophene (complex ), benzo[1,2-b;3,4-b']dithiophene (complex ) and benzo[1,2-b;4,3-b']dithiophene (complex ), were synthesized and characterized by molecular spectroscopic and crystallographic methods. The subtle changes in the molecular structure introduced by the diethynyl benzodithiophene isomers have a notable impact on the stability of the oxidized complexes and their absorption characteristics in the visible-NIR and IR spectral domains. Electronic properties of stable oxidized complexes [](n+) and [](n+) (n = 1, 2) were investigated by cyclic voltammetry, UV-vis-NIR and IR spectroelectrochemistry as well as DFT and TDDFT calculations. The results document the largely bridge-localized character of the oxidation of parents and . Cations [](+) and [](+) are too unstable at ambient temperature to afford their unambiguous characterization. UV-vis-NIR absorption spectral data combined with TDDFT calculations (BLYP35) reveal that the broad electronic absorption of [](+) and [](+) in the NIR region has a mixed intraligand π-π* and MLCT character, with similar contribution from their spin-delocalized trans and cis conformers. A spin-localized (mixed-valence) rotamer was only observed for [](+) at ambient temperature as a minor component on the time scale of IR spectroscopy.
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http://dx.doi.org/10.1039/c6dt00109bDOI Listing
April 2016

Effects of Electrode-Molecule Binding and Junction Geometry on the Single-Molecule Conductance of bis-2,2':6',2″-Terpyridine-based Complexes.

Inorg Chem 2016 Mar 24;55(6):2691-700. Epub 2016 Feb 24.

School of Chemistry and Biochemistry, University of Western Australia , 35 Stirling Highway, Crawley, Perth, Washington 6009, Australia.

The single molecule conductances of a series of bis-2,2':6',2″-terpyridine complexes featuring Ru(II), Fe(II), and Co(II) metal ions and trimethylsilylethynyl (Me3SiC≡C-) or thiomethyl (MeS-) surface contact groups have been determined. In the absence of electrochemical gating, these complexes behave as tunneling barriers, with conductance properties determined more by the strength of the electrode-molecule contact and the structure of the "linker" than the nature of the metal-ion or redox properties of the complex.
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http://dx.doi.org/10.1021/acs.inorgchem.5b02094DOI Listing
March 2016

Asymmetric oxidation of vinyl- and ethynyl terthiophene ligands in triruthenium complexes.

Dalton Trans 2016 Jan;45(2):768-82

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P.R. China.

A series of ruthenium(ii) complexes [{RuCl(CO)(PMe3)3(-CH[double bond, length as m-dash]CH-)}nX], (: n = 3, X = 3,3''-dimethyl-2,2':3',2''-terthiophene; : n = 2, X = 2,2'-bithiophene; : n = 2, X = 2,3-bis(3-methylthiophen-2-yl)benzothiophene) and [{Cp*(dppe)2Ru(-C[triple bond, length as m-dash]C-)}3X], (X = 3,3''-dimethyl-2,2':3',2''-terthiophene), were prepared and characterized by (1)H, (13)C and (31)P NMR. Their redox, spectroscopic and bonding properties were studied with a range of spectro-electrochemical methods in combination with density functional theory calculations. The first two anodic steps observed for and are largely localized on the lateral frameworks of the molecular triangle, the direct conjugation between them being precluded due to the photostable open form of the dithienyl ethene moiety. The third anodic step is then mainly localized on the centerpiece of the triangular structure, affecting both bithiophene laterals. The experimental IR and UV-vis-NIR spectroelectrochemical data and, largely, also DFT calculations account for this explanation, being further supported by direct comparison with the anodic behavior of reference diruthenium complexes and .
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http://dx.doi.org/10.1039/c5dt04083cDOI Listing
January 2016

Efficient access to conjugated 4,4'-bipyridinium oligomers using the Zincke reaction: synthesis, spectroscopic and electrochemical properties.

Org Biomol Chem 2016 Jan 2;14(3):980-8. Epub 2015 Dec 2.

Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6AD, UK.

The cyclocondensation reaction between rigid, electron-rich aromatic diamines and 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridinium (Zincke) salts has been harnessed to produce a series of conjugated oligomers containing up to twelve aromatic/heterocyclic residues. These oligomers exhibit discrete, multiple redox processes accompanied by dramatic changes in electronic absorption spectra.
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http://dx.doi.org/10.1039/c5ob02211hDOI Listing
January 2016

Electrochemical Single-Molecule Transistors with Optimized Gate Coupling.

J Am Chem Soc 2015 Nov 4;137(45):14319-28. Epub 2015 Nov 4.

Department of Chemistry, University of Reading , Whiteknights, Reading, RG6 6AD, U.K.

Electrochemical gating at the single molecule level of viologen molecular bridges in ionic liquids is examined. Contrary to previous data recorded in aqueous electrolytes, a clear and sharp peak in the single molecule conductance versus electrochemical potential data is obtained in ionic liquids. These data are rationalized in terms of a two-step electrochemical model for charge transport across the redox bridge. In this model the gate coupling in the ionic liquid is found to be fully effective with a modeled gate coupling parameter, ξ, of unity. This compares to a much lower gate coupling parameter of 0.2 for the equivalent aqueous gating system. This study shows that ionic liquids are far more effective media for gating the conductance of single molecules than either solid-state three-terminal platforms created using nanolithography, or aqueous media.
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http://dx.doi.org/10.1021/jacs.5b08431DOI Listing
November 2015

Elucidating the Structure of Chiral Molecules by using Amplified Vibrational Circular Dichroism: From Theory to Experimental Realization.

Chemphyschem 2015 Nov 9;16(16):3363-73. Epub 2015 Sep 9.

Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands.

Recent experimental observations of enhanced vibrational circular dichroism (VCD) in molecular systems with low-lying electronically excited states suggest interesting new applications of VCD spectroscopy. The theory describing VCD enhancement through vibronic coupling schemes was derived by Nafie in 1983, but only recently experimental evidence of VCD amplification has demonstrated the extent to which this effect can be exploited as a structure elucidation tool to probe local structure. In this Concept paper, we give an overview of the physics behind vibrational circular dichroism, in particular the equations governing the VCD amplification effect, and review the latest experimental developments with a prospective view on the application of amplified VCD to locally probe biomolecular structure.
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http://dx.doi.org/10.1002/cphc.201500551DOI Listing
November 2015

Switchable amplification of vibrational circular dichroism as a probe of local chiral structure.

Angew Chem Int Ed Engl 2014 Dec 11;53(51):14042-5. Epub 2014 Sep 11.

Molecular Photonics Group, Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands).

A new method to detect the vibrational circular dichroism (VCD) of a localized part of a chiral molecular system is reported. A local VCD amplifier was implemented, and the distance dependence of the amplification was investigated in a series of peptides. The results indicate a characteristic distance of 2.0±0.3 bonds, which suggests that the amplification is a localized phenomenon. The amplifier can be covalently coupled to a specific part of a molecule, and can be switched ON and OFF electrochemically. By subtracting the VCD spectra obtained when the amplifier is in the ON and OFF states, the VCD of the local environment of the amplifier can be separated from the total VCD spectrum. Switchable local VCD amplification thus makes it possible to "zoom in" on a specific part of a chiral molecule.
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http://dx.doi.org/10.1002/anie.201407376DOI Listing
December 2014

Thiocyanate complexes of uranium in multiple oxidation states: a combined structural, magnetic, spectroscopic, spectroelectrochemical, and theoretical study.

Inorg Chem 2014 Aug 29;53(16):8624-37. Epub 2014 Jul 29.

School of Chemistry, University of Dublin, Trinity College , College Green, Dublin 2, Ireland.

A comprehensive study of the complexes A4[U(NCS)8] (A = Cs, Et4N, (n)Bu4N) and A3[UO2(NCS)5] (A = Cs, Et4N) is described, with the crystal structures of [(n)Bu4N]4[U(NCS)8]·2MeCN and Cs3[UO2(NCS)5]·O0.5 reported. The magnetic properties of square antiprismatic Cs4[U(NCS)8] and cubic [Et4N]4[U(NCS)8] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, μeff = 1.21 μB and 0.53 μB, respectively. Electronic absorption and photoluminescence spectra of the uranium(IV) compounds have been measured. The redox chemistry of [Et4N]4[U(NCS)8] has been explored using IR and UV-vis spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc(+), followed by an irreversible oxidation to form dithiocyanogen (NCS)2 which upon back reduction regenerates thiocyanate anions coordinating to UO2(2+). NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U(NCS)8](4-) is delocalized over all NCS(-) ligands. Reduction of the uranyl(VI) complex [Et4N]3[UO2(NCS)5] to uranyl(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An(NCS)8](4-) (An = Th, U) and [UO2(NCS)5](3-) has been explored by a combination of DFT and QTAIM analysis, and the U-N bonds are predominantly ionic, with the uranyl(V) species more ionic that the uranyl(VI) ion. Additionally, the U(IV)-NCS ion is more ionic than what was found for U(IV)-Cl complexes.
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http://dx.doi.org/10.1021/ic501236jDOI Listing
August 2014

Multistep π dimerization of tetrakis(n-decyl)heptathienoacene radical cations: a combined experimental and theoretical study.

Chemistry 2014 Aug 17;20(33):10351-9. Epub 2014 Jul 17.

Department of Physical Chemistry, University of Málaga, Campus de Teatinos s/n, Málaga 29071 (Spain), Fax: (+34) 952132000.

Radical cations of a heptathienoacene α,β-substituted with four n-decyl side groups (D4T7(.) (+) ) form exceptionally stable π-dimer dications already at ambient temperature (Chem. Comm. 2011, 47, 12622). This extraordinary π-dimerization process is investigated here with a focus on the ultimate [D4T7(.) (+) ]2 π-dimer dication and yet-unreported transitory species formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the π-dimerization process is also investigated in detail. Two different transitory species were detected in the course of the one-electron oxidation: 1) a different transient conformation of the ultimate [D4T7(.) (+) ]2 π-dimer dications, the stability of which is strongly affected by the applied experimental conditions, and 2) intermediate [D4T7]2 (.) (+) π-dimer radical cations formed prior to the fully oxidized [D4T7]2 (.) (+) π-dimer dications. Thus, this comprehensive work demonstrates the formation of peculiar supramolecular species of heptathienoacene radical cations, the stability, nature, and structure of which have been successfully analyzed. We therefore believe that this study leads to a deeper fundamental understanding of the mechanism of dimer formation between conjugated aromatic systems.
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http://dx.doi.org/10.1002/chem.201402182DOI Listing
August 2014

Selective P4 activation by an organometallic nickel(I) radical: formation of a dinuclear nickel(II) tetraphosphide and related di- and trichalcogenides.

Chem Commun (Camb) 2014 Jul 21;50(53):7014-6. Epub 2014 May 21.

University of Regensburg, Institute of Inorganic Chemistry, 93040 Regensburg, Germany.

The reaction of the 17e nickel(I) radical [CpNi(IDipp)] (1, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with P4 results in a nickel tetraphosphide [{CpNi(IDipp)}2(μ-η(1):η(1)-P4)] with a butterfly-P4(2-) ligand; related chalcogenides [{CpNi(IDipp)}2(μ-E2)] (E = S, Se, Te) and [{CpNi(IDipp)}2(μ-E3)] (E = S, Se) are formed with S8, Se∞ and Te∞.
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http://dx.doi.org/10.1039/c4cc02601bDOI Listing
July 2014
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