Publications by authors named "Justin N Cross"

33 Publications

Crystallographic characterization of (CHSiMe)U(BH).

Acta Crystallogr E Crystallogr Commun 2021 Apr 12;77(Pt 4):383-389. Epub 2021 Mar 12.

Department of Chemistry, University of California, Irvine, California 92697, USA.

New syntheses have been developed for the synthesis of (borohydrido-κ)tris-[η-(tri-methyl-sil-yl)cyclo-penta-dien-yl]uranium(IV), [U(BH)(CHSi)] or Cp'U(BH) (Cp' = CHSiMe) and its structure has been determined by single-crystal X-ray crystallography. This compound crystallized in the space group and the structure features three -coordinated Cp' rings and a -coordinated (BH) ligand.
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http://dx.doi.org/10.1107/S2056989021002425DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8025856PMC
April 2021

Origins of the odd optical observables in plutonium and americium tungstates.

Chem Sci 2019 Jul 21;10(26):6508-6518. Epub 2019 May 21.

Department of Physics and Astronomy , Aarhus University , 8000 , Aarhus C , Denmark . Email:

A series of trivalent f-block tungstates, MWO(OH)(HO) (M = La, Ce, Pr, Nd, and Pu) and AmWO(OH), have been prepared in crystalline form using hydrothermal methods. Both structure types take the form of 3D networks where MWO(OH)(HO) is assembled from infinite chains of distorted tungstate octahedra linked by isolated MO bicapped trigonal prisms; whereas AmWO(OH) is constructed from edge-sharing AmO square antiprisms connected by distorted tungstate trigonal bipyramids. PuWO(OH)(HO) crystallizes as red plates; an atypical color for a Pu(iii) compound. Optical absorption spectra acquired from single crystals show strong, broadband absorption in the visible region. A similar feature is observed for CeWO(OH)(HO), but not for AmWO(OH). Here we demonstrate that these significantly different optical properties do not stem directly from the 5f electrons, as in both systems the valence band has mostly O-2p character and the conduction band has mostly W-5d character. Furthermore, the quasi-particle gap is essentially unaffected by the 5f degrees of freedom. Despite this, our analysis demonstrates that the f-electron covalency effects are quite important and substantially different energetically in PuWO(OH)(HO) and AmWO(OH), indicating that the optical gap alone cannot be used to infer conclusions concerning the f electron contribution to the chemical bond in these systems.
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http://dx.doi.org/10.1039/c9sc01174aDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6610570PMC
July 2019

Advancing Understanding of the +4 Metal Extractant Thenoyltrifluoroacetonate (TTA); Synthesis and Structure of MTTA (M = Zr, Hf, Ce, Th, U, Np, Pu) and M(TTA) (M = Ce, Nd, Sm, Yb).

Inorg Chem 2018 Apr 21;57(7):3782-3797. Epub 2018 Mar 21.

University of New Mexico , Albuquerque , New Mexico 87131 , United States.

Thenoyltrifluoroacetone (HTTA)-based extractions represent popular methods for separating microscopic amounts of transuranic actinides (i.e., Np and Pu) from macroscopic actinide matrixes (e.g. bulk uranium). It is well-established that this procedure enables +4 actinides to be selectively removed from +3, + 5, and +6 f-elements. However, even highly skilled and well-trained researchers find this process complicated and (at times) unpredictable. It is difficult to improve the HTTA extraction-or find alternatives-because little is understood about why this separation works. Even the identities of the extracted species are unknown. In addressing this knowledge gap, we report here advances in fundamental understanding of the HTTA-based extraction. This effort included comparatively evaluating HTTA complexation with +4 and +3 metals (M = Zr, Hf, Ce, Th, U, Np, and Pu vs M = Ce, Nd, Sm, and Yb). We observed +4 metals formed neutral complexes of the general formula M(TTA). Meanwhile, +3 metals formed anionic M(TTA) species. Characterization of these M(TTA) ( x = 0, 1) compounds by UV-vis-NIR, IR, H and F NMR, single-crystal X-ray diffraction, and X-ray absorption spectroscopy (both near-edge and extended fine structure) was critical for determining that Np(TTA) and Pu(TTA) were the primary species extracted by HTTA. Furthermore, this information lays the foundation to begin developing and understanding of why the HTTA extraction works so well. The data suggest that the solubility differences between M(TTA) and M(TTA) are likely a major contributor to the selectivity of HTTA extractions for +4 cations over +3 metals. Moreover, these results will enable future studies focused on explaining HTTA extractions preference for +4 cations, which increases from Np to Pu, Hf, and Zr.
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http://dx.doi.org/10.1021/acs.inorgchem.7b03089DOI Listing
April 2018

Incipient class II mixed valency in a plutonium solid-state compound.

Nat Chem 2017 09 8;9(9):856-861. Epub 2017 May 8.

Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, Florida 32306, USA.

Electron transfer in mixed-valent transition-metal complexes, clusters and materials is ubiquitous in both natural and synthetic systems. The degree to which intervalence charge transfer (IVCT) occurs, dependent on the degree of delocalization, places these within class II or III of the Robin-Day system. In contrast to the d-block, compounds of f-block elements typically exhibit class I behaviour (no IVCT) because of localization of the valence electrons and poor spatial overlap between metal and ligand orbitals. Here, we report experimental and computational evidence for delocalization of 5f electrons in the mixed-valent Pu/Pu solid-state compound, Pu(DPA)(HO) (DPA = 2,6-pyridinedicarboxylate). The properties of this compound are benchmarked by the pure Pu and Pu dipicolinate complexes, [Pu(DPA)(HO)]Br and Pu(DPA)(HO)·3HO, as well as by a second mixed-valent compound, Pu[Pu(DPA)H], that falls into class I instead. Metal-to-ligand charge transfer is involved in both the formation of Pu(DPA)(HO) and in the IVCT.
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http://dx.doi.org/10.1038/nchem.2777DOI Listing
September 2017

Covalency in Americium(III) Hexachloride.

J Am Chem Soc 2017 06 14;139(25):8667-8677. Epub 2017 Jun 14.

Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.

Developing a better understanding of covalency (or orbital mixing) is of fundamental importance. Covalency occupies a central role in directing chemical and physical properties for almost any given compound or material. Hence, the concept of covalency has potential to generate broad and substantial scientific advances, ranging from biological applications to condensed matter physics. Given the importance of orbital mixing combined with the difficultly in measuring covalency, estimating or inferring covalency often leads to fiery debate. Consider the 60-year controversy sparked by Seaborg and co-workers ( Diamond, R. M.; Street, K., Jr.; Seaborg, G. T. J. Am. Chem. Soc. 1954 , 76 , 1461 ) when it was proposed that covalency from 5f-orbitals contributed to the unique behavior of americium in chloride matrixes. Herein, we describe the use of ligand K-edge X-ray absorption spectroscopy (XAS) and electronic structure calculations to quantify the extent of covalent bonding in-arguably-one of the most difficult systems to study, the Am-Cl interaction within AmCl. We observed both 5f- and 6d-orbital mixing with the Cl-3p orbitals; however, contributions from the 6d-orbitals were more substantial. Comparisons with the isoelectronic EuCl indicated that the amount of Cl 3p-mixing with Eu 5d-orbitals was similar to that observed with the Am 6d-orbitals. Meanwhile, the results confirmed Seaborg's 1954 hypothesis that Am 5f-orbital covalency was more substantial than 4f-orbital mixing for Eu.
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http://dx.doi.org/10.1021/jacs.7b03755DOI Listing
June 2017

Identification of the Formal +2 Oxidation State of Plutonium: Synthesis and Characterization of {Pu[CH(SiMe)]}.

J Am Chem Soc 2017 03 13;139(11):3970-3973. Epub 2017 Mar 13.

Department of Chemistry, University of California , Irvine, California 92697-2025, United States.

Over 70 years of chemical investigations have shown that plutonium exhibits some of the most complicated chemistry in the periodic table. Six Pu oxidation states have been unambiguously confirmed (0 and +3 to +7), and four different oxidation states can exist simultaneously in solution. We report a new formal oxidation state for plutonium, namely Pu in [K(2.2.2-cryptand)][PuCp″], Cp″ = CH(SiMe). The synthetic precursor PuCp″ is also reported, comprising the first structural characterization of a Pu-C bond. Absorption spectroscopy and DFT calculations indicate that the Pu ion has predominantly a 5f electron configuration with some 6d mixing.
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http://dx.doi.org/10.1021/jacs.7b00706DOI Listing
March 2017

Comparing the 2,2'-Biphenylenedithiophosphinate Binding of Americium with Neodymium and Europium.

Angew Chem Int Ed Engl 2016 10 15;55(41):12755-9. Epub 2016 Sep 15.

Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.

Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear-fuel cycles. Herein, we describe the preparation of (NBu4 )Am[S2 P((t) Bu2 C12 H6 )]4 and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., Nd(III) ) and an isoelectronic one (Eu(III) ). The results include the first measurement of an Am-S bond length, with a mean value of 2.921(9) Å, by single-crystal X-ray diffraction. Comparison with the Eu(III) and Nd(III) complexes revealed subtle electronic differences between the complexes of Am(III) and the lanthanides.
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http://dx.doi.org/10.1002/anie.201606367DOI Listing
October 2016

Spectroscopic and computational investigation of actinium coordination chemistry.

Nat Commun 2016 08 17;7:12312. Epub 2016 Aug 17.

Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.

Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, Ac(III) reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac-Cl and Ac-OH2O distances are measured to be 2.95(3) and 2.59(3) Å, respectively. The X-ray absorption spectroscopy comparisons between Ac(III) and Am(III) in HCl solutions indicate Ac(III) coordinates more inner-sphere Cl(1-) ligands (3.2±1.1) than Am(III) (0.8±0.3). These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique Ac(III) chemical behaviour.
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http://dx.doi.org/10.1038/ncomms12312DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4992055PMC
August 2016

Nuclear Magnetic Resonance Measurements and Electronic Structure of Pu(IV) in [(Me)4N]2PuCl6.

Inorg Chem 2016 Sep 11;55(17):8371-80. Epub 2016 Aug 11.

Los Alamos National Laboratory , Los Alamos, New Mexico 87544, United States.

The synthesis, electronic structure, and characterization via single-crystal X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, and magnetic susceptibility of (Me4N)2PuCl6 are reported. NMR measurements were performed to both search for the direct (239)Pu resonance and to obtain local magnetic and electronic information at the Cl site through (35)Cl and (37)Cl spectra. No signature of (239)Pu NMR was observed. The temperature dependence of the Cl spectra was simulated by diagonalizing the Zeeman and quadrupolar Hamiltonians for (35)Cl, (37)Cl, and (14)N isotopes. Electronic structure calculations predict a magnetic Γ5 triplet ground state of Pu(IV) in the crystalline electric field of the undistorted PuCl6 octahedron. A tetragonal distortion would result in a very small splitting (∼20 cm(-1)) of the triplet ground state into a nonmagnetic singlet and a doublet state. The Cl shifts have an inflection point at T ≈ 15 K, differing from the bulk susceptibility, indicating a nonmagnetic crystal field ground state. The Cl spin-lattice relaxation time is constant to T = 15 K, below which it rapidly increases, also supporting the nonmagnetic crystal field ground state.
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http://dx.doi.org/10.1021/acs.inorgchem.6b00735DOI Listing
September 2016

Coordination chemistry of 2,2'-biphenylenedithiophosphinate and diphenyldithiophosphinate with U, Np, and Pu.

Dalton Trans 2015 Nov;44(43):18923-36

Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.

New members of the dithiophosphinic acid family of potential actinide extractants were prepared: heterocyclic 2,2'-biphenylenedithiophosphinic acids of stoichiometry HS2P(R2C12H6) (R = H or (t)Bu). The time- and atom-efficient syntheses afforded multigram quantities of pure HS2P(R2C12H6) in reasonable yields (∼60%). These compounds differed from other diaryldithiophosphinic acid extractants in that the two aryl groups were connected to one another at the ortho positions to form a 5-membered dibenzophosphole ring. These 2,2'-biphenylenedithiophosphinic acids were readily deprotonated to form S2P(R2C12H6)(1-) anions, which were crystallized as salts with tetraphenylpnictonium cations (ZPh4(1+); Z = P or As). Coordination chemistry between [S2P((t)Bu2C12H6)](1-) and [S2P(C6H5)2](1-) with U, Np, and Pu was comparatively investigated. The results showed that dithiophosphinate complexes of U(IV) and Np(IV) were redox stable relative to those of U(III), whereas reactions involving Pu(IV) gave intractable material. For instance, reactions involving U(IV) and Np(IV) generated An[S2P((t)Bu2C12H6)]4 and An[S2P(C6H5)2]4 whereas reactions between Pu(IV) and [S2P(C6H5)2](1-) generated a mixture of products from which we postulated a transient Pu(III) species based on UV-Vis spectroscopy. However, the trivalent Pu[S2P(C6H5)2]3(NC5H5)2 compound is stable and could be isolated from reactions between [S2P(C6H5)2](1-) and the trivalent PuI3(NC5H5)4 starting material. Attempts to synthesize analogous trivalent compounds with U(III) provided the tetravalent U[S2P(C6H5)2]4 oxidation product.
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http://dx.doi.org/10.1039/c5dt02976gDOI Listing
November 2015

Why is uranyl formohydroxamate red?

Inorg Chem 2015 Jun 9;54(11):5280-4. Epub 2015 May 9.

†Department of Chemistry and Biochemistry, Florida State University, 102 Varsity Way, Tallahassee, Florida 32306, United States.

The complexation of UO2(2+) by formohydroxamate (FHA(-)) creates solutions with dark red coloration. The inherent redox activity of formohydroxamate leads to the possibility that these solutions contain U(V) complexes, which are often red. We demonstrate that the reaction of U(VI) with formohydroxamate does not result in reduction, but rather in formation of the putative cis-aquo UO2(FHA)2(H2O)2, whose polymeric solid-state structure, UO2(FHA)2, contains an unusually bent UO2(2+) unit and a highly distorted coordination environment around a U(VI) cation in general. The bending of the uranyl cation results from unusually strong π donation from the FHA(-) ligands into the 6d and 5f orbitals of the U(VI) cation. The alteration of the bonding in the uranyl unit drastically changes its electronic and vibrational features.
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http://dx.doi.org/10.1021/acs.inorgchem.5b00262DOI Listing
June 2015

Emergence of californium as the second transitional element in the actinide series.

Nat Commun 2015 Apr 16;6:6827. Epub 2015 Apr 16.

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.

A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of californium(II) is responsible for many of the unusual properties of californium including the green photoluminescence.
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http://dx.doi.org/10.1038/ncomms7827DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4410632PMC
April 2015

Ionothermal synthesis of tetranuclear borate clusters containing f- and p-block metals.

Inorg Chem 2015 Jan 2;54(2):570-5. Epub 2015 Jan 2.

Department of Chemistry and Biochemistry, Florida State University , 95 Chieftain Way, Tallahassee, Florida 32306, United States.

The reactions of simple oxides or halides of trivalent lanthanides and actinides or bismuth with boric acid in the ionic liquid 1-butyl-3-methylimidazolium chloride at 150 °C result in the formation and crystallization of a series of isomorphous tetranuclear borate clusters with the general formula M4B22O36(OH)6(H2O)13 (M = La, Ce, Pr, Nd, Sm, Eu, Gd, Pu, and Bi). These clusters do not assemble with trivalent cations smaller than Gd(3+), suggesting that the formation of the clusters is dictated by the size of the metal ion. The cations are found in cavities along the periphery of a cage assembled from the corner- and edge-sharing interactions of BO3 triangles and BO4 tetrahedra, yielding a complex chiral cluster. Both enantiomers cocrystallize. The metal ions are nonacoordinate, and their geometries are best described as distorted tridiminished icosahedra. This coordination environment is new for both Pu(3+) and Bi(3+). In addition to detailed structural information, UV/vis-NIR absorption and photoluminescence spectra are also provided.
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http://dx.doi.org/10.1021/ic502461dDOI Listing
January 2015

LnV₃Te₃O₁₅(OH)₃·nH₂O (Ln = Ce, Pr, Nd, Sm, Eu, Gd; n = 1-2): a new series of semiconductors with mixed-valent tellurium (IV,VI) oxoanions.

Inorg Chem 2014 Sep 21;53(17):9058-64. Epub 2014 Aug 21.

Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, Tallahassee, Florida 32306, United States.

Six new lanthanide tellurium vanadates with the general formula LnV3Te3O15(OH)3·nH2O (LnVTeO) (Ln = Ce, Pr, Nd, Sm, Eu, and Gd; n = 2 for Ce and Pr; n = 1 for Nd, Sm, Eu, and Gd) have been prepared hydrothermally via the reactions of lanthanide nitrates, TeO2, and V2O5 at 230 °C. LnVTeO adopts a three-dimensional (3D) channel structure with a space group of P63/mmc. Surprisingly, two types of oxoanions: Te(IV)O3(2-) trigonal pyramids and Te(VI)O6(6-) octahedra, coexist in these compounds. Solid-state UV-vis-NIR absorption spectra for LnVTeO show approximate band gaps on the order of 1.9 eV, suggesting the wide band gap semiconducting nature of these materials. No magnetic phase transition was observed in any of the analogues, but a clear increase in the strength of short-range antiferromagnetic correlations was found with the shortening of distances between magnetically coupled Ln(3+) ions in LnVTeO.
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http://dx.doi.org/10.1021/ic501068eDOI Listing
September 2014

Chirality and polarity in the f-block borates M4[B16O26(OH)4(H2O)3Cl4] (M = Sm, Eu, Gd, Pu, Am, Cm, and Cf).

Chemistry 2014 Aug 7;20(32):9892-6. Epub 2014 Jul 7.

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306 (USA).

The reactions of trivalent lanthanides and actinides with molten boric acid in high chloride concentrations result in the formation of M4[B16O26(OH)4(H2O)3Cl4] (M = Sm, Eu, Gd, Pu, Am, Cm, Cf). This cubic structure type is remarkably complex and displays both chirality and polarity. The polymeric borate network forms helical features that are linked via two different types of nine-coordinate f-element environments. The f-f transitions are unusually intense and result in dark coloration of these compounds with actinides.
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http://dx.doi.org/10.1002/chem.201403820DOI Listing
August 2014

Expansion of the rich structures and magnetic properties of neptunium selenites: soft ferromagnetism in Np(SeO3)2.

Inorg Chem 2014 Jul 25;53(14):7154-9. Epub 2014 Jun 25.

Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, 310 DLC, Tallahassee, Florida 32306, United States.

Two new neptunium selenites with different oxidation states of the metal centers, Np(IV)(SeO3)2 and Np(VI)O2(SeO3), have been synthesized under mild hydrothermal conditions at 200 °C from the reactions of NpO2 and SeO2. Np(SeO3)2 crystallizes as brown prisms (space group P21/n, a = 7.0089(5) Å, b = 10.5827(8) Å, c = 7.3316(5) Å, β = 106.953(1)°); whereas NpO2(SeO3) crystals are garnet-colored with an acicular habit (space group P21/m, a = 4.2501(3) Å, b = 9.2223(7) Å, c = 5.3840(4) Å, β = 90.043(2)°). Single-crystal X-ray diffraction studies reveal that the structure of Np(SeO3)2 features a three-dimensional (3D) framework consisting of edge-sharing NpO8 units that form chains that are linked via SeO3 units to create a 3D framework. NpO2(SeO3) possesses a lamellar structure in which each layer is composed of NpO8 hexagonal bipyramids bridged via SeO3(2-) anions. Bond-valence sum calculations and UV-vis-NIR absorption spectra support the assignment of tetravalent and hexavalent states of neptunium in Np(SeO3)2 and NpO2(SeO3), respectively. Magnetic susceptibility data for Np(SeO3)2 deviates substantially from typical Curie-Weiss behavior, which can be explained by large temperature-independent paramagnetic (TIP) effects. The Np(IV) selenite shows weak ferromagnetic ordering at 3.1(1) K with no detectable hysteresis, suggesting soft ferromagnetic behavior.
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http://dx.doi.org/10.1021/ic500181tDOI Listing
July 2014

Straightforward reductive routes to air-stable uranium(III) and neptunium(III) materials.

Inorg Chem 2014 Jul 25;53(14):7455-66. Epub 2014 Jun 25.

Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, 310 DLC, Tallahassee, Florida 32306-4390, United States.

Studies of trivalent uranium (U(3+)) and neptunium (Np(3+)) are restricted by the tendency of these ions to oxidize in the presence of air and water, requiring manipulations to be carried out in inert conditions to produce trivalent products. While the organometallic and high-temperature reduction chemistry of U(3+) and, to a much smaller extent, Np(3+) has been explored, the study of the oxoanion chemistry of these species has been limited despite their interesting optical and magnetic properties. We report the synthesis of U(3+) and Np(3+) sulfates by utilizing zinc amalgam as an in situ reductant with absolutely no regard to the exclusion of O2 or water. By employing this method we have developed a family of alkali metal U(3+) and Np(3+) sulfates that are air and water stable. The structures, electronic spectra, and magnetic behavior are reported.
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http://dx.doi.org/10.1021/ic500771tDOI Listing
July 2014

Further evidence for the stabilization of U(V) within a tetraoxo core.

Inorg Chem 2014 May 1;53(10):5294-9. Epub 2014 May 1.

Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, Tallahassee, Florida 32306-4390, United States.

Two complex layered uranyl borates, K10[(UO2)16(B2O5)2(BO3)6O8]·7H2O (1) and K13[(UO2)19(UO4)(B2O5)2(BO3)6(OH)2O5]·H2O (2), were isolated from supercritical water reactions. Within these compounds, borate exists only as BO3 units and is found as either isolated BO3 triangles or B2O5 dimers, the latter being formed from corner sharing of two BO3 units. These anions, along with oxide and hydroxide, bridge between uranyl centers to create the complex layers in these compounds. U(VI) cations are found within uranyl, UO2(2+) units, that are bound by four or five oxygen atoms to create tetragonal and pentagonal bipyramidal environments. The most striking feature in this system is found in 2, where a [UO4(OH)2] unit exists that contains U(V) within a tetraoxo core with trans hydroxide anions; therefore, this compound is a mixed-valent U(VI)/U(V) borate. The presence of a 5f(1) uranium site within 2 leads to unusual optical properties.
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http://dx.doi.org/10.1021/ic500523aDOI Listing
May 2014

Unusual structure, bonding and properties in a californium borate.

Nat Chem 2014 May 23;6(5):387-92. Epub 2014 Mar 23.

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.

The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations demonstrated the involvement of 6p, 6d and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. Here we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and substantially rearrange on complexation. A ligand that suits both of these desired properties is polyborate. We demonstrate that the 5f, 6d and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal-field effects are present. Synthetic, structural and spectroscopic data are complemented by quantum mechanical calculations to support these observations.
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http://dx.doi.org/10.1038/nchem.1896DOI Listing
May 2014

Synthesis and spectroscopy of new plutonium(III) and -(IV) molybdates: comparisons of electronic characteristics.

Inorg Chem 2014 Mar 6;53(6):3148-52. Epub 2014 Mar 6.

Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, 310 DLC, Tallahassee, Florida 32306-4390, United States.

Synthesis of a plutonium(III) molybdate bromide, PuMoO4Br(H2O), has been accomplished using hydrothermal techniques in an inert-atmosphere glovebox. The compound is green in color, which is in stark contrast to the typical blue color of plutonium(III) complexes. The unusual color arises from the broad charge transfer (CT) spanning from approximately 300 to 500 nm in the UV-vis-near-IR spectra. Repeating the synthesis with an increase in the reaction temperature results in the formation of a plutonium(IV) molybdate, Pu3Mo6O24(H2O)2, which also has a broad CT band and red-shifted f-f transitions. Performing an analogous reaction with neodymium produced a completely different product, [Nd(H2O)3][NdMo12O42]·2H2O, which is built of Silverton-type polyoxometallate clusters.
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http://dx.doi.org/10.1021/ic403116rDOI Listing
March 2014

Th(VO3)2(SeO3) and Ln(VO3)2(IO3) (Ln = Ce, Pr, Nd, Sm, and Eu): unusual cases of aliovalent substitution.

Chem Commun (Camb) 2014 Apr;50(28):3668-70

Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, 310 DLC, Tallahassee, Florida 32306, USA.

Th(VO3)2(SeO3) and Ln(VO3)2(IO3) (Ln = Ce, Pr, Nd, Sm, and Eu) have been prepared and characterized. Surprisingly, these compounds are isotypic and rather extreme examples of aliovalent substitution (Th(IV)vs. Ln(III); Se(IV)O3(2-)vs. I(V)O3(-)) are possible in this structure type.
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http://dx.doi.org/10.1039/c4cc00537fDOI Listing
April 2014

Thermochromism, the Alexandrite effect, and dynamic Jahn-Teller distortions in Ho2Cu(TeO3)2(SO4)2.

Inorg Chem 2013 Nov 1;52(22):13278-81. Epub 2013 Nov 1.

Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, 310 DLC, Tallahassee, Florida 32306, United States.

A 3d-4f heterobimetallic material with mixed anions, Ho2Cu(TeO3)2(SO4)2, has been prepared under hydrothermal conditions. Ho2Cu(TeO3)2(SO4)2 exhibits both thermochromism and the Alexandrite effect. Variable temperature single crystal X-ray diffraction and UV-vis-NIR spectroscopy reveal that changes in the Cu(II) coordination geometry result in negative thermal expansion of axial Cu-O bonds that plays a role in the thermochromic transition of Ho2Cu(TeO3)2(SO4)2. Magnetic studies reveal an effective magnetic moment of 14.97 μB. which has a good agreement with the calculated value of 15.09 μB.
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http://dx.doi.org/10.1021/ic402432qDOI Listing
November 2013

Synthesis of divalent europium borate via in situ reductive techniques.

Inorg Chem 2013 Jul 3;52(14):8099-105. Epub 2013 Jul 3.

Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.

A new divalent europium borate, Eu[B8O11(OH)4], was synthesized by two different in situ reductive methodologies starting with a trivalent europium starting material in a molten boric acid flux. The two in situ reductive techniques employed were the use of HI as a source of H2 gas and the use of a Zn amalgam as a reductive, reactive surface. While both of these are known reductive techniques, the title compound was synthesized in both air and water which demonstrates that strict anaerobic conditions need not be employed in conjunction with these reductive methodologies. Herein, we report on the structure, spectroscopy, and synthetic methodologies relevant to Eu[B8O11(OH)4]. We also report on a europium doping study of the isostructural compound Sr[B8O11(OH)4] where the amount of doped Eu(2+) ranges from 2.5 to 11%.
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http://dx.doi.org/10.1021/ic400781xDOI Listing
July 2013

Comparisons of plutonium, thorium, and cerium tellurite sulfates.

Inorg Chem 2013 Apr 25;52(8):4277-81. Epub 2013 Mar 25.

Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, 310 DLC, Tallahassee, Florida 32306, United States.

The hydrothermal reaction of PuCl3 or CeCl3 with TeO2 in the presence of sulfuric acid under the comparable conditions results in the crystallization of Pu(TeO3)(SO4) or Ce2(Te2O5)(SO4)2, respectively. Pu(TeO3)(SO4) and its isotypic compound Th(TeO3)(SO4) are characterized by a neutral layer structure with no interlamellar charge-balancing ions. However, Ce2(Te2O5)(SO4)2 possesses a completely different dense three-dimensional framework. Bond valence calculation and UV-vis-NIR spectra indicate that the Ce compound is trivalent whereas the Pu and Th compounds are tetravalent leading to the formation of significantly different compounds. Pu(TeO3)(SO4), Th(TeO3)(SO4), and Ce2(Te2O5)(SO4)2 represent the first plutonium/thorium/cerium tellurite sulfate compounds. Our study strongly suggests that the chemistries of Pu and Ce are not the same, and this is another example of the failure of Ce as a surrogate.
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http://dx.doi.org/10.1021/ic302216yDOI Listing
April 2013

From yellow to black: dramatic changes between cerium(IV) and plutonium(IV) molybdates.

J Am Chem Soc 2013 Feb 11;135(7):2769-75. Epub 2013 Feb 11.

Department of Chemistry and Biochemistry, University of Notre Dame, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, Indiana 46556, USA.

Hydrothermal reactions of CeCl(3) and PuCl(3) with MoO(3) and Cs(2)CO(3) yield surprisingly different results. Ce(3)Mo(6)O(24)(H(2)O)(4) crystallizes as bright yellow plates (space group C2/c, a = 12.7337(7) Å, b = 22.1309(16) Å, c = 7.8392(4) Å, β = 96.591(4)°, V = 2194.6(2) Å(3)), whereas CsPu(3)Mo(6)O(24)(H(2)O) crystallizes as semiconducting black-red plates (space group C2/c, a = 12.633(5) Å, b = 21.770(8) Å, c = 7.743(7) Å, β = 96.218(2)°, V = 2117(2) Å(3)). The topologies of the two compounds are similar, with channel structures built from disordered Mo(VI) square pyramids and (RE)O(8) square antiprisms (RE = Ce(IV), Pu(IV)). However, the Pu(IV) compound contains Cs(+) in its channels, while the channels in Ce(3)Mo(6)O(24)(H(2)O)(4) contain water molecules. Disorder and an ambiguous oxidation state of Mo lead to the formula CsPu(3)Mo(6)O(24)(H(2)O), where one Mo site is Mo(V) and the rest are Mo(VI). X-ray absorption near-edge structure (XANES) experiments were performed to investigate the source of the black color of CsPu(3)Mo(6)O(24)(H(2)O). These experiments revealed Pu to be tetravalent, while the strong pre-edge absorption from the distorted molybdate anions leaves the oxidation state ambiguous between Mo(V) and Mo(VI).
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http://dx.doi.org/10.1021/ja311910hDOI Listing
February 2013

A new family of lanthanide borate halides with unusual coordination and a new neodymium-containing cationic framework.

Inorg Chem 2013 Feb 29;52(4):1965-75. Epub 2013 Jan 29.

Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.

The reactions of Ln(2)O(3)/CeO(2)/Pr(6)O(11) (Ln = La-Nd, Sm), molten boric acid, and concentrated HBr or HI result in the formation of La[B(7)O(10)(OH)(3)(H(2)O)Br], Ln[B(6)O(9)(OH)(2)(H(2)O)(2)Br]·0.5H(2)O (Ln = Ce, Pr), Nd(2)[B(12)O(17.5)(OH)(5)(H(2)O)(4)Br(1.5)]Br(0.5)·H(2)O (NdBOBr), Sm(4)[B(18)O(25)(OH)(13)Br(3)], and Ln[B(7)O(11)(OH)(H(2)O)(3)I] (Ln = La-Nd, Sm). The lanthanide(III) centers in these compounds are found with 9-coordinate hula hoop or 10-coordinate capped triangular cupola geometries, where there are six approximately coplanar oxygen donors provided by the polyborate sheet. The sheets are formed into three-dimensional frameworks via BO(3) triangles that are roughly perpendicular to the layers. Additionally, a new cationic framework, NdBOBr, has been isolated. NdBOBr is unusual in that not only is it a cationic framework, but it is also the first trivalent f-element borate to have terminal halides bound exclusively to the base site of the hula hoop. The Ln[B(7)O(11)(OH)(H(2)O)(3)I] (Ln = La-Nd, Sm) structures require two corner-shared BO(3) units in order to tether the layers together because of the large size of the capping iodine atom.
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http://dx.doi.org/10.1021/ic302309zDOI Listing
February 2013

Unusual coordination for plutonium(IV), cerium(IV), and zirconium(IV) in the cationic layered materials [M2Te4O11]X2 (M = Pu, Ce, Zr; X = Cl, Br).

Inorg Chem 2012 Nov 17;51(21):11949-54. Epub 2012 Oct 17.

Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, Notre Dame, Indiana 46556, USA.

Four isotypic cationic layered materials, [Pu(2)Te(4)O(11)]Cl(2), [Ce(2)Te(4)O(11)]Cl(2), [Zr(2)Te(4)O(11)]Cl(2), and [Zr(2)Te(4)O(11)]Br(2), have been prepared under hydrothermal conditions. Single crystal diffraction studies reveal that these materials possess cationic Pu/Ce/Zr tellurite layers with halides as interlamellar charge-balancing anions. The Pu(IV), Ce(IV), and Zr(IV) centers of the cationic layers exhibit a quite rare pentagonal bipyramid coordination environment.
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http://dx.doi.org/10.1021/ic301846gDOI Listing
November 2012

Effect of pH and reaction time on the structures of early lanthanide(III) borate perchlorates.

Inorg Chem 2012 Nov 9;51(21):11541-8. Epub 2012 Oct 9.

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.

Reactions of LnCl(3)·6H(2)O (Ln = La-Nd, Sm, Eu), concentrated (11 M) perchloric acid, and molten boric acid result in the formation of four different compounds. These compounds are Ln[B(8)O(10)(OH)(6)(H(2)O)(ClO(4))]·0.5H(2)O (Ln = La-Nd, Sm), Pr[B(8)O(11)(OH)(4)(H(2)O)(ClO(4))], Ln[B(7)O(11)(OH)(H(2)O)(2)(ClO(4))] (Ln = Pr, Nd, Sm, and Eu), and Ce[B(8)O(11)(OH)(4)(H(2)O)(ClO(4))]. All Ln(III) cations are ten-coordinate with a capped triangular cupola geometry and contain an inner-sphere, monodentate perchlorate moiety. This geometry is obtained because of the coordination of the oxygen donors within the polyborate sheet which create triangular holes and provide residence for the lanthanide metal centers. Aside from Ln[B(8)O(10)(OH)(6)(H(2)O)(ClO(4))]·0.5H(2)O (Ln = La-Nd, Sm), which are two-dimensional sheet structures, all other compounds are three-dimensional frameworks in which the layers are tethered together by BO(3) units found roughly perpendicular to the sheets. Furthermore, a change in product is observed depending on the reaction duration while holding all other synthetic variables constant. This report also demonstrates that lanthanide borates can be prepared in extreme acidic conditions.
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http://dx.doi.org/10.1021/ic301421eDOI Listing
November 2012

Cerium(IV) tellurite halides [Ce2Te7O17]X2 (X = Cl- or Br-): the first cerium-containing cationic frameworks.

Inorg Chem 2012 Oct 19;51(19):10083-5. Epub 2012 Sep 19.

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.

Two isotypic cerium tellurite halides with the formulas [Ce(2)Te(7)O(17)]Cl(2) and [Ce(2)Te(7)O(17)]Br(2) have been synthesized hydrothermally via the reactions of CeCl(3) and CeBr(3) with TeO(2). The structures of these compounds feature a cationic inorganic framework. The Ce(IV) dimers are bound by a novel 3D Te(7)O(17)(6-) building unit, forming an unusual hexagonal-bipyramidal environment around Ce(IV).
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http://dx.doi.org/10.1021/ic301628qDOI Listing
October 2012

A magnetic resonance imaging contrast agent capable of detecting hydrogen peroxide.

Inorg Chem 2012 Sep 13;51(17):9153-5. Epub 2012 Aug 13.

Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States.

The redox-active ligand N-(2-hydroxy-5-methylbenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (Hptp1) was prepared and complexed to manganese(II). The isolated [Mn(Hptp1)(MeCN)](2+) serves as a magnetic resonance imaging contrast agent, with an r(1) value comparable to those of other mononuclear gadolinium(III) and manganese(II) complexes. The metal and ligand are stable in aerated aqueous solutions, but the addition of H(2)O(2) causes the complex to oxidatively couple to itself through a bimolecular reaction involving the phenol groups of two Hptp1 ligands. The binuclear product is less paramagnetic per manganese(II) than its mononuclear precursor, lowering the measured r(1) per manganese(II). The manganese(II) complex with Hptp1 can thereby serve as a sensor for oxidative stress.
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http://dx.doi.org/10.1021/ic3012603DOI Listing
September 2012