Publications by authors named "Alankriti Bajpai"

16 Publications

  • Page 1 of 1

The "Chemistree" of Porous Coordination Networks: Taxonomic Classification of Porous Solids to Guide Crystal Engineering Studies.

Small 2021 06 10;17(22):e2006351. Epub 2021 Mar 10.

Department of Chemical Sciences and, Bernal Institute, University of Limerick, Limerick, V94 T9PX, Republic of Ireland.

New approaches to gas/vapor storage and purification are urgently needed to address the large energy footprint, cost, and/or risk associated with existing technologies. In this context, new classes of porous physisorbents, exemplified by porous coordination networks (PCNs), have emerged. There are now >100 000 entries in the Cambridge Structural Database (CSD) metal-organic framework (MOF) subset and the rate of publication, >5000 per year, grows unabatedly. The number of PCNs makes it infeasible to test all of them for sorption performance and it is therefore timely to introduce a classification approach based upon taxonomy to supplement topological classification of PCNs. This taxonomic approach complements existing databases such as the CSD and enable the design (crystal engineering) of new families of PCNs. It also categorizes existing PCNs in a manner useful to crystal engineers. The internal consistency of the taxonomic approach is verified by case studies of several well-known PCNs whereas its utility is demonstrated upon understudied topologies and hard-to-rationalize infinite rod building blocks. Overall, taxonomic classification enables a traffic light system to direct crystal engineers towards finding a "needle in haystack," that is, a family (platform) of PCNs that is amenable to crystal engineering and systematic structure/property studies.
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http://dx.doi.org/10.1002/smll.202006351DOI Listing
June 2021

Highly Selective, High-Capacity Separation of o-Xylene from C Aromatics by a Switching Adsorbent Layered Material.

Angew Chem Int Ed Engl 2019 May 9;58(20):6630-6634. Epub 2019 Apr 9.

Department of Chemical Sciences, Bernal Institute, University of Limerick, Limerick, Republic of Ireland.

Purification of the C aromatics (xylenes and ethylbenzene) is particularly challenging because of their similar physical properties. It is also relevant because of their industrial utility. Physisorptive separation of C aromatics has long been suggested as an energy efficient solution but no physisorbent has yet combined high selectivity (>5) with high adsorption capacity (>50 wt %). Now a counterintuitive approach to the adsorptive separation of o-xylene from other C aromatics involves the study of a known nonporous layered material, [Co(bipy) (NCS) ] (sql-1-Co-NCS), which can reversibly switch to C aromatics loaded phases with different switching pressures and kinetics, manifesting benchmark o-xylene selectivity (S ≈60) and high saturation capacity (>80 wt %). Structural insight into the observed selectivity and capacity is gained by analysis of the crystal structures of C aromatics loaded phases.
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http://dx.doi.org/10.1002/anie.201901198DOI Listing
May 2019

Modulation of Excited-State Proton-Transfer Dynamics inside the Nanocavity of Microheterogeneous Systems: Microenvironment-Sensitive Förster Energy Transfer to Riboflavin.

Chemphyschem 2019 Mar 28;20(6):881-889. Epub 2019 Feb 28.

Department of Organic Chemistry, Indian Institute of Science, Bangalore, 560012, India.

The excited-state proton-transfer efficiency of a tetraarylpyrene derivative, 1,3,6,8-tetrakis(4-hydroxy-2,6-dimethylphenyl)pyrene (TDMPP), was investigated thoroughly in the presence of various surfactant assemblies, such as micelles and vesicles. The confined microheterogeneous environments can significantly retard the extent of the excited-state proton-transfer process, resulting in a distinguishable optical signal compared to that in the bulk medium. Physical characteristics of the surfactant assemblies, such as order, interfacial hydration, and surface charge, influence the proton transfer process and allow multiparametric sensing. A higher degree of interfacial hydration facilitates the proton-transfer process, while the positively charged head groups of the surfactants specifically stabilize the anionic form of the probe (TDMPP-O*). Furthermore, Forster energy transfer from the probe to riboflavin was studied in a phospholipid membrane, wherein the relative ratio of the neutral versus anionic forms (TDMPP-OH/TDMPP-O*) was found to influence the extent of energy transfer. Overall, we demonstrate how an ultrafast photophysical process, that is, the excited-state proton transfer, can be influenced by the microenvironment.
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http://dx.doi.org/10.1002/cphc.201801085DOI Listing
March 2019

A dynamic and multi-responsive porous flexible metal-organic material.

Nat Commun 2018 08 6;9(1):3080. Epub 2018 Aug 6.

Department of Chemical Sciences, Bernal Institute, University of Limerick, Limerick, V94 T9PX, Ireland.

Stimuli responsive materials (SRMs) respond to environmental changes through chemical and/or structural transformations that can be triggered by interactions at solid-gas or solid-liquid interfaces, light, pressure or temperature. SRMs span compositions as diverse as organic polymers and porous inorganic solids such as zeolites. Metal-organic materials (MOMs), sustained by metal nodes and organic linker ligands are of special interest as SRMs. SR-MOMs have thus far tended to exhibit only one type of transformation, e.g. breathing, in response to one stimulus, e.g. pressure change. We report [Zn(4,4'-biphenyldicarboxylate)(4,4'-bis(4-pyridyl)biphenyl)], an SR-MOM, which exhibits six distinct phases and four types of structural transformation in response to various stimuli. The observed structural transformations, breathing, structural isomerism, shape memory effect, and change in the level of interpenetration, are previously known individually but have not yet been reported to exist collectively in the same compound. The multi-dynamic nature of this SR-MOM is mainly characterised by using in-situ techniques.
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http://dx.doi.org/10.1038/s41467-018-05503-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6079025PMC
August 2018

Readily accessible shape-memory effect in a porous interpenetrated coordination network.

Sci Adv 2018 04 27;4(4):eaaq1636. Epub 2018 Apr 27.

Department of Chemical Sciences, Bernal Institute, University of Limerick, Limerick, Republic of Ireland.

Shape-memory effects are quite well-studied in general, but there is only one reported example in the context of porous materials. We report the second example of a porous coordination network that exhibits a sorbate-induced shape-memory effect and the first in which multiple sorbates, N, CO and CO promote this effect. The material, a new threefold interpenetrated pcu network, [Zn(4,4'-biphenyldicarboxylate)(1,4-bis(4-pyridyl)benzene)] (X-pcu-3-Zn-3i), exhibits three distinct phases: the as-synthesized α phase; a denser-activated β phase; and a shape-memory γ phase, which is intermediate in density between the α and β phases. The γ phase is kinetically stable over multiple adsorption/desorption cycles and only reverts to the β phase when heated at >400 K under vacuum. The α phase can be regenerated by soaking the γ phase in ,'-dimethylformamide. Single-crystal x-ray crystallography studies of all three phases provide insight into the shape-memory phenomenon by revealing the nature of interactions between interpenetrated networks. The β and γ phases were further investigated by in situ coincidence powder x-ray diffraction, and their sorption isotherms were replicated by density functional theory calculations. Analysis of the structural information concerning the three phases of X-pcu-3-Zn-3i enabled us to understand structure-function relationships and propose crystal engineering principles for the design of more examples of shape-memory porous materials.
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http://dx.doi.org/10.1126/sciadv.aaq1636DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5922793PMC
April 2018

The effect of centred versus offset interpenetration on CH sorption in hybrid ultramicroporous materials.

Chem Commun (Camb) 2017 Oct;53(84):11592-11595

Department of Chemical Sciences and Bernal Institute, University of Limerick, Republic of Ireland.

Fine-tuning of hybrid ultramicroporous materials (HUMs) can significantly impact their gas sorption performance. This study reveals that offset interpenetration can be antagonistic with respect to CH separation from CH/CH gas mixtures.
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http://dx.doi.org/10.1039/c7cc05882aDOI Listing
October 2017

Influence of Cations on the Fluorescence Quenching of an Ionic, Sterically Congested Pyrenyl Moiety by Iodide in Water.

J Phys Chem A 2017 Oct 27;121(40):7588-7596. Epub 2017 Sep 27.

Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.

Quenching of the excited singlet states of a water-soluble, sterically congested tetraarylpyrene, 1,3,6,8-tetrakis(2,6-dimethyl-4-(α-carboxy)methoxyphenyl)pyrene (Py4C), by a series of iodide salts has been investigated by steady-state and time-resolved fluorescence measurements. Access to the pyrenyl group of Py4C is restricted sterically as a result of the four flanking (2,6-dimethylphenoxy)acetic acid groups and the energy costs associated with their rotation. Deprotonation of the carboxylic acid groups of Py4C permits examination of ion-ion electrostatic interactions on the rates of quenching by iodide salts in which different steric and electrostatic factors are introduced by varying the cationic portions. At the same concentrations and with the same cations, chloride anions are ineffective quenchers. The quenching rate constants of Py4C by iodide are found to correlate linearly with the ionic radii of the cations and their enthalpies of hydration. These correlations are discussed in terms of the Hofmeister series. Furthermore, the results indicate that the cations that flank Py4C decrease the quenching efficiency of iodide through polarization and shielding effects (i.e., lowering the effective charge), which isolate to varying degrees the π-system. The effects of the different cations on quenching the fluorescence of a simpler and sterically unencumbered pyrenyl derivative, 1-pyrenylbutyric acid (PyBu), by iodide are much smaller. Overall, the results with Py4C indicate that the fluorescence quenching efficiency by iodide is influenced by direct interactions with the cations associated with the carboxylate groups of Py4C and not the solvation of water molecules. This observation is germane to a topic of current debate: Are the effects of the cations more closely related to bulk water properties or to direct ion-ion interactions? The conclusions obtained from these studies are applicable clearly to a wide variety of other systems in which ion pairing influences cooperative or inhibitory interactions.
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http://dx.doi.org/10.1021/acs.jpca.7b07853DOI Listing
October 2017

The role of weak interactions in controlling the mode of interpenetration in hybrid ultramicroporous materials.

Chem Commun (Camb) 2017 Apr;53(28):3978-3981

Department of Chemical Sciences and Bernal Institute, University of Limerick, Castletroy, Co. Limerick, Ireland.

The aromatic core in dipyridyl linker ligands is found to impact the mode of 2-fold interpenetration in hybrid ultramicroporous materials formed by pillared square grid networks. An analysis of the crystal structures suggests that linker conformation and weak interactions between the linkers in adjacent networks might explain this phenomenon.
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http://dx.doi.org/10.1039/c6cc10217dDOI Listing
April 2017

Highly Selective Separation of CH from CO by a New Dichromate-Based Hybrid Ultramicroporous Material.

ACS Appl Mater Interfaces 2017 Oct 27;9(39):33395-33400. Epub 2017 Jan 27.

Bernal Institute, Department of Chemical Sciences, University of Limerick , Limerick, Republic of Ireland.

A new hybrid ultramicroporous material, [Ni(1,4-di(pyridine-2-yl)benzene)(CrO)] (DICRO-4-Ni-i), has been prepared and structurally characterized. Pure gas sorption isotherms and molecular modeling of sorbate-sorbent interactions imply strong selectivity for CH over CO (S). Dynamic gas breakthrough coupled with temperature-programmed desorption experiments were conducted on DICRO-4-Ni-i and two other porous materials reported to exhibit high S, TIFSIX-2-Cu-i and MIL-100(Fe), using a CH/CO/He (10:5:85) gas mixture. Whereas CO/CH coadsorption by MIL-100(Fe) mitigated the purity of trapped CH, negligible coadsorption and high S were observed for DICRO-4-Ni-i and TIFSIX-2-Cu-i.
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http://dx.doi.org/10.1021/acsami.6b15250DOI Listing
October 2017

New Insights into an Old Problem. Fluorescence Quenching of Sterically-Graded Pyrenes by Tertiary Aliphatic Amines.

J Phys Chem A 2017 Jan 9;121(2):458-470. Epub 2017 Jan 9.

Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.

Although the quenching of singlet-excited states of aromatic molecules by amines has been studied for several decades, important aspects of the mechanism(s) remain nebulous. To address some of the unknowns, steric, and electronic factors associated with the quenching of the singlet-excited states of three electronically related aromatic molecules, pyrene, 1,3,6,8-tetraphenylpyrene (TPPy), and 1,3,6,8-tetrakis(4-methoxy-2,6-dimethylphenyl)pyrene (PyOMe), by a wide range of tertiary aliphatic amines have been assessed quantitatively. Correlations among the steric and electronic properties of the amines and the pyrenes (e.g., sizes, shapes, conformational labilities, excitation energies, and oxidation or reduction potentials) have been used in conjunction with the steady-state and dynamic fluorescence quenching data and DFT calculations on the ground and excited state complexes to make quantitative assessments of the steric and electronic factors controlling the quenching processes. PyOMe is a rather rigid bowl-like molecule that, in its electronic ground state, does not make stable complexes with amines in solution. TPPy has a shallower bowl-like shape that is much more flexible. Experiments conducted with a crystalline ground-state complex of an amine and PyOMe demonstrate (as assumed in many other studies but not shown conclusively heretofore) that the geometry needed for quenching the excited singlet state of PyOMe must place the lone-pair of electrons of the amines over the π-system of the pyrenyl group. Furthermore, there is a significant dependence on the shape and size of the amine on its ability to quench PyOMe, but not on the less conformationally constrained TPPy. The conclusions obtained from these studies are clearly applicable to a wide variety of other systems in which fluorescence from an aromatic moiety is being quenched, and they provide insights into how weak host-guest pairs interact.
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http://dx.doi.org/10.1021/acs.jpca.6b11382DOI Listing
January 2017

Flue-gas and direct-air capture of CO2 by porous metal-organic materials.

Philos Trans A Math Phys Eng Sci 2017 Jan;375(2084)

Bernal Institute, Department of Chemical Sciences, University of Limerick, Plassey House, Castletroy, Limerick, Republic of Ireland

Sequestration of CO, either from gas mixtures or directly from air (direct air capture), is a technological goal important to large-scale industrial processes such as gas purification and the mitigation of carbon emissions. Previously, we investigated five porous materials, three porous metal-organic materials (MOMs), a benchmark inorganic material, ZEOLITE 13X: and a chemisorbent, TEPA-SBA-15: , for their ability to adsorb CO directly from air and from simulated flue-gas. In this contribution, a further 10 physisorbent materials that exhibit strong interactions with CO have been evaluated by temperature-programmed desorption for their potential utility in carbon capture applications: four hybrid ultramicroporous materials, SIFSIX-3-CU: , DICRO-3-NI-I: , SIFSIX-2-CU-I: and MOOFOUR-1-NI: ; five microporous MOMs, DMOF-1: , ZIF-8: , MIL-101: , UIO-66: and UIO-66-NH2: ; an ultramicroporous MOM, NI-4-PYC: The performance of these MOMs was found to be negatively impacted by moisture. Overall, we demonstrate that the incorporation of strong electrostatics from inorganic moieties combined with ultramicropores offers improved CO capture performance from even moist gas mixtures but not enough to compete with chemisorbents.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.
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http://dx.doi.org/10.1098/rsta.2016.0025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5179930PMC
January 2017

Towards an understanding of the propensity for crystalline hydrate formation by molecular compounds.

IUCrJ 2016 Nov 18;3(Pt 6):430-439. Epub 2016 Oct 18.

Department of Chemical Sciences, Bernal Institute, University of Limerick , Co. Limerick, Ireland.

Hydrates are technologically important and ubiquitous yet they remain a poorly understood and understudied class of molecular crystals. In this work, we attempt to rationalize propensity towards hydrate formation through crystallization studies of molecules that lack strong hydrogen-bond donor groups. A Cambridge Structural Database (CSD) survey indicates that the statistical occurrence of hydrates in 124 molecules that contain five- and six-membered -heterocyclic aromatic moieties is 18.5%. However, hydrate screening experiments on a library of 11 -heterocyclic aromatic compounds with at least two acceptor moieties and no competing hydrogen-bond donors or acceptors reveals that over 70% of this group form hydrates, suggesting that extrapolation from CSD statistics might, at least in some cases, be deceiving. Slurrying in water and exposure to humidity were found to be the most effective discovery methods. Electrostatic potential maps and/or analysis of the crystal packing in anhydrate structures was used to rationalize why certain molecules did not readily form hydrates.
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http://dx.doi.org/10.1107/S2052252516015633DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5094445PMC
November 2016

Novel mode of 2-fold interpenetration observed in a primitive cubic network of formula [Ni(1,2-bis(4-pyridyl)acetylene)2(Cr2O7)]n.

Chem Commun (Camb) 2015 Oct;51(80):14832-5

Department of Chemical and Environmental Science, Materials and Surface Science Institute, University of Limerick, Republic of Ireland.

A primitive cubic (pcu) network of formula [Ni(1,2-bis(4-pyridyl)acetylene)2(Cr2O7)]n, , has been synthesised and found to exhibit a novel type of inclined 2-fold interpenetration and an isosteric heat of adsorption (Q(st)) of 30.5 kJ mol(-1) towards CO2 at zero loading. Q(st) is relatively high in the broad context but less than that observed in related hybrid ultramicroporous materials, a feature that can be understood after studying pore structure and molecular simulations of CO2 adsorption.
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http://dx.doi.org/10.1039/c5cc05866jDOI Listing
October 2015

A fluorescent paramagnetic Mn metal-organic framework based on semi-rigid pyrene tetra-carboxylic acid: sensing of solvent polarity and explosive nitroaromatics.

IUCrJ 2015 Sep 14;2(Pt 5):552-62. Epub 2015 Aug 14.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

An Mn metal-organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt's solvent polarity parameter (E T (N)). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.
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http://dx.doi.org/10.1107/S2052252515012506DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4547823PMC
September 2015

Single crystal-to-single crystal site-selective postsynthetic metal exchange in a Zn-MOF based on semi-rigid tricarboxylic acid and access to bimetallic MOFs.

Chemistry 2015 Feb 22;21(7):2759-65. Epub 2014 Dec 22.

Department of Chemistry, Indian Institute of Technology, Kanpur-208016 (India), Fax: (+91) 512-2597436.

The metal ions in a neutral Zn-MOF constructed from tritopic triacid H3 L with inherent concave features, rigid core, and peripheral flexibility are found to exist in two distinct SBUs, that is, 0D and 1D. This has allowed site-selective postsynthetic metal exchange (PSME) to be investigated and reactivities of the metal ions in two different environments in coordination polymers to be contrasted for the first time. Site-selective transmetalation of Zn ions in the discrete environment is shown to occur in a single crystal-to-single crystal (SCSC) fashion, with metal ions such as Fe(3+) , Ru(3+) , Cu(2+) , Co(2+) , etc., whereas those that are part of 1D SBU sustain structural integrity, leading to novel bimetallic MOFs, which are inaccessible by conventional approaches. To the best of our knowledge, site-selective postsynthetic exchange of an intraframework metal ion in a MOF that contains metal ions in discrete as well as polymeric SBUs is heretofore unprecedented.
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http://dx.doi.org/10.1002/chem.201406098DOI Listing
February 2015

Crystal engineering: lattice inclusion based on O-H···O hydrogen-bonded self-assembly and guest-induced structural mimicry.

J Org Chem 2012 Sep 4;77(18):7858-65. Epub 2012 Sep 4.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

Pyrene-tetraphenol TP2 constitutes a molecular system with inherent features for inclusion of two or more guest molecules that are complementary in terms of size and shape. Hydrogen-bonded self-assembly of TP2 in the solid state is shown to lead to voids within which the guest molecules are incorporated. A large aromatic expanse extant to the pyrene core in TP2 permits inclusion of two different types of guest species interchangeably. The robust association manifests in packing equivalence in all of the inclusion compounds of TP2 with the exception of the compound formed with pyridine and o-dichlorobenzene guests; in the latter, pyridine terminates the otherwise 3-dimensional hydrogen-bonded organization. The half-component of TP2, i.e., 4,6-bis(4-hydroxyphenyl)-m-xylene (BX), deduced by simple structural reduction, is shown to exhibit guest inclusion, but with considerably less guest accessible volume. The limited yet meaningful set of guests allows mimicry of the two expected patterns of molecular organization based on hydrogen bonding for both TP2 and BX in the solid state.
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http://dx.doi.org/10.1021/jo3010292DOI Listing
September 2012
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