Department of Chemistry

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Author: search.filters.author.Sarkar, MadhushreeSubject: search.filters.subject.Crystal structures

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    Two pillared-layer metal–organic frameworks based on the pinwheel trinuclear carboxylate-clusters of Zn(II) and Co(II): synthesis, crystal structures, magnetic study, and Lewis acid catalysis
    (RSC, 2023) Sarkar, Madhushree
    Using a dicarboxylic acid, [1,1′-biphenyl]-4,4′-dicarboxylic acid (H2L1) and an exobidentate ligand, (1E,1′E)-N,N′-(1,4-phenylene)bis(1-(pyridin-4-yl)methanimine) (L2), two 3D interpenetrated networks, {[Zn3(L1)3(L2)]·9H2O}n (Zn-MOF) and {[Co3(L1)3(L2)(DMF)]·0.5DMF}n (Co-MOF), have been prepared in good yields. The crystal structure analysis of Zn-MOF and Co-MOF revealed that both have a 3D pillared-layer structure based on pinwheel trinuclear metal–carboxylate clusters as secondary building units (SBUs). Furthermore, the structures also exhibited three-fold interpenetration. Although the overall networks in Zn-MOF and Co-MOF showed significant resemblances, there are marked differences in their crystal structures, which are associated with the coordination environment of the metal centre and the binding modes of the carboxylates. Gas adsorption studies (N2 at 77 K and 1 bar) indicated that Co-MOF is more porous than Zn-MOF. Magnetic measurements on Co-MOF indicate a significant antiferromagnetic interaction (45 K to 303 K) between trimeric Co(II) S = 3/2 spins through syn–syn carboxylato bridges. Both MOFs were studied for the Lewis acid catalyzed Knoevenagel condensation reactions between benzaldehydes and malononitrile with an active methylene group, where Zn-MOF was found to be a better catalyst than Co-MOF. This was supported by the Monte Carlo simulations indicating the better substrate binding ability of Zn-MOF than Co-MOF.
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    Interplay of Hydrogen Bonds in Assembling (4,4)-Coordination Networks:  Transformations from Open to Interpenetrated Networks via Anion Exchange
    (ACS, 2006) Sarkar, Madhushree
    Open (4,4)-coordination networks were shown to assemble via N−H···O hydrogen bonds in two different ways:  the usual offset packing via β-sheet hydrogen bonds and an unprecedented trigonal packing. Both of the structures have continuous channels that are occupied by guest molecules (nitrobenzene or EtOH and H2O) which account for 37% or 28% of the crystal volume. Interestingly, these complexes have shown an ability to exchange ClO4- with PF6- ions and transform into the doubly interpenetrated varieties.