Department of Chemistry

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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.
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    Synthesis and Crystal Structure of 5, 5-diphenyldihydrofuran-2(3H)-one (5)
    (IOSR-JAC, 2016-03) Kumar, Indresh
    5,5-diphenyldihydrofuran-2(3H)-one(5) [C16H14O2] crystallizes in the monoclinic space group P21/c with the following unit cell parameters: a=8.132(5), b=13.224(5), c=11.785(5) Å, β=101.445(5)° and Z=4. The crystal structure was solved by direct methods and refined by full matrix least-squares procedure to a final R value of 0.054 for 1651 observed reflections. Furan ring adopts envelope conformation. Two phenyl rings are almost perpendicular to each other [dihedral angle = 85.66(7)°]. Crystal packing is stabilized by C-H…O intra molecular and weak C-H…π interactions.
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    Cis–trans isomerism in nickel(II)–diamine nitrite: synthesis and single crystal structure of an unusual cis-dinitronickel(II) complex, [NiL2(NO2)2] (L=1,2-diamino-2-methylpropane)
    (Elsiever, 2000-04-30) Laskar, Inamur Rahaman
    The complexes [NiL3](NO2)2·2H2O (violet, 1) and cis-[NiL2(NO2)2]·0.5H2O (pink, 1b) (L=1,2-diamino-2-methylpropane) have been synthesized from solution. The X-ray single crystal structure analysis of compound 1b has been carried out, but the presence of a water molecule cannot be detected. Upon heating, complex 1b undergoes dehydration followed by an endothermic phase transition to produce trans-[NiL2(NO2)2] (1d). The violet species (1) also undergoes dehydration upon heating with deamination resulting (1d).
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    Synthesis and characterization of cis and trans isomers of [NiL2(NCS)2] [L=1-(2-aminoethyl)pyrrolidine]: X-ray single-crystal structures
    (Elsiever, 2000-07-30) Laskar, Inamur Rahaman
    The isomeric complexes trans-[NiL2(NCS)2] (violet) (1) and cis-[NiL2(NCS)2] (blue) (2) [L=1-(2-aminoethyl)pyrrolidine] have been synthesized, varying solvents and temperature, and their X-ray crystal structures have been determined. Both the isomers possess the same space group, P21/c, having distorted octahedral geometry.
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    A 1D thiocyanato bridge nickel(II) system: crystal structure and magnetic property
    (Elsiever, 2001-04) Laskar, Inamur Rahaman
    A one-dimensional coordination polymer of nickel(II), [(μN,S-NCS)2{Ni(ampy)}]n (ampy=1-(2-aminoethyl)pyrrolidine) has been synthesized and characterized by X-ray single crystal analysis. Structure analysis reveals that each nickel(II) center is coordinated in a distorted octahedral fashion with four bridging thiocyanato ligands and one mesocyclic diamine ligand. The low temperature (300–18 K) magnetic measurement shows that the system is ferromagnetically coupled. The magnetic data are fitted to the de Neef equation, giving the parameters J=1.4 cm−1 and g=2.08.
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    Syntheses, characterisation and solid state thermal studies of 1-(2-aminoethyl)piperidine (L), 1-(2-aminoethyl)pyrrolidine (L′) and 4-(2-aminoethyl)morpholine (L″) complexes of nickel(II): X-ray single crystal structure analyses of trans-[NiL2(CH3CN)2](ClO4)2, trans-[NiL2(NCS)2] and trans-[NiL″2(NCS)2]
    (Elsiever, 2001-06-30) Laskar, Inamur Rahaman
    Reactions of nickel(II) salts with substituted ethane-1,2-diamine where one of the amine nitrogens is a part of a flexible cyclic ring, e.g. 1-(2-aminoethyl)piperidine (L), 1-(2-aminoethyl)pyrrolidine (L′) and 4-(2-aminoethyl)morpholine (L″) produce a number of complexes of the type: (i) Ni(AA)2X2 (where X=CF3CO2 −, SCN− and NO2 −; AA represents L/L′/L″); (ii) Ni(AA)2(CH3CN)2X2 (X=ClO4 − and NO3 −); (iii) Ni(AA)2(H2O)2X2 (X=CF3SO3 −, Cl−, Br− and I−); and (iv) Ni(AA)2(H2O)4X2 (X=0.5SO4 2−, 0.5SeO4 2− and CF3SO3 −). The complexes possess octahedral geometry. The major complexes upon desolvation retain trans-geometry, some of which are cis with respect to the counter-anion and a few of them are square planar. X-ray single crystal structure analyses of trans-[NiL2(CH3CN)2](ClO4)2, trans-[NiL2(NCS)2] (violet) and trans-[NiL″2(NCS)2] (sky-blue) have been done. The violet and sky-blue thiocyanato species have blue and green coloured isomers, respectively, and these pairs of isomers are proposed to be conformational isomers. Solid state thermal investigation of the complexes has been carried out. The complexes show thermochromism due to deaquation–anation/deaquation reaction/change of conformation. Only [NiL2](ClO4)2, [NiL′2(CF3CO2)2] and [NiL″2(NO2)2] undergo thermally induced phase transition. The effect of flexible ring size on diamine has been discussed.
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    Flexibility in co-ordinative behaviour of N-(3-hydroxypropyl)ethane-1,2-diamine toward cadmium(ii) halides: syntheses, crystal structures and solid state thermal studies
    (RSC, 2002) Laskar, Inamur Rahaman
    One new two-dimensional and two one-dimensional organic/inorganic composite coordination polymers have been synthesised by the reaction of cadmium(II) halides with N-(3-hydroxypropyl)ethane-1,2-diamine (L) and structurally characterised. [Cd(L)Cl2]n (1) is a two-dimensional sheet which is built from intersecting zigzag chains and forms a honeycomb like (6,3) net where each octahedral cadmium is linked with two bridging chloride atoms, one pendant chloride atom, two chelated nitrogen atoms of L and an oxygen atom from a neighbouring ligand; each cadmium(II) acts as a branching centre. [Cd(L)Br2]n (2) is a bromo bridged one-dimensional chain in which the non-chelated part of ligand L binds a neighbouring cadmium(II) centre resulting in an alternating array of four- and twelve-membered rings. [Cd(L)I2]n (3) is an iodo bridged one-dimensional network of alternating octahedral (CdN4I2) and tetrahedral cadmium(II) (CdI4) centres. Upon heating the complexes exhibit an irreversible endothermic phase transition [95–133 °C, ΔH = 29.5 kJ mol−1 for (1); 83–128 °C, ΔH = 22.5 kJ mol−1 for (2) and 91–128 °C, ΔH = 15.5 kJ mol−1 for (3)] yielding transparent films of CdLCl2 (1a), CdLBr2 (1b) and CdLI2 (1c) respectively. The derived species (1a, 1b and 1c) do not revert on keeping them in a humid atmosphere (relative humidity ≈ 60%) for several days but exhibit a glass transition upon heating.