Chaitali Biswas

Bio: Chaitali Biswas is an academic researcher from University of Calcutta. The author has contributed to research in topics: Schiff base & Crystal structure. The author has an hindex of 11, co-authored 13 publications receiving 615 citations. Previous affiliations of Chaitali Biswas include Sarojini Naidu College for Women & University of Reading.

A Unique Example of Structural and Magnetic Diversity in Four Interconvertible Copper(II)―Azide Complexes with the Same Schiff Base Ligand: A Monomer, a Dimer, a Chain, and a Layer

Abstract: Four new Cu(II)-azido complexes of formula [CuL(N(3))] (1), [CuL(N(3))](2) (2), [Cu(7)L(2)(N(3))(12)](n) (3), and [Cu(2)L(dmen)(N(3))(3)](n) (4) (dmen = N,N-dimethylethylenediamine) have been synthesized using the same tridentate Schiff base ligand HL (2-[1-(2-dimethylaminoethylimino)ethyl]phenol, the condensation product of dmen and 2-hydroxyacetophenone). The four compounds have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 1 is mononuclear, whereas 2 is a single mu-1,1 azido-bridged dinuclear compound. The polymeric compound 3 possesses a 2D structure in which the Cu(II) ions are linked by phenoxo oxygen atoms and two different azide bridges (mu-1,1 and mu-1,1,3). The structure of complex 4 is a double helix in which two mu-1,3-azido-bridged alternating one-dimensional helical chains of CuL(N(3)) and Cu(dmen)(N(3))(2) are joined together by weak mu-1,1 azido bridges and H-bonds. The complexes interconvert in solution and can be obtained in pure form by carefully controlling the conditions. The magnetic properties of compounds 1 and 2 show the presence of very weak antiferromagnetic exchange interactions mediated by a ligand pi overlap (J = -1.77) and by an asymmetric 1,1-N(3) bridge (J = -1.97 cm(-1)), respectively. Compound 3 presents, from the magnetic point of view, a decorated chain structure with both ferro- and antiferromagnetic interactions. Compound 4 is an alternating helicoidal chain with two weak antiferromagnetic exchange interactions (J = -1.35 and -2.64 cm(-1)).

Anion-directed synthesis of metal-organic frameworks based on 2-picolinate Cu(II) complexes: A ferromagnetic alternating chain and two unprecedented ferromagnetic fish backbone chains

Abstract: Three new polynuclear copper(II) complexes of 2-picolinic acid (Hpic), {[Cu-2(pic)(3)(H2O)]ClO4}(n) (1), {[Cu-2(pic)(3)(H2O)]BF4}(n) (2), and [Cu-2(pic)3(H2O)(2)(NO3)](n) (3), have been synthesized by reaction of the "metalloligand" [Cu-(pic)(2)] with the corresponding copper(II) salts. The compounds are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Compounds 1 and 2 are isomorphous and crystallize in the triclinic system with space group P (1) over bar, while 3 crystallizes in the monoclinic system with space group P2(1)/n. The structural analyses reveal that complexes 1 and 2 are constructed by "fish backbone" chains through syn-anti (equatorial-equatorial) carboxylate bridges, which are linked to one another by syn-anti (equatorial-axial) carboxylate bridges, giving rise to a rectangular grid-like two-dimensional net. Complex 3 is formed by alternating chains of syn-anti carboxylate-bridged copper(II) atoms, which are linked together by strong H bonds involving coordinated nitrate ions and water molecules and uncoordinated oxygen atoms from carboxylate groups. The different coordination ability of the anions along with their involvement in the H-bonding network seems to be responsible for the difference in the final polymeric structures. Variable-temperature (2-300 K) magnetic susceptibility measurement shows the presence of weak ferromagnetic coupling for all three complexes that have been fitted with a fish backbone model developed for 1 and 2 (J = 1.74 and 0.99 cm(-1); J' = 0.19 and 0.25 cm(-1), respectively) and an alternating chain model for 3 (J = 1.19 cm(-1) and J' = 1.19 cm(-1)).

Anion–π, Lone-Pair–π, π–π and Hydrogen-Bonding Interactions in a CuII Complex of 2-Picolinate and Protonated 4,4′-Bipyridine: Crystal Structure and Theoretical Studies

Abstract: A Cu-II complex of protonated 4,4'-bipyridine (Hbyp) and 2-picolinate (pic), [Cu-2(pic)(3)(Hbyp)(H2O)(ClO4)(2)], has been synthesised and characterised by single-crystal X-ray analysis. The structure consists of two copper atoms that have different environments, bridged by a carboxylate group. The equatorial plane is formed by the two bidentate picolinate groups in one Cu-II, and one picolinate, one monodentate 4,4'-bipyridyl ligand and a water molecule in the other. Each copper atom is also weakly bonded to a perchlorate anion in an axial position. One of the coordinated perchlorate groups displays anion-pi interaction with the coordinated pyridine ring. The noncoordinated carboxylate oxygen is involved in lone-pair (l.p.)-pi interaction with the protonated pyridine ring. In addition there are pi-pi and H-bonding interactions in the structure. Bader's theory of "atoms in molecules" (AIM) is used to characterise the anion-pi and l.p.-pi interactions observed in the solid state. A high-level ab initio study (RI-MP2/aug-cc-pVTZ level of theory) has been performed to analyse the anion-pi binding affinity of the pyridine ring when it is coordinated to a transition metal and also when the other pyridine ring of the 4,4'-bipyridine moiety is protonated. Theoretical investigations support the experimental findings of an intricate network of intermolecular interactions, which is characterised in the studied complex, and also indicate that protonation as well as coordination to the transition metal have important roles in influencing the pi-binding properties of the aromatic ring. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis, crystal structure and magnetic properties of three unprecedented tri-nuclear and one very rare tetra-nuclear copper(II) Schiff-base complexes supported by mixed azido/phenoxo/nitrato or acetato bridges

Abstract: Three novel mixed bridged trinuclear and one tetranuclear copper(II) complexes of tridentate NNO donor Schiff base ligands [Cu3(L1)2(μ1,1-N3)2(CH3OH)2(BF4)2] (1), [Cu3(L1)2(μ1,1-N3)2(μ-NO3-1κO:2κO′)2] (2), [Cu3(L2)2(μ1,1-N3)2(μ-NO3-1κO:2κO′)2] (3) and [Cu4(L3)2(μ1,1-N3)4(μ-CH3COO-1κO:2κO′)2] (4) have been synthesized by reaction of the respective tridentate ligands (L1 = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, L2 = 2-[1-(2-diethylamino-ethylimino)-ethyl]-phenol, L3 = 2-[1-(2-dimethylamino-ethylimino)-methyl]-phenol) with the corresponding copper(II) salts in the presence of NaN3. The complexes are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Complex 1 is composed of two terminal [Cu(L1)(μ1,1-N3)] units connected by a central [Cu(BF4)2] unit through nitrogen atoms of end-on azido ligands and a phenoxo oxygen atom of the tridentate ligand. The structures of 2 and 3 are very similar; the only difference is that the central unit is [Cu(NO3)2] and the nitrate group forms an additional μ-NO3-1κO:2κO′ bridge between the terminal and central copper atoms. In complex 4, the central unit is a di-μ1,1-N3 bridged dicopper entity, [Cu2(μ1,1-N3)2(CH3COO)2] that connects two terminal [Cu(L3)(μ1,1-N3)] units through end-on azido, phenoxo oxygen and μ-CH3COO-1κO:2κO′ triple bridges to result in a tetranuclear unit. Analyses of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the copper(II) ions in complexes 1–3, with the exchange parameter J of −9.86, −11.6 and −19.98 cm−1 for 1–3, respectively. In complex 4 theoretical calculations show the presence of an antiferromagnetic coupling in the triple bridging ligands (acetato, phenoxo and azido) while the interaction through the double end-on azido bridging ligand is strongly ferromagnetic.

Aromatic rings in chemical and biological recognition: energetics and structures.

Abstract: This review describes a multidimensional treatment of molecular recognition phenomena involving aromatic rings in chemical and biological systems. It summarizes new results reported since the appearance of an earlier review in 2003 in host-guest chemistry, biological affinity assays and biostructural analysis, data base mining in the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB), and advanced computational studies. Topics addressed are arene-arene, perfluoroarene-arene, S⋅⋅⋅aromatic, cation-π, and anion-π interactions, as well as hydrogen bonding to π systems. The generated knowledge benefits, in particular, structure-based hit-to-lead development and lead optimization both in the pharmaceutical and in the crop protection industry. It equally facilitates the development of new advanced materials and supramolecular systems, and should inspire further utilization of interactions with aromatic rings to control the stereochemical outcome of synthetic transformations.

Jahn–Teller distortions in transition metal compounds, and their importance in functional molecular and inorganic materials

Abstract: This tutorial review discusses the structural and electronic consequences of the Jahn-Teller effect in transition metal complexes, focussing on copper(ii) compounds which tend to be the most studied. The nature of a Jahn-Teller distortion in molecular complexes and extended lattices can be manipulated by application of pressure or temperature, by doping a molecule into a host lattice, or simply by molecular design. Many of these results have been achieved using compounds with a trans-[CuX(4)Y(2)] coordination sphere, which seems to afford copper centres that are particularly sensitive to their environment. Jahn-Teller distortions lead to some unusual phenomena in molecular magnetism, and are important to the functionality of important classes of conducting and superconducting ceramics.

Supramolecular Self-Assembly of M-IDA Complexes Involving Lone-Pair···π Interactions: Crystal Structures, Hirshfeld Surface Analysis, and DFT Calculations [H2IDA = iminodiacetic acid, M = Cu(II), Ni(II)]

Abstract: Mononuclear copper(II) and nickel(II) complexes, [(C5H6N2)Cu(IDA)(H2O)] (1) and (C5H7N2)2[Ni(IDA)2(H2O)] (2) [H2IDA = iminodiacetic acid; C5H6N2 = 4-aminopyridine; C5H7N2 = protonated 2-aminopyridine], have been synthesized, and their crystal structures were solved using single crystal X-ray diffraction data. A detailed analysis of Hirshfeld surfaces and fingerprint plots facilitates a comparison of intermolecular interactions, which are crucial in building different supramolecular architectures. Molecules are linked by a combination of N–H···O, O–H···O and C–H···O hydrogen bonds into two-dimensional framework, whose formation is readily analyzed in terms of substructures of lower dimensionality with zero finite zero-dimensional dimeric units as the building blocks within the structures. Moreover, the aromatic molecules that are engaged in lone pair···π interactions with the noncoordinated carbonyl moieties play a crucial role in stabilizing the self-assembly process observed for both complexes. Intricate...