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Featured researches published by Apurba Biswas.


Inorganic Chemistry | 2012

Synthesis, Crystal Structures, Magnetic Properties and Catecholase Activity of Double Phenoxido-Bridged Penta-Coordinated Dinuclear Nickel(II) Complexes Derived from Reduced Schiff-Base Ligands: Mechanistic Inference of Catecholase Activity

Apurba Biswas; Lakshmi Kanta Das; Michael G. B. Drew; Guillem Aromí; Patrick Gamez; Ashutosh Ghosh

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni(2)(L(1))(2)(NCS)(2)] (1), [Ni(2)(L(2))(2)(NCS)(2)] (2), and [Ni(2)(L(3))(2)(NCS)(2)] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL(1)), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL(2)), and 2-[1-(3-dimethylamino-propylamino)-ethyl]-phenol (HL(3)), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter τ = 0.47) and 3 (τ = 0.29), while it is almost perfect for 2 (τ = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm(3) K mol(-1), in the convention H = -2JS(1)S(2)). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes.


Inorganic Chemistry | 2013

Di-, tri-, and tetranuclear nickel(II) complexes with oximato bridges: magnetism and catecholase-like activity of two tetranuclear complexes possessing rhombic topology.

Lakshmi Kanta Das; Apurba Biswas; Jared S. Kinyon; N. S. Dalal; Haidong Zhou; Ashutosh Ghosh

Oxime-based tridentate Schiff base ligands 3-[2-(diethylamino)ethylimino]butan-2-one oxime (HL(1)) and 3-[3-(dimethylamino)propylimino]butan-2-one oxime (HL(2)) produced the dinuclear complex [Ni2L(1)2](ClO4)2 (1) and trinuclear complex [Ni3(HL(2))3(μ3-O)](ClO4)4·CH3CN (2), respectively, upon reaction with Ni(ClO4)2·6H2O. However, in a slightly alkaline medium, both of the ligands underwent hydrolysis and resulted in tetranuclear complexes [{Ni(deen)(H2O)}2(μ3-OH)2{Ni2(moda)4}](ClO4)2·2CH3CN (3) and [{Ni(dmpn)(CH3CN)2}2(μ3-OH)2{Ni2(moda)4}](ClO4)2·CH3CN (4), where deen = 2-(diethylamino)ethylamine, dmpn = 3-(dimethylamino)-1-propylamine, and modaH = diacetyl monoxime. All four complexes have been structurally characterized. Complex 1 is a centrosymmetric dimer where the square planar nickel(II) atoms are joined solely by the oximato bridges. In complex 2, three square planar nickel atoms form a triangular core through a central oxido (μ3-O) and peripheral oximato bridges. Tetranuclear complexes 3 and 4 consist of four distorted octahedral nickel(II) ions held together in a rhombic chair arrangement by two central μ3-OH and four peripheral oximato bridges. Magnetic susceptibility measurements indicated that dinuclear 1 and trinuclear 2 exhibited diamagnetic behavior, while tetranuclear complexes 3 and 4 were found to have dominant antiferromagnetic intramolecular coupling with concomitant ferromagnetic interactions. Despite its singlet ground state, both 3 and 4 serve as useful examples of Kahns model for competing spin interactions. High-frequency EPR studies were also attempted, but no signal was detected, likely due to the large energy gap between the ground and first excited state. Complexes 3 and 4 exhibited excellent catecholase-like activity in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone, whereas 1 and 2 did not show such catalytic activity. Kinetic data analyses of this oxidation reaction in acetonitrile revealed that the catalytic activity of 3 (kcat = 278.4 h(-1)) was slightly lower than that of 4 (kcat = 300.0 h(-1)). X-band EPR spectroscopy indicated that the reaction proceeded through the formation of iminoxyl-type radicals.


CrystEngComm | 2011

Two unusual mixed-valent trinuclear CuII2CuI complexes containing copper(I) tribromide dianion as bridging ligand: Identification of an unprecedented doubly hydrogen-bonded water dimer

Apurba Biswas; Rajat Saha; Ashutosh Ghosh

Two very rare mixed-valent CuII2CuI trinuclear complexes, [Cu2(Br–L1)2CuBr3]·2H2O (1) and [Cu2(L2)2CuBr3]·2CH3OH (2) have been synthesized using CuBr2 and the tridentate reduced Schiff-base ligands HL1 (2-[(2-dimethylamino-ethylamino)-methyl]-phenol) and HL2 (2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol), respectively. The complexes have been characterized by X-ray structural analyses. In both complexes, the deprotonated tridentate reduced Schiff base forms a di-μ-phenoxo bridge between the two CuII centers and the CuBr32− anion acts as an additional bridge between them to result in the trinuclear structures. During complex formation, ligand HL1 has been brominated at the five position of the aromatic ring but HL2 did not undergo any such reaction. In complex 1 an unprecedented doubly hydrogen-bonded water dimer, which is considered as an important transition state for the interchange of hydrogen atoms within the water dimer, has been identified. The dimensions of this water dimer agree quite well to those obtained from theoretical calculations.


CrystEngComm | 2012

Effect of a methyl group on the spontaneous resolution of a square-pyramidal coordination compound: crystal packing and conglomerate formation

Apurba Biswas; Carolina Estarellas; Antonio Frontera; Pablo Ballester; Michael G. B. Drew; Patrick Gamez; Ashutosh Ghosh

Reaction of [Cu(pic)2]·2H2O (where pic stands for 2-picolinato) with 2-({[2-(dimethylamino)ethyl]amino}methyl)phenol (HL1) produces the square-pyramidal complex [CuL1(pic)] (1), which crystallizes as a conglomerate (namely a mixture of optically pure crystals) in the Sohncke space group P212121. The use of the methylated ligand at the benzylic position, i.e. (±)-2-(1-{[2-(dimethylamino)ethyl]amino}ethyl)phenol (HL2), yields the analogous five-coordinate complex [CuL2(pic)] (2) that crystallizes as a true racemate (namely the crystals contain both enantiomers) in the centrosymmetric space group P21/c. Density functional theory (DFT) calculations indicate that the presence of the methyl group indeed leads to a distinct crystallization behaviour, not only by intramolecular steric effects, but also because its involvement in non-covalent C–H⋯π and hydrophobic intermolecular contacts appears to be an important factor contributing to the crystal-lattice (stabilizing) energy of 2.


Inorganic Chemistry | 2012

Insertion of a hydroxido bridge into a diphenoxido dinuclear copper(II) complex: drastic change of the magnetic property from strong antiferromagnetic to ferromagnetic and enhancement in the catecholase activity.

Apurba Biswas; Lakshmi Kanta Das; Michael G. B. Drew; Carmen Diaz; Ashutosh Ghosh


Inorganic Chemistry | 2010

Use of a reduced Schiff-Base ligand to prepare novel chloro-bridged chains of rare Cu(II) trinuclear complexes with mixed azido/oxo and chloro/oxo bridges.

Apurba Biswas; Michael G. B. Drew; Carlos J. Gómez-García; Ashutosh Ghosh


Polyhedron | 2010

Nickel(II) and copper(II) complexes of unsymmetrical tetradentate reduced Schiff base ligands

Apurba Biswas; Michael G. B. Drew; Ashutosh Ghosh


Polyhedron | 2013

Polymorphism in hetero-metallic tri-nuclear CuII2CdII complexes of salicylaldimine ligand: Structural analysis and theoretical study

Lakshmi Kanta Das; Apurba Biswas; Antonio Frontera; Ashutosh Ghosh


Dalton Transactions | 2012

Cis-trans isomerism in diphenoxido bridged dicopper complexes: role of crystallized water to stabilize the cis isomer, variation in magnetic properties and conversion of both into a trinuclear species.

Apurba Biswas; Michael G. B. Drew; Carmen Diaz; Antonio Bauzá; Antonio Frontera; Ashutosh Ghosh


Inorganic Chemistry | 2014

Isolation of two different Ni2Zn complexes with an unprecedented cocrystal formed by one of them and a "coordination positional isomer" of the other.

Lakshmi Kanta Das; Apurba Biswas; Carlos J. Gómez-García; Michael G. B. Drew; Ashutosh Ghosh

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Ashutosh Ghosh

College of Science and Technology

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Carmen Diaz

University of Barcelona

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Antonio Frontera

University of the Balearic Islands

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Joan Ribas

University of Barcelona

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Antonio Bauzá

University of the Balearic Islands

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