Smita Majumder

An oxorhenium(V) Schiff-base complex: synthesis, structure, spectroscopic characterization, electrochemistry, and DFT calculations

Reaction of the Schiff base 2-[(2-hydroxyethylimino)methyl]phenol (H2L) with trans-ReOCl3(PPh3)2 in 1 : 1 M ratio in dichloromethane gives [ReOCl2(HL)(PPh3)] (1) in substantial yield. The compound has been characterized by C, H, and N microanalyses, IR, UV-Vis, 1H NMR, and ESI-MS spectra. The X-ray crystal structure of the title compound has been determined. The structure reveals that it is an octahedral cis-Cl, Cl oxorhenium(V) complex where the relative positions of the two chlorides are cis. 1 crystallizes in the monoclinic space group P21/n with a = 14.198(2), b = 10.970(1), c = 18.258(1) Å, β = 111.83(1)°, V = 2640.0(3) Å3, and Z = 4. Electrochemical studies in dichloromethane show Re(V) to Re(VI) oxidation at 1.51 V along with two successive reductions – Re(V) to Re(IV) and Re(IV) to Re(III) at −0.66 V and −1.03 V versus Ag/AgCl, respectively. Geometry optimization of 1 vis-à-vis its trans analog, trans-Cl, Cl complex 2, has been performed at the level of density functional theory; 2 is more stable than 1 by 2 kcal M−1.

A new phenylimidorhenium(V) compound containing the 2-[(2-hydroxyethylimino)methyl]phenol Schiff-base ligand: experimental and theoretical aspects

Reaction of equimolar trans-[Re(NPh)(PPh3)2Cl3] with H2L, a 1 : 1 Schiff-base condensate of salicylaldehyde and ethanolamine, in chloroform gives trans-[Re(NPh)(HL)(PPh3)Cl2] (1a) in good yield. 1a has been characterized by C, H, and N microanalyses, FTIR and UV–vis spectra. The X-ray crystal structure of 1a reveals that it is an octahedral trans-Cl,Cl phenylimidorhenium(V) complex. The rhenium center has an ‘N2OCl2P’ coordination sphere. 1a crystallizes in the monoclinic space group P21/c with a = 11.2391(5), b = 16.4848(7), c = 16.3761(8) Å, V = 3034.0(2) Å3 and Z = 4. The electrochemical aspects of 1a have been studied. Electrochemical studies of 1a in dichloromethane show a quasi-reversible Re(V) to Re(VI) oxidation at 1.128 V versus Ag/AgCl. This redox potential reasonably matches the calculated redox potential, 1.186 V versus Ag/AgCl. Geometry optimization of the trans-Cl,Cl 1a vis-à-vis its cis analog, cis-Cl,Cl 1b, have been performed at the level of density functional theory (DFT). It is revealed that 1a is more stable than 1b by 21.6 kcal per mole of energy in the gas phase.

A new trans-dioxorhenium(V) complex with 4-aminopyridine: synthesis, structure, electrochemical aspects, DFT, and TD-DFT calculations

The reaction of 1 : 4.4 M proportion of cis-[ReO2I(PPh3)2] and 4-aminopyridine (ampy) in acetone–water gives trans-[ReO2(ampy)4]I·2H2O (1a) in 85% yield. 1a has been characterized by C, H, and N microanalyses, FT-IR, UV–vis, 1H NMR spectroscopy, and molar conductivity. The X-ray crystal structure of 1a reveals an octahedral trans dioxorhenium(V) complex with a “N4O2” coordination for rhenium. 1a has an orthorhombic space group C2221 with a = 17.576(4), b = 19.370(4), c = 15.730(4) Å, V = 5355(2) Å3, and Z = 8. Geometry optimization of the trans-O,O complex, 1a and its cis-O,O analog, 1b performed at the level of density functional theory reveal that 1a is more stable than 1b by 25 kcal M–1 in the gas phase. The electronic spectrum of 1a was also analyzed at the level of time-dependent density functional theory. Excitation of 1a in methanol at 450 nm leads to a fluorescent emission at 505 nm with a quantum yield (Ф) of 0.04. Electrochemical studies of 1a in acetonitrile show a quasi-reversible Re(V) to Re(VI) oxidation at 0.618 V versus Ag/AgCl. This redox potential matches with the calculated redox potential of 0.621 V versus Ag/AgCl. Graphical Abstract

Copper(II) thiocyanate complexes of 2-(2-pyridinyl)-benzthiazole: synthesis, structure, redox behavior, thermal aspects, and DFT calculations

Reaction of 2-(2-pyridinyl)-benzthiazole (Pbt), KSCN, and copper(II)perchlorate hexahydrate in 1 : 2 : 1 molar proportion in dimethyl sulfoxide gives monomeric [Cu(Pbt)(SCN)2DMSO] (1a). In another run, identical proportions of the same reactants in methanol generates a symmetric thiocyanate bridged dimeric copper(II) compound, [Cu2(Pbt)2(SCN)2] (2a), in 72% yield. Both 1a and 2a have been characterized by C, H, and N microanalyses, copper estimation, FTIR, UV–vis spectra, and room temperature magnetic susceptibility measurements. The X-ray crystal structures of 1a and 2a have been determined. Electrochemical studies of 1a and 2a show Cu(II) to Cu(III) oxidation in solution. The thermal behaviors of 1a and 2a have been studied. Bond valence sum method of analysis was performed to assign the oxidation state for each copper center in 1a and 2a. Geometry optimization of 1a, 2a, and their linkage isomers has also been performed at the level of the density functional theory to show that 1a and 2a are the most stable congeners. These results corroborate our experimental findings.

A copper(II) complex of benzimidazole-based ligand: synthesis, structure, redox aspects and fluorescence properties

Abstract Employing 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole (bpb) as a monodentate ligand, a new greenish-blue copper(II) complex, [Cu(bpb)2(NO3)2] (1a), has been synthesized. 1a has been characterized analytically and spectroscopically. The X-ray crystal structure of 1a reveals that it adopts a cis disposition with respect to the ligands. The solid state structure of 1a is stabilized by intramolecular offset face-to-face π–π stacking. Non-covalent supramolecular edge-to-face C–H⋯π interactions with neighboring molecules give 1-D supramolecular chains that further lead to the formation of an assembled 3-D supramolecular metal-organic framework via hydrogen bonding interactions. 1a shows blue fluorescence most likely due to intramolecular offset face-to-face π–π stacking. At room temperature, 1a is one-electron paramagnetic. It shows a rhombic EPR spectrum with g1 = 2.12, g2 = 2.42, and g3 = 2.52 in the solid state at liquid nitrogen temperature. In cyclic voltammetry, 1a displays a one-electron oxidative Cu(II)/Cu(III) couple. Our DFT calculations, corroborate the observed experimental results of 1a.