Volume 39, Issue 3-4

New tin(II) complexes of general stoichiometry [Sn(L) 2 ] with bidentate ligand, derived from amino acids with isatin, 5-chloroisatin have been synthesized. It is characterized by elemental analyses, molar conductance measurements, and molecular weight determinations. Bonding of these complexes is discussed in terms of their UV-visible, infrared, and nuclear magnetic resonance ( 1 H, 13 C, and 119 Sn NMR) spectroscopic studies. The ligands act as bidentate towards metal ions, via the azomethine nitrogen and deprotonated oxygen of the respective ligands. The bond length, bond angles, highest occupied molecular orbital, lowest unoccupied molecular orbital, chemical hardness, global softness, and the lowest energy model structure of the complexes have been determined by density functional theory (DFT) calculations at B3LYP/LanL2DZ level. A few representative ligands and their tin complexes have been screened for their antibacterial activities and found to be active in this respect.

The quantum-chemical calculations based on density functional theory (DFT) have been performed on the diphenyltin(IV) derivative of glycyl-phenylalanine (H 2 L) at the B3LYP/6-31G(d,p)/LANL2DZ(Sn) level of theory without any symmetry constraint. The harmonic vibrational frequencies were computed at the same level of theory to find the true potential energy surface minima. The various geometrical and thermochemical parameters for the studied complex are obtained in the gas phase. The atomic charges at all the atoms were calculated using the Mulliken population analysis, the Hirshfeld population analysis, and the natural population analysis. The charge distribution within the studied complex is explained on the basis of molecular electrostatic potential maps, frontier molecular orbital analysis, and conceptual DFT-based reactivity (global and local) descriptors, using the finite difference approximation method. The nature of O-Sn, N-Sn, N→Sn, and C-Sn bonds is discussed in terms of the conceptual DFT-based reactivity descriptors. The structural analysis of the studied complex has been conducted in terms of the selected bond lengths and bond angles. The structural and the atomic charge analyses suggest a distorted trigonal bipyramidal arrangement consisting of negatively charged centers around the positively charged central Sn atom.

Three tricyclohexyltin salicylates, 3-X-5-Y-2-HOC 6 H 2 COOSn(C 6 H 11 - c ) 3 (where X, Y=H, H 1 ; H, NO 2 2 ; NO 2 , NO 2 3 ), have been synthesized and characterized by means of elemental analysis, IR, and 1 H NMR spectra. The crystal structures of compounds 1–3 are determined by X-ray single crystal diffraction. In these compounds, the carboxylate is monodentate, and the tin atom adopts distorted tetrahedral coordination geometry. In 2 and 3 , the neighboring molecules are connected into a one-dimensional supramolecular chain by the intermolecular Sn···O weak interactions between tin and oxygen of nitro group. Bioassay results have shown that the compounds have good in vitro antibacterial activity against Escherichia coli .

Metal contamination of soil is a serious environmental problem due to mining and use of synthetic products (e.g. pesticides, paints, batteries, and industrial wastes), which are serious threat to human life. The current research is aimed at the remediation of soil contaminated with lead (II) and chromium (VI) using indigenous fungal strains through the comparative study of bioleaching and chemical leaching methods. The removal efficiencies of Pb (II) and Cr (VI) in bioleaching were higher than chemical leaching, where 99% Cr (VI) and 36% Pb (II) were removed by Aspergillus flavus (F3) in bioleaching through the production of approximately 332 mg L -1 malic acid, 213 mg L -1 succinic acid, and 35 mg L -1 citric acid. The removal efficiencies in chemical leaching were 21.30% for Pb (II) and 1.92% for Cr (VI) by malic acid, 29.30% for Pb (II) and 72% for Cr (VI) by succinic acid, 22.21% for Pb (II) and 60.70% for Cr (VI) by citric acid, and 2.20% for Pb (II) and 2.47% for Cr (VI) by oxalic acid. The sequential extraction procedure for Pb (II) and Cr (VI) before and after bioleaching showed that Pb (II) and Cr (VI) mostly bound to stable fractions after bioleaching. Scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX) helped to identify the characteristic changes in the morphology and elemental composition of A. flavus (F3) biomass before and after bioleaching, whereas Fourier transform infrared spectroscopy (FTIR) showed that fungal biomass contain hydroxyl, carboxyl, fatty acids, and amine groups on its surface. The results implied that the fungal strain A. flavus (F3) can be used to remediate soils contaminated with Pb (II) and Cr (VI).

Two novel coordination compounds, [Sr(atzp) 2 (H 2 O) 2 ]·CH 3 OH ( 1 ) and [Sr(dtzpha)(H 2 O) 3 ]·4H 2 O ( 2 ) [Hatzp=5-aminotetrazole-1-propionic acid, H 2 dtzpha=1,3-di(tetrazol-5-yl)benzene-N2,N2′-diacetic acid)], have been generated by using 5-aminotetrazole-1-propionic acid and 1,3-di(tetrazol-5-yl)benzene-N2,N2′-diacetic acid to react with strontium salts, respectively. X-ray diffraction analysis reveals that carboxylic groups of two ligands show the same coordination mode (the μ 1,1,3 -COO coordination mode), compound 1 displays a 1D structure while compound 2 shows a 2D structure, which implies the influence of the number of the carboxylic acid groups. Luminescence properties of 1 and 2 were investigated at room temperature in the solid state.

Reaction of dimethyl N -cyanodithioiminocarbonate, NCNC(SCH 3 ) 2 ( L ), and SnPh 3 Cl led to the formation of [ClPh 3 SnNCNC(SCH 3 ) 2 ] ( 1 ) which crystallizes in the monoclinic space group C 2/c with Z =8, a =19.152(2) Å, b =12.8659 (16) Å, c =19.063(3) Å, β =108.608(3) and V =4451.6(10) Å 3 . The structure of 1 consists of a SnPh 3 moiety trans -coordinated in apical positions by one L ligand, N -coordinated, and one chlorine atom involving a trigonal bipyramid geometry around the Sn(IV) atom. To our knowledge, this is the first isolation of a discrete triorganotin(IV) complex with a N -cyanodithioiminocarbonate adduct. The structural characterization of 1 was completed by infrared and nuclear magnetic resonance spectroscopy, and elemental analysis which confirm the X-ray elucidation.

The reaction of bis(2-methyl-1 H -imidazol-3-ium) oxalate, [C 4 H 7 N 2 ] 2 [C 2 O 4 ], and bis(triphenyltin) oxalate, [(Ph 3 Sn) 2 (C 2 O 4 )], in methanol at room temperature yielded the formation of 2-methyl-1 H -imidazol-3-ium catena-O , O ′-oxalatotriphenylstannate, [C 4 H 7 N 2 ][Ph 3 Sn(C 2 O 4 )] ( 1 ), which crystallizes in the monoclinic space group P 2 1 / c with Z =8 , a =16.9334(14) Å, b =17.3251(14) Å, c =14.5114(10) Å, β =90.590(2)°, and V =4257.0(6) Å 3 . The oxalate ligand of 1 displays a bridging coordination mode and thus links two SnPh 3 moieties through an axial coordination leading to the propagation of infinite polymeric chains along the c axis. All Sn(IV) atoms exhibit a trigonal bipyramid geometry. The negative charge of [Ph 3 Sn(C 2 O 4 )] - moieties is compensated by the presence of surrounding noncoordinating 2-methyl-1 H -imidazol-3-ium cations. From a supramolecular point of view, the Sn-based chains are connected to one another through N-H···O hydrogen bond interactions involving oxalate ligands of distinct strands and doubly by the [C 4 H 7 N 2 ] + cations. The topology of the resulting crystal packing can be described as a two-dimensional layer network.

Reaction of potassium hydrotris(pyrazol-1-yl)borate ( KTp ) and n -BuSnCl 3 at room temperature led to the quantitative formation of TpSn(Cl) 2 ( n -Bu) ( 1 ). Colorless single crystals were obtained from a mixture of toluene/dichloromethane and were characterized as TpSn(Cl) 2 ( n -Bu)·½ toluene. Complex 1 crystallizes in the triclinic P 1̅ space group, with Z =2, a =8.0496(8) Å, b =9.4867(9) Å, c =14.2710(14) Å, α =90.365(3)°, β =104.479(3)°, γ =95.066(3)°, and V =1050.60(18) Å 3 . Its structure exhibits a piano stool conformation involving a distorted octahedral geometry around the central Sn(IV) atom. In the crystal and from a supramolecular point of view, 1 is organized in pairs according to a V-shaped arrangement implicating pyrazolyl rings and through weak intermolecular interactions ( π-π , C-H··· π , and C-H···Cl). The structural analysis of 1 was completed by infrared and solution NMR spectroscopy measurements as well as elemental analysis, which confirm the X-ray elucidation.