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Six Ru(II) complexes with formula [Ru(terpy)(L)]X (L = tridentate N,N,S − donor thiosemicarbazone ligands, X = PF 6 − ) have been synthesized and characterized by using standard analytical and spectroscopic techniques. The X-ray crystal structures of the complexes [Ru(terpy)(L 2 )]PF 6 ( 2 ) and [Ru(terpy)(L 3 )]PF 6 ( 3 ) have been determined. It was found that during complexation the hydroxyimino functionality of the parent ligands is converted to imine, which participates in coordination through the N-atom. The complexes are found to undergo two quasi-reversible oxidations on the positive side of the potential window (0 to +0.8 V) and three successive quasi-reversible/irreversible reductions on the negative side of the potential window (0 to −2 V). The fluoride sensing properties of all the complexes have been studied in solution using absorption spectra and 1 H NMR studies, as well as by cyclic voltammetric (CV) measurements. From the absorption titration studies the association constants and detection limit values of fluoride by the complexes have been determined. The association constant values were found to be reasonably high (logK a > 5) for complexes 3 – 6 , and these values are one order of magnitude greater than those observed for the corresponding free thiosemicarbazones. Selective fluoride sensing by these complexes is also signaled by the development of vivid colors, visible with the naked eye. [ABSTRACT FROM AUTHOR]

By using η 3 -(SCH 2 CH 2 SCH 2 CH 2 S) (SSS), 2-thiocytosine (HL 1 ) and 5-amino-1,3,4-thiadiazole-2-thiol (HL 2 ) as S-donor ligands two ‘3 + 1’ mixed ligand red oxorhenium(V) complexes of the type [ReO(SSS)(HL 1 )]Cl ( 1 Cl) and [ReO(SSS)(L 2 )] ( 2 ) have been synthesized. Both 1 Cl and 2 have been characterized by C, H and N microanalyses, 1 H NMR, FT-IR, UV–Vis spectra and conductivity measurements. The X-ray crystal structures of both 1 Cl and 2 have been determined. Electrochemical studies of 1 Cl in acetonitrile show four successive one-electron redox couples; while 2 in DMSO displays only two one- electron redox steps. A computational and conceptual Density Functional Theory (DFT) studies have been performed on various (3 + 1) complexes of Re(V). The fully-optimized complexes, 1 Cl and 2, adopt geometries that satisfactorily corroborate the X-ray structures. Subsequently these optimized structures were employed to investigate systematically the relative stabilities of various Re(V) complexes with varying ligands having N, O and S donor atoms. The electronic properties of 1 Cl and 2 were delved into employing the hybrid STMP TD-DFT method and the results were found to be in good harmony with the experimental observations. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of equimolar proportion of trans-ReOCl3(PPh3)2 with HL, a 1:1 Schiff-base condensate of salicylaldehyde and allylamine, in chloroform gives rise to ReO(L)(PPh3)Cl2 1a in optimal yield. 1a has been characterized by C, H and N microanalyses, ESI-MS, FT-IR, UV–Vis spectra, molar conductivity measurements. The X-ray crystal structure of 1a reveals that it is an octahedral cis-Cl,Cl oxorhenium(V) complex. The rhenium center is in ‘NO2Cl2P’ coordination sphere. 1a crystallizes in the orthorhombic space group Pna21 with a =17.3541(11), b =10.2737(6), c =15.2113(10)Å, V =2712.0(3)Å3 and Z =4. The photophysical and electrochemical aspects of 1a have been studied. Electrochemical studies in dichloromethane show Re(V) to Re(VI) oxidation at 1.437V along with a reduction of Re(V) to Re(IV) at −0.705V versus Ag/AgCl. Excitation of 1a in chloroform at 460nm leads to a fluorescent emission at 525nm with a quantum yield (Ф) of 0.17. Geometry optimization of the cis-Cl,Cl complex 1a vis-à-vis its trans analogue, trans-Cl,Cl complex 1b, have been performed at the level of the density functional theory (DFT). It is revealed that 1b is more stable than 1a by 4kcal per mole of energy in gas phase. [Copyright &y& Elsevier]

Abstract: Starting from the proligands 1-methyl-3-picolylbenzimidazoliumhexaflurophosphate (1) and 1-benzyl-3-picolylbenzimidazoliumhexaflurophosphate (2) Ag(I)–NHC complexes, 1-methyl-3-picolylbenz-imidazolylidenesilver(I)hexaflurophosphate (3) and 1-benzyl-3-picolylbenzimidazolylidenesilver(I)hexaflurophosphate (4) have been synthesized. PO2F2 bridged Ag(I)-bimetallic system (5 and 6) developed from 3 and 4 after treatment of AgPF6 and water. 1-Methyl-3-picolyl-benzimidazolylidene-gold(I)hexaflurophosphate(7) and 1-benzyl-3-picolylbenzimidazolylidenegold(I)hexaflurophosphate (8) have been synthesized by Ag–carbene transmetallation method. Further reaction of AgPF6 with 7 and 8 build up the heterobimetallic Ag(I)–Au(I) systems (9 and 10); significantly, PO2F2 unit holds two heterobimetallic Ag(I)–Au(I) units together. Solid state structures of 3, 5, 8 and 9 have been determined by X-ray diffraction studies. Closed shell d10–d10 interactions are ascertained by the luminescence of bimetallic systems 7–10 upon irradiation of UV light. [Copyright &y& Elsevier]

Abstract: Experimental and theoretical studies of a new class of novel annulated imidazolium scffords 2a, 2b, 2c and their Hg(II)–NHC complexes 3a, 3b and 3c have been synthesized and characterized by different spectroscopic techniques. Molecular structures of 3a and 3b have been determined by single crystal X-ray diffraction studies. Virtual linear geometry [Ccarbene–Hg–Ccarbene 176.56(17)°] around Hg of the complex 3b is observed where as in 3a and 3c its deviate a more. DFT calculations provide geometrical parameters in conformity with the experimental values in case of 3a. The molecules prefer syn configuration over the anti due to lower energy supported by theoretical studies. Attention has given paid for theoretical calculations and comparison of 3a and 3c to observe the steric effect of –CH3 group in the scaffords where as in case of 3b the –CH3 group remain innocent. [Copyright &y& Elsevier]