• Tarlok S Lobana

      Articles written in Journal of Chemical Sciences

    • Stereochemical trends of metal derivatives of some heterocyclic-2-thiones and thiosemicarbazones

      Tarlok S Lobana

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      The interaction of heterocyclic thiones/thiosemicarbazones with metals has been the subject of several investigations as these ligands contain chemically active groups,-N(H)-C(=S)-↔ -N=C(-SH)-,and are useful model compounds for sulphur-containing analogues of purine and pyrimidine bases. Heterocylic-2-thiones bind to metals in several ways and lead to the formation of monomeric or polymeric complexes. For example, the simplest prototype of heterocylic-2-thiones, namely, pyridine-2-thione has several ways of binding, notably, terminal S-bonding and S-bridging (in neutral form), while in anionic form the modes are terminal S-bonding, S-bridging, N,S-chelation, N,S-bridging, N,S-chelation-cum-S-bridging and N,S-bridging-cum-S-bridging. Similarly, thiosemicarbazones bind to metals as S-bonded unidentates or N,S-chelates. In this paper, the chemistry of pyridine-2-thione, its N-oxide, 2-(benzylthio)pyridine-1-oxide thione with metals like iron(II), ruthenium(II), nickel(II), palladium(II), platinum(II), copper(I), copper(II), silver(I) and mercury(II) is briefly described. As regards thiosemicarbazones, focus is only on two compounds, namely organomercury(II) and organothallium(III). A variety of new molecules, well characterised by NMR and X-ray crystallography, is introduced.

    • Metal derivatives of heterocyclic-2-thiones: Variable donor ability, C-S rupture and new structural motifs

      Tarlok S Lobana Razia Sultana

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      The chemistry of thio-ligands based on heterocyclic-2-thiones, namely, pyridine-2-thione (SNC5H5), imidazolidine-2-thione (SN2C3H6), imidazoline-2-thione (SN2C3H4), 1-methyl-imidazoline-2-thione (SN2C4H6) and thiazolidine-2-thione (S2NC3H5) with coinage and some other metals are described. The synthesis, solvent effect, isolation of new products after C-S rupture and crystal structure are also discussed. For example, copper(I) bromide with 1-methyl-imidazoline-2-thione (SN2C4H6) in acetonitrile formed CuI trinuclear complex, {Cu3($\kappa^1$-Br)3(𝜇-SN2C4H6)3}·CH3CN. This reaction in the presence of chloroform involved C-S bond rupture, oxidation of sulphur to sulphate and bromination of ring and formed a tetranuclear cluster, Cu4($\kappa^1$-N-(N2C4H5Br)4($\mu_4$-O)(𝜇-Br)6] (N2C4H5Br = 2-bromo-1-methyl-imidazole). The reaction of copper(I) chloride with 1-methyl-imidazoline-2-thione (SN2C4H6) in acetonitrile also involved C-S rup ture and formed a chloro-bridged dinuclear complex [Cu2{$\kappa^2$-N,N-(N2C4H5)2S}2(𝜇-Cl)2Cl2] {(N2C4H5)2S = 1, 1'-dimethyl-2,2'-di-imidazolyl sulphide}. Significantly copper(I) bonded to more polarisable iodide ion (Cu-I) does not involve C-S rupture and in this case it formed CuI polynuclear complex, {Cu2(𝜇-I)2(𝜇-SN2C4H6)2}$_n$. Both copper(I) chloride and copper(I) bromide with 1-methyl-imidazoline-2-thione in dimethyl sulphoxide involved C-S rupture and oxidation of sulphur to sulphate and formed a sulphate chelated CuII complex, [CuII{$\kappa^2$-N,N-(N2C4H5)2S}($\eta^2$-O,OSO2)($\kappa^1$-OH2)]. Imidazolidine-2-thione (SN2C3H6) with copper(I) chloride/bromide in dimethyl sulphoxide gave a sulphate bridged polynuclear complex, [CuII{$\kappa^2$-N,N-(N2C3H5)2S}(𝜇-O,OSO2)($\kappa^1$-OH2)]$_n$ {(N2C3H5)2S = 2,2'-thio-di-2-imidazoline}. Other metals such as silver, zinc, cadmium and mercury formed monomers or dimers.

    • Reactivity of thiazolidine-2-thione towards CuI/CuII: Synthesis and structures of [3-(2-thiazolin-2-yl)thiazolidine-2-thione]copper(I) bromide and [bis(2,2′-bipyridine)nitratocopper(II)] nitrate

      Tarlok S Lobana Anu Rani Amanpreet K Jassal Jerry P Jasinski

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      Thiazolidine-2-thione (L1,NC3H5S2) reacted with copper(I) bromide in CH3CN under aerobic conditions and transformed through C-S bond cleavage into 3-(2-thiazolin-2-yl)thiazolidine-2-thione (L2, C3H4S2N-C3H4SN). This thio-ligand L2 with CuI ion yielded a three coordinate complex, [3-(2-Thiazolin-2-yl)thiazolidine-2-thione]copper(I)bromide 1a which crystallized in the triclinic system with the space group P1 as reported earlier. Treatment of 1a with bis(diphenylphosphino)methane (dppm) in dichloromethane also formed [3-(2-thiazolin-2-yl)thiazolidine-2-thione]copper(I) bromide 1b but it crystallized into the triclinic system with a new space group, P-1: 296(2) K, a, 7.3890(19); b, 8.473(2); c, 9.491(2) Å; 𝛼, 70.273(5); 𝛽, 67.170(5); 𝛾, 84.949(5)°; R, 6.79%. Reactions of copper(II) nitrate with thiazolidine-2-thione followed by the addition of 2,2′-bipyridine or with 2,2′-bipyridine first followed by the addition of thiazolidine-2-thione, gave blue crystals in both the cases. The x-ray crystallography revealed stoichiometry of the complex formed as: [Cu($\kappa^2$-N,N′-bipy)2($\kappa^1$-ONO2)](NO3) 2, which crystallized in monoclinic crystal system with space group, P21/n(14). Crystal data: 173(2) K, a, 11.318(1), b, 12.160(1), c, 14.967(1) Å; 𝛽 = 98.01(1)°, R, 3.99%; 296(2) K, a, 11.340(5), b, 12.249(5), c, 15.065(6) Å; 𝛽 = 98.04(2)◦, R, 4.09%.

    • Synthesis, molecular structures and ESI-mass studies of copper(I) complexes with ligands incorporating N, S and P donor atoms

      Tarlok S Lobana Arvinder Kaur Rohit Sharma Madhu Bala Amanpreet K Jassal Courtney E Duff Jerry P Jasinski

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      Equimolar reaction of copper(I) bromide with 2-thiouracil (tucH2) in acetonitrile-methanol formed a light yellow solid which on subsequent treatment with a mole of triphenyl phosphine (PPh3) in chloroform has yielded a sulfur-bridged dinuclear complex, [Cu2Br2 (𝜇-S-tucH2)2 (PPh3)2]·2CHCl3 1. A reaction of copper(I) bromide with two moles of 2,4-dithiouracil (dtucH2) in acetonitrile-methanol followed by addition of two moles of PPh 3 , designed to form [Cu(𝜇-S,S-dtuc)2 (PPh3)4 Cu] 2a, instead resulted in the formation of previously reported polymer, {CuBr(𝜇-S,S-dtucH2)(PPh3)}n 2. Reaction of copper(I) iodide with 2- thiouracil (tucH2) and PPh3 in 1:1:2 molar ratio (Cu:H2 tuc:PPh3) as well as that of copper(I) thiocyanate with pyridine-2-thione (pySH) or pyrimidine-2-thione (pymSH) and PPh3 in similar ratio, yielded an iodo-bridged unsymmetrical dimer, [(PPh3)2 (𝜇-I)2 Cu(PPh3)] 3 and thiocyanate bridged symmetrical dimer, [(PPh3)2 Cu(𝜇- N,S- SCN)2 Cu(PPh3)2] 4, respectively. In both the latter reactions, thio-ligands which initially bind to Cu metal center, are de-ligated by PPh3 ligand. Crystal data: 1, P21/c: 173(2) K, monoclinic, a, 13.4900(6); b, 17.1639(5); c, 12.1860(5) Å; 𝛽, 111.807(5)° ; R, 5.10%; 2, Pbca: 296(2) K, orthorhombic, a, 10.859(3); b, 17.718(4); c, 23.713(6) Å; 𝛼 = 𝛽 = 𝛾 , 90° ; R, 4.60%; 3, P2 1 : 173(2) K, monoclinic, a, 10.4208(7); b, 20.6402(12); c, 11.7260(7) Å; 𝛽, 105.601(7)° ; R, 3.97%; 4, P-1: 173(2) K, triclinic, a, 10.2035(4); b, 13.0192(5); c, 13.3586(6) Å; 𝛼, 114.856(4); 𝛽, 92.872(4)° ; 𝛾 , 100.720(4) ° ; R, 3.71%. ESI-mass studies reveal different fragments of complexes.

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