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The Crystal Structures of Bis(halo-mu-halo-(1, 3-thiazolidine-2-thione-S)mercury(II) (Halo=bromo, iodo) and Bis(1, 3-thiazolidine-2-thione-S)mercury(II) iodide

The sustained interest in the coordination chemistry of mercury(II) and methylmercurio salts has resulted from the inherent toxicity of these compounds. Such toxic behaviour derives from the affinity of mercury(II) atom for cysteinyl sulfur residues in a variety of biosystems. Heterocyclic thiones are among the ligand systems used to mimic biorelevant mercury-to-sulfur intreractions. In the structures of mercury(II) compounds with various heterocyclic thiones mostly the monodentate thione-sulfur donating character of the ligand was established.1-7 Mercury(II) halides or pseudohalides form 1:1 or 1:2 complexes with heterocyclic thiones depending upon the molar ratio of the reactants. The crystal structures of the 1:2 complexes usually consist of discrete monomeric molecules with tetrahedrally coordinated mercury atoms (more or less distorted). In contrast, the structural chemistry of the 1:1 complexes, which are often dimeric or polymeric, is difficult to systematize and generally depends on the type of halide ions used. As a part of our continuing research program we determined the structural features of HgX2(tzdtH) (X = Br (1), I (2) ; tzdtH = 1, 3-thiazolidine-2-thione) and HgI2(tzdtH)2 (3) (Scheme). The centrosymmetrical dimers of 1 and 2, formed by crystallographically imposed inversion centre, consist of two tetrahedra sharing the common edge, typical structural motif for binuclear halogeno-bridged mercury(II) complexes. The structures are similar, but not isostructural. Each Hg atom in 1 and 2 is coordinated by exocyclic thione S atom [Hg-S 2.435(4) and 2.510(3) &Aring ; ; , in 1 and 2, respectively], one terminal X atom [Hg-Br1(terminal) 2.514(2) &Aring ; ; and Hg-I1(terminal) 2.670(1) &Aring ; ; ] and two bridging halogeno atoms [Hg-Br2(bridging) 2.757(2) and 2.896(2) &Aring ; ; and Hg-I2(bridging) 2.790(1) and 3.059(2) &Aring ; ; ] (Fig.1). The Hg-S distances in both complexes are shorter than the sum of covalent radii for tetrahedral Hg and S (2.52 &Aring ; ; ). In 1 the Hg-Br(terminal) bond distance is shorter, while Hg-Br(bridging) distances are longer than the sum of covalent radii for tetrahedral Hg and Br atom (2.62 &Aring ; ; ). In 2 one Hg-I(bridging) bond distance is shorter and the other is longer than the sum of covalent radii for tetrahedral Hg and I atom (2.81 &Aring ; ; ). The tetrahedral distortion is more pronounced in bromo than in iodo derivative [S-Hg-X(terminal) is 138.19(9)o for X=Br and 123.49(10)o for X = I]. Discrete dimers are held together only by van der Waals forces. HgI2(tzdtH)2, 3 exists as mononuclear tetrahedral complex with long Hg-S [2.672(1) &Aring ; ; ] and short Hg-I distance [2.6877(7) &Aring ; ; ].

mercury(II) halides; thiazolidine-2-thione; crystal structures

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