PREPARATION, STRUCTURAL AND PHYSICAL STUDIES OF MERCURY(II) HALIDE-COMPLEXES WITH THE N,N'-CHELATING BIHETEROAROMATIC LIGAND 2-(2'-PYRIDYL)QUINOXALINE

The mercury(II) complexes [Hg(2)X(4)L(2)] (X=Cl,Br) and [HgI(2)L], where L is 2-(2'-pyridyl)quinoxaline, have been prepared and studied by; a combination of conductivity measurements and FT-IR and far-IR, Raman and H-1 NMR spectroscopy. The structures of the free ligand L and [Hg(2)Cl(4)L(2)] have been determined from three-dimensional X-ray data collected by counter methods. Compound L crystallizes in space group P2(1)/c with a=4.163(2), b=16.953(4), c=14.509(3) Angstrom, beta=94.79(2)degrees and Z=4. The complex [Hg(2)Cl(4)L(2)] crystallizes in space group P2(1)/n with a=7.627(3), b=15.617(4), c=11.099(4), beta=92.03(3)degrees and Z=2. In free L, the pyridine nitrogen and the nearest quinoxaline nitrogen are located on the opposite side of the carbon-carbon bond which connects the two rings; the reverse conformation has been observed on complexation. The structure of [Hg(2)Cl(4)L(2)] consists of two Hg(II) centres bridged by two chloro ligands, with a terminal chloride and a chelating molecule of L completing five-coordination at each metal. The geometry at mercury is a distorted trigonal bipyramid with the bridging chlorides occupying apical and equatorial sites of each Hg(II) atom. The bromo compound is isostructural with [Hg(2)Cl(4)L(2)], while a monomeric pseudotetrahedral structure is assigned for the iodo complex in the solid state.