Preparation, structural and physical studies of mercury(II) halide complexes with the N,N′-chelating biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline

Abstract

The mercury(II) complexes [Hg 2X 4L 2] (X = Cl, Br) and [HgI 2L], 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 1H NMR spectroscopy. The structures of the free ligand L and [Hg 2Cl 4L 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) Å, β = 94.79(2)° and Z=4. The complex [Hg 2Cl 4L 2] crystallizes in space group P2 1/ n with a = 7.627(3), b = 15.617(4), c = 11.099(4),β=92.03(3)° 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 2Cl 4L 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 2Cl 4L 2], while a monomeric pseudotetrahedral structure is assigned for the iodo complex in the solid state.