AN UNEXPECTED STOICHIOMETRIC EFFECT IN BOTH SOLUTION AND SOLID-STATE IN MERCURY-RICH DITHIOCARBAMATE CATION CHEMISTRY - CRYSTAL AND MOLECULAR-STRUCTURE OF POLYMERIC TRIS(PIPERIDINECARBODITHIOATO)DIMERCURY(II) PERCHLORATE

An unusual stoichiometric effect has been observed both in solution and in the solid state for mercury-rich cations derived from Hg(RR'dtc)2 complexes (RR'dtc = dithiocarbamate) when the remote organic substituent is changed from two alkyl groups to one heterocyclic group. Polarographic and voltammetric studies have been carried out on dichloromethane (0.1 M Bu4NClO4) solutions of Hg(pipdtc)2 (pip = piperidyl) at mercury electrodes. The product formed during the first oxidation process is shown to be [Hg4(pipdtc)6]2+ or some multiple of this, and evaporation of the solution leads to the isolation of polymeric [Hg2(pipdtc)3]ClO4. These are stoichiometries different from those of the products ([Hg3(Et2dtc)4]2+ and [Hg5(Et2dtc)8]2+) obtained under similar conditions from Hg(Et2dtc)2, so that merely varying the substituent on the dithiocarbamate ligand has the dramatic and highly unusual effect of changing the stoichiometry of the resulting mercury complexes in both phases. Crystal data for [Hg2(pipdtc)3]ClO4: M(r) = 981.5, monoclinic space group P2(1)/c, a = 9.743 (2) angstrom, b = 12.289 (3) angstrom, c = 24.618 (4) angstrom, beta = 90.51 (2)-degrees, Z = 4, rho-measd = 2.21 g cm-3, Mo K-alpha radiation, R = 0.070, R(w) = 0.063 for 2264 independent reflections. The crystal structure is composed of two parallel polymeric chains in the [0, 1, 0] direction, and the repeating unit of each chain is a pair of asymmetric [Hg2(pipdtc)3]ClO4 units related by a center of symmetry at (1/2, 1/2, 0). The environments of the unique mercury atoms Hg1 and Hg2 are very similar, apart from the weak coordination of the perchlorate ion to Hg2. Both are coordinated to four sulfur atoms at distances ranging from 2.36 to 2.92 angstrom, resulting in a grossly distorted tetrahedral configuration for both Hg1 and Hg2. Two dithiocarbamates of one type are chelated to one mercury atom with one of the sulfur atoms also bridging to another mercury atom, while the other type of dithiocarbamate ligand bridges between two mercury atoms.