Main Group Metal Halide Complexes with Sterically Hindered Thioureas XIII. Crystallographic Study of a Unique Cross-Linked Polymeric Dichlorolead(II) Complex with 1,1′-methylenebis(3-methyl-2(3H)-imidazolethione)
Chemistry and Biochemistry
Two complexes, PbCl2mbit and Pb(NCS) 2mbit (mbit = 1,1'-methylenebis(3-methyl-2)3H)-imidazolethione)) have been synthesized and characterized. A single crystal X-ray study of PbCl2mbit revealed a unique cross-linked polymeric structure composed of very distorted PbCl4S2 octahedra sharing common edges through long Pb-Cl bridges. The bridging pairs of Cl atoms are displaced cis to each other in the coordination sphere of lead thus creating twisted polymeric Pb-Cl strands running along the c axis. In the direction of the b axis, the strands are further linked by mbit ligands acting as bridges between neighboring twisted strands created by the lead chloride bonds. This is the first instance where mbit is shown to act a bridging ligand. There is no clear evidence for the lone pair of electrons through systematic distortions in the lead coordination sphere. A high m.p. of 259-261 °C is consistent with the polymeric structure. Cell parameters are as follows for PbCl2mbit: space group Pbca, a = 8.699(3), b = 17.164(4), c = 20.469(6) Å, Z = 8, V = 3056.2 Å3, Dc = 2.254 g /cm3, Do = 2.23g /cm3 (λ = 0.71073 Å). R = 0.047. Pb(NCS)2mbit complex was also synthesized and characterized, but crystals suitable for X-ray study were not obtained. IR stretching frequencies of the SCN group fall in the ranges obsd. for this ligand bonding only through N and no evidence for S bonding. The relatively high m.p. (254-256 °C) gives evidence for a polymeric structure the details of which remain unknown.