Abstract
Two complexes, PbCl 2mbit and Pb(NCS) 2mbit (mbit=1,1′-methylenebis(3-methyl-2)3 H)-imidazolethione)) have been synthesized and characterized. A single crystal X-ray study of PbCl 2mbit revealed a unique cross-linked polymeric structure composed of very distorted PbCl 4S 2 octahedra sharing common edges through long PbCl bridges. The bridging pairs of Cl atoms are displaced cis to each other in the coordination sphere of lead thus creating twisted polymeric PbCI 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 melting point of 259–261 °C is consistent with the polymeric structure. Cell parameters are as follows for PbCl 2mbit: space group Pbca, a=8.699(3), b=17.164(4), c=20.469(6) Å, Z=8, V=3056.2 Å 3, D c=2.254 g/cm 3, D o=2.23 g/cm 3 (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 observed for this ligand bonding only through N and no evidence for S bonding. The relatively high melting point (254–256 °C) gives evidence for a polymeric structure the details of which remain unknown.
Published Version
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