Lewis-base adducts of lead(<scp>II</scp>) compounds. Part 4. Novel isomeric dimers of lead(<scp>II</scp>) thiocyanate–1 10-phenanthroline(1/2). Crystal structure determinations

Abstract

The 1 : 2 adduct of lead(II) thiocyanate–1,10-phenanthroline has been shown to crystallise as two distinct polymorphs, monoclinic and triclinic. Single-crystal X-ray structure determinations show that in both forms the complexes exist as discrete dimers, all lead environments being seven-co-ordinate. The lead environment in all cases comprises a pair of bidentate phenanthroline ligands, unidentate N-thiocyanate, and a pair of bridging thiocyanate ligands, one with bridging sulphur and one bridging through the terminal atoms. In the monoclinic form C2/c, the dimer has crystallographically imposed two-fold symmetry with the N,S-bridging thiocyanate disordered about that axis; this ligand in the triclinic form is fully ordered, with ligand rearrangement about one of the lead atoms so that the dimer symmetry is more nearly inversion rather than two-fold.