Thiocyanato complexes of the coinage metals: synthesis and crystal structures of the polymeric pyridine complexes [AgxCuy(SCN)x + y(py)z]

From solutions of CuSCN or AgSCN in pyridine, several pyridine complexes of the thiocyanates with varying compositions and crystal structures were isolated depending on the reaction conditions. In CuSCN and in the orthorhombic modification of AgSCN the SCN– anions co-ordinate to four metal atoms as 1,1,1,3-µ4 bridges, whereas the degree of bridging decreases with increasing amounts of pyridine in the polymeric complexes [Cu(SCN)(py)z] and [Ag(SCN)(py)z] (z = 1 or 2). The distorted tetrahedral co-ordination of the metal atoms is preserved by co-ordination of pyridine ligands. Especially in the heteronuclear complexes [AgCu(SCN)2(py)4], [AgCu(SCN)2(py)3] and [Ag2Cu(SCN)3(py)3], interesting variants of structures result from the different possible modes of co-ordination of the SCN– ligand and from the preferred co-ordination of the “soft” S atoms to the “soft” Ag+ ions as defined by Pearson’s hard and soft acid and base principle.