The influence of the metal cation and the N-donor ligand on the reactivity and structures of Cd and Zn coordination compounds with 3-bromopyridine and 3-chloropyridine

Abstract

Reaction of cadmium thiocyanate and zinc thiocyanate with an excess of 3-bromopyridine and 3-chloropyridine leads to single crystals of four coordination compounds of composition M(NCS)2(3-bromopyridine)4 (M=Cd (Cd1-Br), Zn (Zn1-Br)) and M(NCS)2(3-chloropyridine)4 (M=Cd (Cd1-Cl), Zn (Zn1-Cl)). These compounds forms pairs of isotypic compounds (Cd1-Br and Zn1-Br in space group P-1 and Cd1-Cl and Zn1-Cl in space group C2/c) in which the metal cation are octahedral coordinated by two terminal thiocyanato anions and four neutral N-donor ligands into discrete complexes. If less N-donor ligands are used in the synthesis, compounds of composition M(NCS)2(3-bromopyridine)2 (M=Cd (Cd2-Br), Zn (Zn2-Br)) and M(NCS)2(3-chloropyridine)2 (M=Cd (Cd2-Cl), Zn (Zn2-Cl)) are obtained. In the crystal structure of the isotypic compounds Cd2-Br and Cd2-Cl (monoclinic space group P21/c) the metal cations are octahedral coordinated by two N-donor ligands and four thiocyanato anions and are linked into chains by the anionic ligands. In contrast, the Zn compounds Zn2-Br and Zn2-Cl are not isotypic but form similar discrete complexes in which the metal cations are tetrahedral coordinated by two terminal N-bonded thiocyanato anions and two neutral N-donor ligands. On heating compounds 1 half of the ligands are removed and a transformation into compounds 2 is observed. The structures and reactivity of these compounds are discussed and compared with those of related compounds.