Synthesis, Crystal Structures and Polymorphism of New Cadmium and Zinc Thio- and Selenocyanato Coordination Compounds with 4-Acetylpyridine as N-Donor Ligand

Reactions of cadmium(II) thioand selenocyanate with 4-acetylpyridine in different molar ratios and in different solvents always lead to the formation of compounds of composition Cd(NCS)2(4acetylpyridine)2 (Cd1-I) and Cd(NCSe)2(4-acetylpyridine)2 (Cd2). Both compounds are isotypic and crystallize in the monoclinic space group C2/c. In their crystal structures the Cd cations are coordinated by two N-bonded 4-acetylpyridine ligands as well as two Nand two S/Se-bonded thioor selenocyanato anions within a slightly distorted octahedral geometry. The Cd cations are linked into chains by pairwise μ-1,3-coordinating thioor selenocyanato anions. In one reaction single crystals of a second polymorphic modification of composition Cd(NCS)2(4-acetylpyridine)2 (Cd1-II) were obtained by accident. This modification crystallizes monoclinically in space group P21/c, exhibits the same topology of the coordination network as in Cd1-I and Cd2 but a different arrangement of the chains in the crystal. Similar investigations with Zn(II) have revealed that only one compound of composition Zn(NCS)2(4-acetylpyridine)2 can be prepared that crystallizes in the triclinic space group P1̄. Its structure consists of discrete complexes in which the Zn(II) cations are tetrahedrally coordinated. A corresponding selenocyanato coordination compound could not be prepared.