Zn(NCS)2-3-cyanopyridine Coordination Compounds: Synthesis, Crystal Structures, and Thermal Properties

The reaction of different stoichiometric amounts of Zn(NCS)(2) with 3-cyanopyridine in different solvents leads to the formation of several new coordination compounds, which were structurally characterized and investigated for their thermal behavior. In Zn(NCS)(2)(3-cyanopyridine)(4) (1) and Zn(NCS)(2)(3-cyanopyridine)(2)(H2O)(2)(3-cyanopyridine)(2) (2) the zinc cations are octahedrally coordinated by two terminally N-bonded thiocyanate anions and four 3-cyanopyridine (1) or two 3-cyanopyridine and two water molecules (2) within slightly distorted octahedra. Zn(NCS)(2)(3-cyanopyridine)(2) (3) and Zn(NCS)(2)(3-cyanopyridine)(2)(H2O)(0.5) (3-H2O) also form discrete complexes but with tetrahedrally coordinated Zn cations. Upon heating compound 1 decomposes without the formation of any intermediate compound. In contrast, compound 2 loses the water molecules in the first step and transforms into compound 1. Surprisingly, upon further heating a second TG step is observed, in which compound 3 is formed as an intermediate, which is not observed if compound 1 is heated directly. The tetrahedral complex 3 melts leading to the formation of an amorphous phase. If the hemihydrate 3-H2O is heated, it transforms into 3 via melting and crystallization but there are hints that a metastable phase might form as intermediate on water removal.