Dimorphic Modification of the Trinuclear Nickel(II) Complex [Ni 3 (NCS) 6 (pdz) 6 ]: Synthesis, Crystal Structure, Thermal, Magnetic and Spectroscopic Properties

Reaction of nickel(II) thiocyanate and pyridazine (pdz) as organic spacer ligand leads to the formation of the ligand‐rich 1:2 (1:2 = metal to ligand ratio) trinuclear nickel(II) complex of composition [Ni 3 (NCS) 6 (pdz) 6 ]. Depending on the reaction solvent, different polymorphic modifications are obtained: Reaction in acetonitrile leads to the formation of the new modification 1I and reaction in ethanol leads to the formation of modification 1II reported recently. In their crystal structures discrete [Ni 3 (NCS) 6 (pdz) 6 ] units are found, in which each of the Ni 2+ cations exhibits a NiN 6 distorted octahedral arrangement. The central Ni 2+ cation is coordinated by four bridging pdz ligands and two thiocyanato anions in trans positions. Both thiocyanato anions exhibit the end‐on bridging mode. The peripheral Ni 2+ cations are bridged by one thiocyanato anion and by two pdz ligands with the central Ni 2+ cation. Further they are coordinated by two terminal N ‐bonded thiocyanato anions and one terminal N ‐bonded pdz ligand. The structure of 1I was determined by X‐ray single crystal structure investigation and emphasized by infrared spectroscopy. Magnetic measurements revealed a quasi Curie behavior with net ferromagnetic interactions for 1I and net antiferromagnetic interactions for 1II . Solvent‐mediated conversion experiments clearly show that modification 1I represents the thermodynamic most stable form at room temperature and that modification 1II is metastable. On thermal decomposition, both modification transform quantitatively in a new ligand‐deficient intermediate. Elemental analysis revealed a 3:4 compound of composition [Ni 3 (NCS) 6 (pdz) 4 ]. A structure model supported by IR spectroscopic investigations was assumed, in which three coordination modes of the thiocyanato anion exist, resulting in a 2D polymeric network.