Synthesis, Structures, and Thermal Properties of Cobalt(II) Thiocyanate Coordination Compounds with 2,5‐Dimethylpyrazine

Reactions of Co(NCS) 2 with 2,5‐dimethylpyrazine lead to the formation of five compounds of compositions Co(NCS) 2 (H 2 O) 4 · 4(2,5‐dimethylpyrazine) ( 1 ), Co(NCS) 2 (H 2 O) 4 · 3(2,5‐dimethylpyrazine) ( 2 ), Co(NCS) 2 (2,5‐dimethylpyrazine)(H 2 O) 2 · 3(2,5‐dimethylpyrazine) ( 3 ), [Co(NCS) 2 ] 2 (H 2 O) 6 · 4(2,5‐dimethylpyrazine) · 4H 2 O ( 4 ), and Co(NCS) 2 (2,5‐dimethylpyrazine)(MeOH) 2 ( 5 ). 1 and 2 are simple aqua complexes, in which the Co cations are octahedrally coordinated by two thiocyanate anions and four water molecules, whereas in 3 the Co cations are linked by the 2,5‐dimethylpyrazine ligands into chains. In compound 4 Co(NCS) 2 ](H 2 O) 6 dimers are observed, which are linked by bridging water molecules. In compound 5 the Co cations are connected into chains by the 2,5‐dimethylpyrazine co‐ligand and are additionally coordinated by terminal anionic ligands and methanol molecules. Thermogravimetric measurements of compounds 1 – 4 show several mass steps, in which the water and the co‐ligands and the water molecules are stepwise removed. Elemental analysis, XRPD investigations, and IR spectroscopic investigations indicate that all of these compounds decompose into new phases of composition Co(NCS) 2 (2,5‐dimethylpyrazine) 2 ( 6 ) that on further heating decompose into [Co(NCS) 2 ] 3 (2,5‐dimethylpyrazine) ( 8 ) via Co(NCS) 2 (2,5‐dimethylpyrazine) ( 7 ) as intermediate. Compound 7 can be directly obtained by thermal removal of methanol from compound 5 .