Synthesis, Crystal Structure, and Thermal and Magnetic Properties of New Transition Metal–Pyrazine Coordination Polymers

Abstract

AbstractThe reaction of nickel thiocyanate with pyrazine in a 1:2 ratio leads to the new ligand‐rich 1:2 (ratio metal/ligand) compound [Ni(SCN)2(pyrazine)2]n (1), in which the metal atoms are coordinated by four N atoms of pyrazine ligands and two N atoms of thiocyanate anions in a slightly distorted octahedral arrangement. If an excess of the metal thiocyanate is used and the reaction is performed under solvothermal conditions, single crystals of the ligand‐deficient 1:1 compounds [M(SCN)2(pyrazine)2]n [M = Fe (2I), Co (3), Ni (4)] are obtained. Compound 2I is isotypic with [Mn(SCN)2(pyrazine)]n but different to 3 and 4, which are also isotypic. Investigations on the synthesis of these compounds reveal that only compound 4 can be prepared phase‐pure in solution; all other ligand‐deficient compounds are always contaminated with large amounts of the corresponding ligand‐rich coordination polymers. In the crystal structures, the metal atoms are surrounded by two N atoms of the pyrazine ligands as well as by two N atoms and two S atoms of the thiocyanate anions in a slightly distorted octahedral geometry. In contrast to the ligand‐rich 1:2 coordination polymers, the metal atoms are further linked into layers by the thiocyanate anions due to μ2‐N,S coordination. On heating, compound 1 and the ligand‐rich 1:2 coordination polymers [M(SCN)2(pyrazine)2]n (M = Fe, Co) transform quantitatively into the ligand‐deficient compounds. Surprisingly, thermal decomposition of the iron compound leads to a new modification (2II), which is isotypic to compounds 3 and 4. The magnetic properties of all compounds have been investigated and are found to be dependent on the connection mode of the thiocyanate anions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)