Synthesis, structures and magnetic properties of new Fe(II) and Co(II) thiocyanato coordination compounds with 2-chloropyrazine as Co-ligand

Investigations on the synthesis of coordination compounds based on Fe(NCS)2 and Co(NCS)2 with 2-chloropyrazine as ligand leads to the formation of five new compounds. Fe(NCS)2(2-chloropyrazine)4 (1-Fe), Co(NCS)2(2-chloropyrazine)4 (1-Co) and Fe(NCS)2(2-chloropyrazine)4·2-chloropyrazine solvate (2-Fe) consists of discrete complexes in which the metal cations are octahedrally coordinated and in which the thiocyanato anions are only terminal coordinated. On heating 1-Fe and 1-Co transform into new coordination polymers of composition [Fe(NCS)2(2-chloropyrazine)2]n (3-Fe) and [Co(NCS)2(2-chloropyrazine)2]n (3-Co) which are isotypic. No access to large and phase pure amounts of these compounds was found in solution but the structure of 3-Co was determined from a crystal obtained in one batch by accident. In the crystal structure of 3-Co and 3-Fe the metal(II) cations are coordinated by two N-bonded as well as two S-bonded thiocyanato anions and two 2-chloropyrazine ligands and are linked by μ-1,3-bridging anions into layers. Magnetic measurements of 1-Fe and 1-Co show only Curie- or Curie–Weiss paramagnetism, whereas for 3-Fe antiferromagnetic ordering and for 3-Co metamagnetic behavior is observed.