Structure and magnetic behaviour of the first singly bridged nickel cyanate chain and a new dinuclear complex: An approximation to the superexchange mechanism for the nickel pseudohalide system

Two new nickel(II) bridging-cyanate complexes of formula [{Ni(323-tet)(mu-OCN}(n)][ClO4](n) 1 [323-tet = N,N'-bis(3-aminopropyl)ethane-1 ,2-diamine] and [{Ni(Me(6)[l4]aneN(4))}(2)(mu-OCN)(2)][ClO4](2) 2 (Me(6)[14]aneN(4) = DL-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized. The crystal structures of 1 and 2 have been solved and in both compounds the cyanate ligand acts as an end-to-end bridge with the nickel atoms in a NIN5O octahedral environment. Compound 1 is a chain In which the Ni(323-tet) fragments are linked by single cyanate bridges in a trans position, whereas compound 2 consists of dinuclear units with two cyanate bridges in a cis arrangement. Magnetic measurements In the 2-300 K range indicate weak ferromagnetism for 1 and antiferromagnetic behaviour for 2. Magneto-structural correlations have been obtained by Extended-Huckel calculations and a generic superexchange model for the nickel(II) pseudohalogen system is proposed.