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

Abstract

Two new nickel(II) bridging-cyanate complexes of formula [{Ni(323-tet)(µ-OCN)}_n][ClO₄]_n1[323-tet =N,N′-bis(3-aminopropyl)ethane-1,2-diamine] and [{Ni(Me₆[14]aneN₄)}₂(µ-OCN)₂][ClO₄]₂2(Me₆[14]aneN₄=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. Compounds 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-Hückel calculations and a generic superexchange model for the nickel(II) pseudohalogen system is proposed.