Linear hexanuclear nickel complexes with rich electrochemical features and facility to reduction

Two novel linear hexanuclear nickel complexes [Ni6(μ6-dpznda)4Cl2](PF6)2(1) and [Ni6(μ6-dpznda)4(NCS)2](PF6)2(2) (H2dpznda = N2,N7-di(pyrazin-2-yl)-1,8-naphthyridine-2,7-diamine) were synthesized and structurally characterized. Both the two complexes consist of a linear metal chain and four supporting ligands which are helically wrapped around the metal core. The single crystal X-ray structural analysis showed that the complex 1 belonged to rhombohedral system, space group R-3 with a = b = 34.2051(8), c = 20.7751(5) Å, V = 21050.2(9) Å3 and Z = 9. Direct-current magnetic susceptibility measurements showed weak antiferromagnetic interactions with coupling parameters of g = 2.04 and J = −8.27 cm−1 for 1 and g = 2.02 and J = −12.62 cm−1 for 2, respectively (Ĥ = -JŜ1Ŝ2, S1 = S2 = 1). The decrease of magnetic moments at low temperature was partly attributed to ZFS. The electrochemical study on complex 1 shows rich features and facility to reduction in its cyclic voltammogram by displaying four reversible redox couples at E1/2 = +0.01, −0.29, −0.64 and −0.73 V (vs. Ag/AgCl).