Unsymmetrically substituted pyrazolates: nickel(II) complexes of a novel dinucleating ligand providing both N- and S-rich co-ordination spheres ‡

An unsymmetric pyrazolate ligand with different chelating side arms in the 3 and 5 positions of the heterocycle {3-[(EtSCH2CH2)2NCH2]-5-[(Et2NCH2CH2)2NCH2]C3N2H2 (HL1)} and its symmetrical analogue {3,5-[(EtSCH2CH2)2NCH2]2C3N2H2(HL2)} have been prepared. Upon reaction with NiCl2·6H2O they afforded dinuclear complexes [Ni2L1Cl3] 2 and [Ni2L2Cl3] 1 that contain both a bridging pyrazolate and a bridging chlorine atom. While all nickel(II) ions within the N2S2 compartments of the primary ligands are six-co-ordinate, one of the amino side arms of L1 in the former complex is non-co-ordinating, leaving the respective nickel centre in a square-pyramidal environment. This dangling arm is co-ordinated to the metal ion upon treatment of 2 with NaBPh4 due to substitution of the terminal chlorine atom to form [Ni2L1Cl2][BPh4] 3. All new complexes were characterised by means of X-ray crystallography; 2 and 3 represent rare examples of dinuclear complexes exhibiting various kinds of asymmetry. The electrochemical and magnetic properties of the complexes are reported.