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

Abstract

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.