Synthesis, characterisation and crystal structures of new nickel complexes in S4 coordination spheres; an unprecedented rearrangement during ligand synthesis

Abstract

Two new nickel(II) complexes were synthesized with an S₄ coordination environment. These complexes were synthesized by in situ deprotection of thiouronium salts in the presence of nickel(II). The ligands used are 4-mercapto-3,3-methyl-1-phenyl-2-thiabutane (Hbsms) and α,α′-bis(4-mercapto-3,3-methyl-2-thiabutyl)-o-xylene (H₂xbsms). The former is a didentate ligand containing one thioether and one thiolate group and the latter is a dithioether dithiolate tetradentate ligand. The differences between these ligands upon coordination to nickel have been investigated. During the synthesis of these ligands, an unprecedented spontaneous rearrangement occurs, which is very fast and selective to a single product. The complexes were characterized by analytical, spectroscopic and electrochemical methods. The geometry of the nickel complexes is square planar according to the single-crystal X-ray structures. In [Ni(bsms)₂] the two ligands are coordinated with the thiolates in trans positions towards each other; in [Ni(xbsms)] the thiolates are in enforced cis positions. [Ni(bsms)₂] crystallizes in the triclinic space group P and has one centrosymmetric molecule in the unit cell. [Ni(xbsms)] crystallizes in the monoclinic space group P2₁/c with two independent molecules in the asymmetric unit, however, the differences between these two molecules are very small. The Ni–S distances are 2.1730(4)–2.1909(6) Å and in the common range for thiolates and chelating thioethers.