Characterization of two conformers in the co-ordination chemistry of 3,4-bis(cyanamido)cyclobutane-1,2-dione dianion: syntheses, crystal structures, and electrochemical study of nickel(ii) complexes

Abstract

Three complexes [Ni(Him)₄(3,4-NCNsq)(H₂O)]·H₂O 1, {[Ni₂(Him)₂(3,4-NCNsq)₂(H₂O)₆]·8H₂O}_n2 and [Ni(tren)(3,4-NCNsq)]_n3, where 3,4-NCNsq²⁻ = 3,4-bis(cyanamido)cyclobutane-1,2-dione dianion and Him = imidazole, have been synthesized and characterized by electronic absorption and IR spectroscopies. The structures of the three complexes have been determined by X-ray crystallography and, for the first time, two conformations of the ligand 3,4-NCNsq²⁻ have been evidenced. Complex 1 consists of mononuclear entities and complexes 2 and 3 are made of infinite chains with nickel(II) atoms bridged by the bis monodentate 3,4-NCNsq²⁻ ions. The magnetic properties of the three complexes have been investigated in the 2–300 K temperature range (μ_eff = 2.84 to 3.12 μ_B for 1, μ_eff = 2.32 to 3.46 μ_B for 2 and μ_eff = 2.74 to 3.13 μ_B for 3). Their redox properties are discussed and compared to those of the free 3,4-NCNsq²⁻ dianion.