Novel mixed-valence Cu compounds formed by Cuii dimers with double oximato bridges: in situ formation of anionic layer [Cu2(SCN)3]nn−

Abstract

Two new N₃O donor ketoxime Schiff bases (HL¹ and HL²) have been synthesized by condensing N,N-dimethylethylenediamine with diacetylmonoxime and benzilmonoxime, respectively in a 1 : 1 ratio. Reaction of Cu(ClO₄)₂·6H₂O with HL¹ resulted in a discrete oximato-bridged dinuclear Cu^II complex [Cu₂(L¹)₂(H₂O)₂](ClO₄)₂ (1). The same reaction in presence of NaSCN affords the complex {[Cu^II₂(L¹)₂][Cu^I₄(μ_1,3-SCN)₄(μ_1,1,3-SCN)₂]}_n (2), where partial Cu^II→Cu^I reduction is observed. In 2, arrays of [Cu^II₂(L¹)₂]²⁺ cationic units are inserted in between 2D {[Cu^I₄(SCN)₆]²⁻}_n layers and connected via μ_1,1,3-SCN⁻ links, thus forming a 3D network. On the other hand, reaction of Cu(CH₃COO)₂ and HL² in the presence of NaSCN gave rise to a mixed-valence pentanuclear cluster {[Cu^II₂(L²)₂(NCS)]₂[Cu^I(SCN)(μ_1,1-SCN)(μ_1,3-SCN)]} (3) where Cu^II is also partly reduced to Cu^I. In compound 3, two cationic [Cu^II₂(L²)₂(NCS)]⁺ units are bridged by the anionic [Cu^I(SCN)₃]²⁻ unit through long Cu–SCN linkages. The ligands and the complexes have been characterized by elemental analysis, UV/Vis and IR spectroscopy. The complexes are further characterized by single crystal X-ray diffraction and variable temperature magnetic (VTM) studies. Finally a complete magneto-structural correlation has been established between compounds 1–3 and all the characterized Cu dimers with a double NO bridge.