Synthesis of hetero- and homo-multinuclear complexes with a tetracyanonickelate anion: structural characterization [Cu(bcen)Ni(CN)₄]₂

Two new complexes [Cu(bcen)Ni(CN)₄]₂ (1) and [Ni(bcen)Ni(CN)₄] (2) where bcen is 4,7-diazadecanediamide, were synthesized by reaction of equimolar amounts of M(NO₃)₂ (M = Cu and Ni), bcen ligand and K₂[Ni(CN)₄]. Single-crystal X-ray diffraction analysis of compound 1, shows that the bcen ligand acts as a tridentate chelate, coordinating to the Cu(II) ion via the two nitrogen atoms of the amine groups and one oxygen atom of one amide group, and the other amide unit is left uncoordinated. The coordination geometry around the Cu(II) ions is five coordinate with a distorted square pyramid geometry, comprising two nitrogen atoms and one oxygen atom belonging to the bcen ligand and two nitrogen atoms of the cyano groups of two Ni(CN)₄^2– units. The distance between the copper ion and the amide oxygen of the dangling arm of an adjacent tetranuclear species is within the expected range for an axial Cu–O bond, and hence suggests that the amide oxygen of an adjacent tetranuclear complex may weakly coordinate to the copper ion in an axial position. These contacts link the tetranuclear species into infinite chain polymers.