Crystal structure and spectroscopic properties of a polynuclear complex between [bis(2-aminoethyl)amine]copper(II) and hexacyanoferrate(III)

Abstract

The addition of [Fe(CN)₆]^3– to [Cu(dien)]²⁺[dien = diethylenetriamine, bis (2-aminoethyl)amine] gives a polynuclear complex of formula 3[Cu(dien)]²⁺·2[Fe(CN)₆]^3–·6H₂O. The compound has been characterized by i.r., e.s.r., and reflectance spectra, and its crystal and molecular structure solved by single-crystal X-ray diffractometry. The dark green crystals are monoclinic, space group P2₁/c, with a= 20.332(6), b= 14.162(5), c= 14.932(5)Å, β= 96.29(3)°, and Z= 4. The structure has been refined by least-squares methods, using 2 518 independent reflections, to a conventional R of 0.062. It consists of two distinct ionic units. One is a polymer chain running parallel to the 2₁ screw axis and formed by cationic {2[Cu(dien)]·[Fe(CN)₆]}⁺ units in which the [Cu(dien)]²⁺ and [Fe(CN)₆]^3– ions are linked through cyanide bridges. In this unit, only four of the six CN^– groups around each iron are bonded to copper atoms of adjacent [Cu(dien)]²⁺ molecules, thus giving rise to both linear and non-linear Fe–CN–Cu linkages and to a square-based pyramidal co-ordination of nitrogen atoms around each copper atom. The other structural unit, {[Cu(dien)]·[Fe(CN)₆]}^–, is an anionic monomer formed by linking the [Cu(dien)]²⁺ and [Fe(CN)₆]^3– ions through only one cyanide bridge; one of the six water molecules co-ordinates to the Cu²⁺ to give five-co-ordination. Four water molecules per asymmetric unit of the complex participate in a hydrogen-bond system, both among themselves and with some of the nearest nitrogens of the anionic unit. Each of the other two water molecules interacts only with one nitrogen of the nearest hexacyanoferrate of the anionic unit.