Crystal structure and magnetic properties of [{Cu(cyclam)}3{Fe(CN)6}2] · 6H2O, a cyano-bridged assembly with a rope-ladder chain structure

Abstract

The synthesis, crystal structure and magnetic properties of the cyano-bridged complex [{Cu(cyclam)}3{Fe(CN)6}2]·6H2O are reported. Its structure is made up of centrosymmetric S-shaped pentanuclear [{Cu(cyclam}3{Fe(CN)6)}2] units, in which three [Cu(cyclam)]2+ units are alternatively bridged by two trans-CN groups of [Fe(CN)6]3− anions and water molecules. The pentanuclear Fe2Cu3 units are held together by two complementary and very weak Fe–CN⋯Cu1 bonds, forming a rope-ladder chain along the c axis. The compound exhibits a ferromagnetic interaction between the Cu(II) and Fe(III) ions as a consequence of the orthogonality of their magnetic orbitals of σ and π nature, respectively. The magnetic data were fitted to the calculated magnetic susceptibility equation for a pentanuclear model, leading to the following magnetic parameters: J1=9.0(3)cm−1, J2=3.8(4)cm−1, g=2.2, θ=−1.2K. These results show that the interactions through the long Cu–N axial bonds are not so weak as is usually assumed.