Synthesis, crystal structure and magnetic properties of [Cu6(tidah)2Cl10(H2O)4]·6H2O [Htidah = 1,1,6,6-tetrakis-(imidazol-2-yl)-2,5-diazahexane], a unique imidazolato- and chloro-bridged hexanuclear copper(II) compound

Abstract

The novel hexanuclear copper(II) compound [Cu₆(tidah)₂Cl₁₀(H₂O)₄]·6H₂O was obtained by the reaction of copper(II) chloride with the polyimidazole 1,1,6,6-tetrakis(imidazol-2-yl)-2,5-diazahexane (Htidah). This compound crystallizes in the monoclinic space group P2₁/c, with a= 7.915(5), b= 16.745(6), c= 20.954(8)Å, β= 95.41(4)°, Z = 2. The structure was solved using direct methods and refined on F by full-matrix least squares. Convergence was reached at R= 0.097 for 991 reflections with l > 2σ(l). Structure analysis shows a complex molecule with six copper ions in three different co-ordination environments. The asymmetric unit, which comprises half a molecule, consists of a trinuclear subunit. In each subunit two copper ions are linked by an imidazolate anion, the Cu ⋯ Cu distance is 5.7226(8)Å. The two subunits are linked by four asymmetric copper to chloride to copper bridges, with Cu ⋯ Cu distances of 4.053(9) and 4.696(9)Å. The magnetic super-exchange interaction via the bridging imidazolate ligand seems to be the most important magnetic interaction in this molecule. A fit of the magnetic susceptibility vs. the temperature, in the 6–250 K range, shows a fair agreement for a dinuclear S =½ species, with an energy separation between the spin singlet ground state and the triplet excited state of 90 cm^–1.