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.