Synthesis, crystal structure and magnetic properties of the first structurally characterized 1,2-dithiocroconato-containing Cu(II) complex, {[Cu(bpca)(H2O)](2)[Cu(1,2-dtcr)(2)]}center dot 2H(2)O

The first crystal and molecular structure of a transition metal complex containing 1,2-dithiocroconate (1,2-dtcr, dianion of 1,2-dimercaptocyclopent-1-ene-3,4,5-trione),{[Cu(bpca) (H2O)](2)[Cu(1,2-dtcr)(2)]}. 2H(2)O (where bpca is the bis(2-pyridylcarbonyl)amide anion), has been determined by single crystal X-ray diffraction methods. The compound crystallizes in the monoclinic system, space group P2(1)/c, with a=11.661(3), b=20.255(6), c=8.265(3) Angstrom, beta=107.26(2)degrees and Z=2. The structure is formally built of [Cu(1,2-dtcr)(2)](2-) and [Cu(bpca) (H2O)](+) ions and water of hydration. The copper atom of the anion is situated at a crystallographic inversion centre, bonded to four sulfur atoms in a planar, approximately square arrangement. In the cation the copper equatorial plane is formed by the three nitrogen atoms of the bpca ligand and a water oxygen atom. In addition there is a very weak axial bond to one of the sulfur atoms of a 1,2-dtcr ligand in the anion. Through these latter weak bonds each anion is connected to, and sandwiched between, two cations, resulting in neutral, trinuclear, centrosymmetric formula units. The triple-decker molecules are arranged in stacks along the crystallographic a-axis creating close contacts between the terminal copper atoms and bpca groups of the neighbouring molecules. This intermolecular interaction is, however, too weak to define the structure as a chain compound. The distance between adjacent copper atoms within the trinuclear unit is 4.189(1) Angstrom, while the shortest intra-stack metal-metal separation between terminal copper atoms is 5.281(1) Angstrom. Variable-temperature magnetic susceptibility measurements in the temperature range 4.2-140 K reveal that a Curie law is followed; with three non-interacting copper(II) ions in the formula unit.