(Se4)2[MO2O2Cl8][MCl6] (M = Zr, Hf) -: Tetraselenium(2+)halometalates with two different anions

The reaction of Se4[Mo2O2Cl8] with Se-4[MCl6] (M = Zr, Hf) or of Se, SeCl4, MOOCl4, and MCl4 (M = Zr, Hf) at 120degreesC in seated evacuated glass ampoules gives (Se-4)(2)[Mo2O2Cl8][MCl6] (M = Zr, Hf) in the form of dark-green, air sensitive crystals in quantitative yield. The crystal structure analyses of both isotypic compounds (monoclinic, P2(1)/c, Z = 2, a = 1336(2), b = 716(1), c = 1518(4) pm, beta = 106.0(2)degrees for M = Zr; a = 1334.1(8), b = 715.03(9), c = 1518.2(3) pm, beta = 106.00(2)degrees for M = Hf) show the presence of square-planar Se-4(2+), of dinuclear [Mo2O2Cl8](2-), and of almost regular octahedral [MCl6](2-) ions. X-ray crystallographic investigations on (Se-4)(2)[Mo2O2Cl8][ZrCl6] give no hint for solid state phase transitions between -160 and 200degreesC. This is in contrast to the related compounds Se-4[Mo2O2Cl8] and Se-4[ZrCl6] which both undergo phase transitions accompanied by reorientation of the cations and anions. (Se-4)(2)[Mo2O2Cl8][ZrCl6] is paramagnetic and obeys the Curie-Weiss law with a Weiss constant of -4(7) K indicating only weak interaction between the paramagnetic centres. The magnetic moment of 1.7(1) mu(B) is consistent with the presence of Mo-V (d(1) configuration) and supports the ionic formula.