(Se4)2[Mo2O2Cl8][MCl6](M = Zr,Hf) — Tetraselenium(2+)Halometalates with two Different Anions

The reaction of Se₄Mo₂O₂Cl₈] with Se₄MCl₆] (M = Zr, Hf) or of Se, SeCl₄, MoOCl₄, and MCl₄ (M = Zr, Hf) at 120 °C in sealed evacuated glass ampoules gives (Se₄)₂Mo₂O₂Cl₈]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, P2₁/c, Z = 2, a = 1336(2), b = 716(1), c = 1518(4) pm, β = 106.0(2)° for M = Zr; a = 1334.1(8), b = 715.03(9), c = 1518.2(3) pm, β = 106.00(2)° for M = Hf) show the presence of square‐planar Se₄²⁺, of dinuclear Mo₂O₂Cl₈]^2—, and of almost regular octahedral MCl₆]^2— ions. X‐ray crystallographic investigations on (Se₄)₂Mo₂O₂Cl₈]ZrCl₆] give no hint for solid state phase transitions between —160 and 200 °C. This is in contrast to the related compounds Se₄Mo₂O₂Cl₈] and Se₄ZrCl₆] which both undergo phase transitions accompanied by reorientation of the cations and anions. (Se₄)₂Mo₂O₂Cl₈]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) μ_B is consistent with the presence of Mo^V (d¹ configuration) and supports the ionic formula.