The reaction of SeCl4, with transition metal tetrachlorides. Synthesis and crystal structures of (SeCl3)(2)MCl(6) with M=Zr,Hf,Mo,Re

The transition metal tetrachlorides ZrCl4, HfCl4 and MoCl4 react with SeCl4 in closed ampoules at temperatures of 140 degrees C to (SeCl3)(2)MCl(6) (M = Zr, Hf, Mo) which are all isotypic and crystallize in the (SeCl3)(2)ReCl6 structure type (orthorhombic, Fdd2, Z = 8, lattice constants for M = Zr: a = 1165.7(1) pm, b = 1287.2(2) pm, c = 2180.2(2) pm; for M = Hf: a = 1162.9(2) pm b = 1285.0(2) pm, c = 2178.2(3) pm; for M = Mo: a = 1153.8(1) pm, b = 1267.7(1) pm, c = 2147.4(2) pm). The Cl- ions form a hexagonal closest packing with one fourth of the octahedral holes filled by Se4+ and M(4+) in an ordered way. The MCl(6) octahedra are regular, the SeCl6 octahedra are distorted with 3 short and 3 long Se-Cl bonds (mean 215 pm and 287 pm). The structures can thus be regarded as built of SeCl3+ and MCl(6)(2-) ions. Magnetic susceptibility measurements show for M = Zr the expected diamagnetic behavior, for M = Mo and Re paramagnetic behavior according to the Curie-Weiss law with magnetic moments of 2.5 B.M. for M = Mo and 3.7 B.M. for M = Re corresponding to 2 and 3 unpaired electrons respectivly.