[Et3PH][W4O3Cl7(PEt3)3]. A 12-electron tetrahedral tungsten cluster with an interesting arrangement of ligands

From the reaction between W2Cl6(PEt3)2 and H2O in tetrahydrofuran the dark green crystalline compound [Et3PH][W4O3Cl7(PEt3)3] was obtained and characterized by X-ray crystallography. At −155° the cell dimensions werea=b=c=20.392(3) A,Z=8,dcalcd=2.36 g cm−3 in the space group I23. The compound is a triethylphosphonium salt of the [W4O3Cl7(PEt3)3]− anion. The latter contains a tetrahedron of tungsten atoms with W−W=2.61 A (ave) and may be viewed as a W3(μ-Cl)3Cl3(PEt3)3 cluster capped by ad0-[WO3Cl]− unit and this has proved useful in examining the bonding within the cluster by use of the M.O. calculational method of Fenske and Hall. The cluster anion has crystallographically imposed C3v symmetry. Theoxo-groups bridge the tungsten atoms in a notably asymmetric manner W−O=1.87(2) A and 2.04(2) A with the shorter distances being involved with the capping [WO3Cl]− unit. The W−P bonds lie in the W3(μ3-Cl)3 plane and the three terminal W−Cl bonds are trans to theoxo-bridges.