SYNTHESIS AND X-RAY STRUCTURE DETERMINATION OF [PPH4]2[CL3W(MU-SE(CL))(MU-SEPH)2WCL3].2CH2CL2 - SINGLE-CRYSTAL ESR STUDY OF A MIXED-OXIDATION-STATE BINUCLEAR TUNGSTEN(III) TUNGSTEN(IV) COMPLEX DISPERSED IN A DIAMAGNETIC CRYSTAL MATRIX

Reaction of WCl4(Me2S)2 with Me3SiSePh in CH2Cl2 solution, followed by addition of PPh4Cl, yields a mixture of the two compounds [PPh4]2[Cl3W(μ-Se)(μ-SePh)2WCl3]-2CH2Cl2 (1) and its mixed-oxidation-state analogue, [PPh4]2[Cl3W(μ-Cl)(μ-SePh)2WCl3]·2CH2Cl2 (2). The compounds are isostructural and isomorphous and in some preparations cocrystallize. Crystals of a sample containing primarily 1 were subjected to an X-ray structure determination. Crystal data: monoclinic, space group, C2/c, a = 22.838 (3) Å, b = 12.208 (2) Å, c = 24.313 (5) Å, β = 104.64 (1)°, V= 6558.8 Å3, Z = 4, R = 0.051 (Rw = 0.046) for 357 parameters and 3742 unique observed reflections. The geometry of the anion of 1 is confacial bioctahedral, with three Se atoms in the bridging positions. The W–W bond length is 2.5641 (8) Å, consistent with the presence of a formal double bond between the two d2 metal centers. 77Se NMR studies showed two resonances, consistent with this structure being retained in solution. An ESR study of the powdered crystals of one sample indicated the presence of a paramagnetic impurity, identified as the anion of 2. This enabled us to carry out a single-crystal ESR study of this anion in a diamagnetic matrix of complex 1. There is a very large anisotropy in the crystal g values, with one (that close to the W–W vector) being considerably greater than 2. Hyperfine interactions with 183W and 31,37Cl are observed in some orientations, a fact which is used to assign a ground-state electronic configuration to the ion. © 1990, American Chemical Society. All rights reserved.