Trapping tetramethoxyzincate and -cobaltate(II) between Mo₂⁴⁺ units

Two compounds of a new type, [Mo₂](CH₃O)₂M(CH ₃O)₂[Mo₂] where [Mo₂] is an abbreviation for Mo₂[(p-MeOC₆H₄)- NCHN(p-MeOC₆H₄)]₃ and M = Zn (1) and Co (2), are reported. Discrete [M(OR)₄]^2- ions, either as such or in the μ₂,η⁴ role, have not heretofore been described. In these compounds they have distorted tetrahedral structures and bridge two [Mo₂] groups in much the same way as did SO₄^2-, MoO₄^2-, and WO₄^2- ions in other recently reported compounds (Cotton, F. A.; Donahue, J. P.; Murillo, C. A. Inorg. Chem. 2001, 40, 2229). The ¹H NMR spectrum of 1 and the visible spectrum and magnetic properties of 2 are consistent with these structures. The M(OCH₃)₄ bridges are moderately effective in coupling the two [Mo₂] redox centers. Compounds 1 and 2 may also be viewed as having Zn^∥ and Co^∥ centers tetrahedrally coordinated by the bidentate ligand [Mo₂[(p-MeOC₆H₄)NCHN (p-MeOC₆H₄)]₃- (OMe)₂]^-. From that point of view they may be compared with Zn(DPM)₂ and Co(DPM)₂ (3), where DPM is the anion of dipivaloylmethane. For purposes of comparison, 3 has been fully characterized structurally, spectroscopically, and magnetically. Close analogies between 2 and 3 are shown to exist.