title: Synthesis, spectral, and structural characterizations of imidazole oxalato molybdenum(IV/V/VI) complexes.
abstract: Substitutions of trans-Na(Him)[Mo(2)O(4)(ox)(2)(H(2)O)(2)]·H(2)O (1) and trans-(Him)(2)[Mo(2)O(4)(ox)(2)(H(2)O)(2)] (2) with imidazole result in the formation of the mixed-ligand molybdenum complexes cis-Na(2)[Mo(2)O(4)(ox)(2)(im)(2)]·4.5H(2)O (3), cis-K(2)[Mo(2)O(4)(ox)(2)(im)(2)]·3H(2)O (4), respectively (H(2)ox = oxalic acid; im = imidazole). Further reduction of cis-K(2)[Mo(2)O(4)(ox)(2)(im)(2)]·3H(2)O (4) gives a trinuclear molybdenum(IV) complex K(Him)[Mo(3)O(4)(ox)(3)(im)(3)]·3H(2)O (5), which contains an incomplete cubane cluster [Mo(IV)(3)O(4)](4+). Two novel trinuclear mixed-valence imidazole compounds [Mo(3)O(8)(im)(4)](im)·H(2)O (6) and [Mo(3)O(8)(im)(4)]·H(2)O (7) were obtained by the reduction of (Him)(4)[Mo(8)O(26)(im)(2)] (8). Both 6 and 7 contain a novel Mo(VI)O(4)(Mo(V)(2)O(4)) center, where the [Mo(V)(2)O(4)](2+) unit is linked by [Mo(VI)O(4)](2-) anion. The Mo-Mo bond distances in 1-7 decrease with the decrease of oxidation state of molybdenum. Solid and solution NMR spectra show that imidazole molybdenum compounds 6-8 fully dissociate in solution, where solvated imidazole and imidazolium groups in 6 and 8 could be served as internal references in their solid (13)C NMR spectra. Furthermore, mixed-ligand molybdenum species 3 and 4 are stable in water. Stabilities of 3 and 4 in solution may be attributed to the strong coordination of bidentate oxalate and the formation of hydrogen bond. Dimers 2 and 4 display quasi-reversible redox process, while trimer 6 is irreversible. Bond valence calculations for 1-8 are consistent with their oxidation states of molybdenum atoms. Calculation of the oxidation state in recent structure of iron molybdenum cofactor [MoFe(7)S(9)C(R-homocit)] (FeMo-co) is 3.318.
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China.
authors.forename: Quan-Liang
authors.initials: QL
authors.lastname: Chen
authors.forename: Hong-Bin
authors.initials: HB
authors.lastname: Chen
authors.forename: Ze-Xing
authors.initials: ZX
authors.lastname: Cao
authors.forename: Zhao-Hui
authors.initials: ZH
authors.lastname: Zhou
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D019281:Dimerization; D007093:Imidazoles / Q000737:chemistry*; D008024:Ligands; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D056831:Coordination Complexes; D007093:Imidazoles; D008024:Ligands; C029899:imidazole; D008982:Molybdenum