Open-Shell Organometallics as a Bridge between Werner-Type and Low-Valent Organometallic Complexes. The Effect of the Spin State on the Stability, Reactivity, and Structure.

Structural aspects of molybdenum(IV), molybdenum(V) and molybdenum(VI) complexes

The Coordination and Bioinorganic Chemistry of Molybdenum

Preparation of the di-µ-selenido-dimolybdenum(V) complex [Mo2O2(µ-Se)2(cys)2]2–(cys =L-cysteinate dianion), and the related aqua ion [Mo2O2(µ-Se)2(H2O)6]2+, has enabled the trimolybdenum(IV) incomplete cuboidal Mo3OxSe4–x4+(x= 0–3) complexes [Mo3(µ3-Se)(µ-Se)3(H2O)9]4+[Mo3(µ3-Se)-(µ-O)(µ-Se)2(H2O)9]4+, [Mo3(µ3-Se)(µ-O)2(µ-Se)(H2O)9]4+, and the mixed-valence (average oxidation state 3.25) cuboidal [Mo4(µ3-Se)4(H2O)12]5+ complex to be obtained for the first time. The crystal structures of Na[NMe4][Mo2O2(µ-Se)2(cys)2]·7H2O, [NMe4]5-(pts)5·14H2O (pts–= toluene-p-sulfonate) have been determined. Electrolytic reduction of [Mo4(µ3-Se)4(H2O)12]5+ in 2 M Hpts gives quantitatively the air-sensitive tetramolybdenum(III) analogue [Mo4(µ3-Se)4(H2O)12]4+(Ef°= 190 mV). Similarly the 5+ ion can be oxidised to the 6+ state (Ef°= 790 mV). Compared to analogous Mo-S clusters, Mo-Se clusters exhibit identical structures but with longer bond distances, red-shifted absorption bands, and in the case of the cuboidal aqua complexes less-positive reduction potentials. By analogy with [Mo3S4(H2O)9]4+, [Mo3MSe4(H2O)10]4+ heterometal cuboidal and related complexes are obtained. The edta(=N,N,N′N′-ethylenediamine-tetraacetate) complex of the 5+ cube [Mo4Se4(edta)2]3– has been prepared, and reduction potentials for the corresponding core 5+/4+ and 6+/5+ couples determined as –40 and 650 mV respectively.

Preparation, structure and properties of dinuclear, trinuclear incomplete cuboidal and cuboidal molybdenum-selenium cluster complexes

Mo(V) aqua-chloro complexes in hydrochloric acid solutions have been studied by means of Mo K- and L2,3-edge X-ray absorption and Raman spectroscopic methods. The solid compounds (HPPh3)2[MoOCl5] (1), 6[MoOCl4(H2O)]-·10(pyH)+·4Cl- (2), and (pyH)2[Mo2O4Cl4(trans-OH2)2] (3) were used for structural comparisons. The compound 2 crystallizes in the orthorhombic space group Pmma (no. 51) with a = 21.398(3), b = 8.057(4), c = 13.330(4) A, and Z = 4. In 0.2 M solutions of MoCl5 in 7.4−9.4 M HCl the mononuclear [MoOCl4(OH2)]- complex dominates with the bond distances MoO 1.66(2) A, Mo−Cl 2.38(2) A, and Mo−OH2 2.30(2) A. Its Raman band at 994 cm-1 for the MoO symmetric stretching vibration is closer to that of 2 (988 cm-1) than of 1 (969 cm-1). The Mo K-edge EXAFS spectrum for 0.2 M MoCl5 in 1.7 M HCl solution reveals a dinuclear [Mo2O4Cl6-n(OH2)n]n-4 (n = 2, 3) complex with a double oxygen bridge and the average distances MoO 1.67(2) A, Mo−(μ-O) 1.93(2) A, Mo−Cl 2.47(3) A, Mo−Mo 2.56(2) A, and a short Mo−OH2 dista...

Structural characterization of molybdenum(V) species in aqueous HCl solutions.

Synthesis, infrared spectra, magnetic properties, and electronic structure of di-.mu.-oxo- and di-.mu.-oxo-bis(di-.mu.-oxo)-bridged oxomolybdates(V) and their theoretical interpretation

Results of SCCC MO calculations for the dimeric oxygen double-bridged [Mo2O4Cl4(H2O)2]2−ion are reported. On the basis of these results the previously reported spectra and magnetic properties may be explained. The strong direct molybdenum — molybdenum interaction in the Mo2O
 4
 2+
 core was proved to exist.

Leszek. Natkaniec

Papers

Synthesis, infrared spectra, magnetic properties, and electronic structure of di-.mu.-oxo- and di-.mu.-oxo-bis(di-.mu.-oxo)-bridged oxomolybdates(V) and their theoretical interpretation

The electronic structure of the oxygen double-bridged μμ′-dioxo-bis(oxodichloroaquo)dimolybdate (V)-ion by SCCC MO method