Yang Zhiyong, Gould Edwin S
Department of Chemistry, Kent State University, Kent, Ohio 44242, USA.
Dalton Trans. 2006 Jul 28(28):3427-30. doi: 10.1039/b516547b. Epub 2006 Apr 19.
The reactions of aqueous H2MoO4 at low pH with titanium(II), titanium(III), europium(II), vanadium(II), and germanium(II), as monitored at 430 nm, give biphasic profiles featuring a sharp rise in absorbance followed by a marked decrease (Fig. 1). The final product is the dimeric Mo(V) cation, [Mo2O4]2+, and the strongly absorbing intermediate is taken as a monomeric Mo(V) species. The molar absorbances of the transients from different reductants are not the same, nor are the rate laws governing the fadings. None of the decay curves exhibits evidence of a second order dependence on the transient. The kinetic behaviors of these systems are consistent with the intervention of successor complexes of the type [Chemical structure: see text], (formed by inner sphere reductions of Mo(VI)), which decompose, via first-order processes, to a monomeric Mo(V) species. The latter then experiences rapid dimerization, which is kinetically silent. The possibility that Ge(II) bypasses the unstable tripositive state by reducing Mo(VI) to Mo(IV) (which then undergoes rapid Mo(VI)-Mo(IV) comproportionation) is considered.
在低pH值下，用430 nm监测H₂MoO₄水溶液与钛（II）、钛（III）、铕（II）、钒（II）和锗（II）的反应，得到双相曲线，其特征是吸光度急剧上升，随后显著下降（图1）。最终产物是二聚体Mo（V）阳离子[Mo₂O₄]²⁺，强吸收中间体被认为是单体Mo（V）物种。来自不同还原剂的瞬态的摩尔吸光度不同，控制褪色的速率定律也不同。没有一条衰减曲线显示出对瞬态的二级依赖性。这些体系的动力学行为与[化学结构：见正文]类型的后继络合物的介入一致，（由Mo（VI）的内球还原形成），它们通过一级过程分解为单体Mo（V）物种。后者随后经历快速二聚化，这在动力学上是不明显的。考虑了锗（II）通过将Mo（VI）还原为Mo（IV）（然后经历快速的Mo（VI）-Mo（IV）歧化反应）绕过不稳定三价态的可能性。
