Vanadate divanadate

Figure 7 The uranophane sheet anion topology (a) and the uranophane-type sheet (b) found in some diamine-templated layered uranyl vanadates (c), in structure of (U02)3(V0 )2.5H20 where layers are connected by UO7 pentagonal bipyramids (d), in diamine-templated 3-D uranyl vanadates (e), in uranyl divanadate U2V2O11 (f). The occupation of the sqnares of the uranophane anion topology by the VO5 entities results in 2-D layers (g) that are linked into a 3-D framework inUVOj.

The formation constants for the monoesters [x = 1 in Equation (2.11)] are small, typically around 0.1 m for alkyl alcohols, and an order of magnimde more for phenols.I ] Esters derived from divanadate, such as [HV205(0R)] , have also been noted. In analogy with the vanadates, the esters are subject to protonation-deprotonation equilibria. 

Left V NMR spectra of vanadate in a lyotropic mesophase (dodecanoate + tetradecyltrimethyl-ammonium at varying ratios of the two components).The two components correspond to mono-(low field) and divanadate (high field). Right first-derivative NMR spectrum of V0(0/Pr)3 dissolved in the liquid crystal MBBA (4-methoxybenzylidene-4 -butylamine) at a concentration of 8.3%. 

Figure 6 pH-dependent 131.5 MHz V NMR spectra of the system vanadate/H+/alanylhistidine (Ah). The resonances correspond to decavanadate (Vio), vanadate-Ah complexes (V-Ah), monovanadate (Vi), divanadate (V2), tetravanadate (V4) and pentavanadate (V5) in chemical equilibrium with each other. Reproduced with permission from Elvingsn K, Fritzsche M, Rehder D and Pettersson L (1994) Potentiometric and NMR study of aqueous equilibria in the H -vanadate(V)-alanylhistidine system. Acta Chimica Scandi-navica 48 881. 

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