Octahedral vanadium oxide compounds

Spectra of octahedral vanadium(V) oxide compounds are presented in Figure 2. Undistorted vanadium(V) oxide compounds do not exist, and all vanadia octahedra are highly distorted, which give rise to short V-0 bonds. This is reflected in the Raman band position for the distorted octahedral vanadium oxide compounds which always occur in the 900-1000 cm region. The vanadia structure in 2 5 approaches a square-pyramidal coordination and the individual vanadia are linked... 

Another vanadium oxide that has received much attention is LiVaOs, which has a layer structure composed of octahedral and trigonal bipyramidal ribbons that can be swelled just like other layered compounds and can intercalate lithium. Here again, the method of preparation is important to its electrochemical characteristics. West et al. made a systematic study of the impact of synthesis technique on capacity and cycling and showed that amorphous material increased the capacity above 2 V from 3—4 lithium per mole of LiVsOs at low current drains, 6—200 fiAlcm. ... 

Vanadium(II) compounds are usually prepared by reduction of acidic solutions of higher oxidation states. The usual geometry is octahedral and the electronic spectra often show three d-d spin-allowed bands. These spectra, as well as those of tetrahedral and linear complexes, have been reviewed.58 For this cr configuration, a spin-only magnetic moment of 3.87 BM is expected. Slow substitution can be predicted for vanadium(II) complexes but such reactions are not as slow as those for the isoelectronic Crm ions. 

The Raman spectra oT model vanadium(V) oxide compounds are very sensitive to vanadium oxygen coordination. A distinct trend in the Raman spectra oT the reference tetrahedral and octahedral vanadium(V) oxide compounds is observed. Vanadium oxide is Tound to interact dit-ferently with the ditterent alumina supports. On the 7-AI2O3 support, the surtace vanadium oxide overlayer consists oT polymeric tetrahedra and distorted... 

Although many vanadium(III) complexes are unstable towards air, there are quite a few compounds in this oxidation state, most with octahedral geometry. However, remarkable seven-coordinate complexes were also characterized. 

The compound [VCl3(terpy)] is a paramagnetic, octahedral complex formed in the reaction of VCI3 (100) or [VCl3( BuNC)3] (408) with terpy. A bis(terpy)vanadium(III) complex is presumably the product of oxidation of [V(terpy)2] (49). A red polynuclear complex is formed from the reaction of aqueous vanadium(III) solutions with one equivalent of terpy (49). 

Vanadium compounds exist in a variety of formal oxidation states from -3 to +5. Their coordination number varies from 3 to 8. The stereochemistry depends on their oxidation state V(II) 6-coordinate octahedral, V(III) 3-7-coordinate (V[CH(SiMe3)2]3 3-coordinate planar), V(rV) 4-6 or 8-coordinate (V(CH2SiMe3)4 4-coordinate tetrahedral, VO(acac)2 5-coordinate tetragonal), V(V) 4-7-coordinate (VOCI3 4-coordinate tetrahedral). Standard electrode potential in acidic aqueous solution is as follows V + -F 2e- = V-1.19V, V + -F e =... 

All of the above compounds are oxides. The application of the fluorine route already described for AlPOs and GaPOs has shown that it is also possible to obtain open framework structures with fluoride in the VPOs. This led to the discovery by Riou and Ferey [72] of the first open-framework fluorovanado(V)phosphate, ULM-7 or (H3N(CH2-CH2)NH3)[(V 02)2(P04)F], in which the building units are V2P trimers. Vanadium exhibits both octahedral and square pyramidal coordination, and fluoride ion is shared between them. The three-dimensional network generated by comer-sharing of these trimers, exhibits 10-membered rings occupied by diprotonated amines. 

Monomeric species M OR-tert)x have been characterized for titanium, vanadium, chromium, zirconium, and hafnium (x = 4) and for niobium and tantalum (x == 5). With chromium it was found that limiting Cr(III) to coordination number 4 in the dimeric Cr2(OBu )e caused instability and a remarkable facility toward valency disproportionation or oxidation to the stable quadricovalent Cr(OBu )4 (8, 9). In contrast, molybdenum formed a stable dimeric tri-tert-butoxide (Bu O)3Mo=Mo-(OBu )3 which is diamagnetic and presumably bound by a metal-metal triple bond (10, II). Yet another interesting feature of chromium is the synthesis of a stable diamagnetic nitrosyl Cr(NO) (OBu )3 in which the nitric oxide is believed to act as a three-electron donor with formation of a four-coordinated low spin chromium (II) compound (12). The insta-bihty of Cr2(OBu )e and the stability of both Cr(NO) (OBu )3 and Cr(OBu )4 must result from the steric effects of the tertiary butoxo groups since the less bulky normal alkoxo groups form very stable polymeric [Cr(OR)3]a. compounds in which the Cr(III) has its usual coordination number of 6 (octahedral). 

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