Vanadium compounds

[[File:Vanadiumoxidationstates.jpg|thumb|right|upright|From left: [V(H 2 O) 6 ] 2+ (lilac), [V(H 2 O) 6 ] 3+ (green), [VO(H 2 O) 5 ] 2+ (blue) and [VO(H 2 O) 5 ] 3+ (yellow). Vanadium compounds are compounds formed by the element vanadium (V). The chemistry of vanadium is noteworthy for the accessibility of the four adjacent oxidation states 2–5, whereas the chemistry of the other group 5 elements, niobium and tantalum, are somewhat more limited to the +5 oxidation state. In aqueous solution, vanadium forms metal aquo complexes of which the colours are lilac [V(H 2 O) 6 ] 2+ , green [V(H 2 O) 6 ] 3+ , blue [VO(H 2 O) 5 ] 2+ , yellow-orange oxides [VO(H 2 O) 5 ] 3+ , the formula for which depends on pH. Vanadium(II) compounds are reducing agents, and vanadium(V) compounds are oxidizing agents. Vanadium(IV) compounds often exist as vanadyl derivatives, which contain the VO 2+ center. Ammonium vanadate(V) (NH 4 VO 3 ) can be successively reduced with elemental zinc to obtain the different colors of vanadium in these four oxidation states. Lower oxidation states occur in compounds such as V(CO) 6 , and substituted derivatives. Vanadium pentoxide is a commercially important catalyst for the production of sulfuric acid, a reaction that exploits the ability of vanadium oxides to undergo redox reactions.…

[[File:Vanadiumoxidationstates.jpg|thumb|right|upright|From left: [V(H 2 O) 6 ] 2+ (lilac), [V(H 2 O) 6 ] 3+ (green), [VO(H 2 O) 5 ] 2+ (blue) and [VO(H 2 O) 5 ] 3+ (yellow).]] Vanadium compounds are compounds formed by the element vanadium (V). The chemistry of vanadium is noteworthy for the accessibility of the four adjacent oxidation states 2–5, whereas the chemistry of the other group 5 elements, niobium and tantalum, are somewhat more limited to the +5 oxidation state. In aqueous solution, vanadium forms metal aquo complexes of which the colours are lilac [V(H 2 O) 6 ] 2+ , green [V(H 2 O) 6 ] 3+ , blue [VO(H 2 O) 5 ] 2+ , yellow-orange oxides [VO(H 2 O) 5 ] 3+ , the formula for which depends on pH. Vanadium(II) compounds are reducing agents, and vanadium(V) compounds are oxidizing agents. Vanadium(IV) compounds often exist as vanadyl derivatives, which contain the VO 2+ center. Ammonium vanadate(V) (NH 4 VO 3 ) can be successively reduced with elemental zinc to obtain the different colors of vanadium in these four oxidation states. Lower oxidation states occur in compounds such as V(CO) 6 , and substituted derivatives. Vanadium pentoxide is a commercially important catalyst for the production of sulfuric acid, a reaction that exploits the ability of vanadium oxides to undergo redox reactions. The vanadium redox battery utilizes all four oxidation states: one electrode uses the +5/+4 couple and the other uses the +3/+2 couple. Conversion of these oxidation states is illustrated by the reduction of a strongly acidic solution of a vanadium(V) compound with zinc dust or amalgam. The initial yellow color characteristic of the pervanadyl ion [VO 2 (H 2 O) 4 ] + is replaced by the blue color of [VO(H 2 O) 5 ] 2+ , followed by the green color of [V(H 2 O) 6 ] 3+ and then the violet color of [V(H 2 O) 6 ] 2+ . Vanadium(V) forms various peroxo complexes, most notably in the active site of the vanadium-containing bromoperoxidase enzymes. The species VO(O) 2 (H 2 O) 4 + is stable in acidic solutions. In alkaline solutions, species with 2, 3 and 4 peroxide groups are known; the last forms violet salts with the formula M 3 V(O 2 ) 4 nH 2 O (M= Li, Na, etc.), in which the vanadium has an 8-coordinate dodecahedral structure. Twelve binary halides, compounds with the formula VX n (n=2..5), are known. VI 4 , VCl 5 , VBr 5 , and VI 5 do not exist or are extremely unstable. In combination with other reagents, VCl 4 is used as a catalyst for polymerization of dienes. Like all binary halides, those of vanadium are Lewis acidic, especially those of V(IV) and V(V). Many of the halides form octahedral complexes with the formula VX n L 6−n (X= halide; L= other ligand). Many vanadium oxyhalides (formula VO m X n ) are known. The oxytrichloride and oxytrifluoride (VOCl 3 and VOF 3 ) are the most widely studied. Akin to POCl 3 , they are volatile, adopt tetrahedral structures in the gas phase, and are Lewis acidic.

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