vanadium are Lewis acidic, especially those of V(IV) and V(V). Many of the halides form octahedral complexes with the formula VXnL6−n (X= halide; L= other ligand). Many vanadium oxyhalides (formula VOmXn) are known. The oxytrichloride and oxytrifluoride (VOCl3 and VOF3) are the most widely studied. Akin to POCl3, they are volatile, adopt tetrahedral structures in the gas phase, and are Lewis acidic. Coordination compounds Complexes of vanadium(II) and (III) are relatively exchange inert and reducing. Those of V(IV) and V(V) are oxidants. The vanadium ion is rather large and some complexes achieve coordination numbers greater than 6, as is the case in [V(CN)7]4−. Oxovanadium(V) also forms 7 coordinate coordination complexes with tetradentate ligands and peroxides and these complexes are used for oxidative brominations and thioether oxidations. The coordination chemistry of V4+ is dominated by the vanadyl center, VO2+, which binds four other ligands strongly and one weakly (the one trans to the vanadyl center). An example is vanadyl acetylacetonate (V(O)(O2C5H7)2). In this complex, the vanadium is 5-coordinate, distorted square pyramidal, meaning that a sixth ligand, such as pyridine, may be attached, though the association constant of this process is small. Many 5-coordinate vanadyl complexes have a trigonal bipyramidal geometry, such as VOCl2(NMe3)2. The coordination chemistry of V5+ is dominated by the relatively stable dioxovanadium coordination complexes which are often formed by aerial oxidation of the vanadium(IV) precursors indicating the stability of the +5 oxidation state and ease of interconversion between the +4 and +5 states. Organometallic compounds Organometallic chemistry of vanadium is well developed. Vanadocene dichloride is a versatile starting reagent and has applications in organic chemistry. Vanadium carbonyl, V(CO)6, is a rare example of a paramagnetic metal carbonyl. Reduction yields V (isoelectronic with Cr(CO)6), which may be further reduced with sodium in liquid ammonia to yield V (isoelectronic with Fe(CO)5). Occurrence Universe The cosmic abundance of vanadium in the universe is 0.0001%, making the element nearly as common as copper or zinc. Vanadium is detected spectroscopically in light from the Sun and sometimes in the light from other stars. Earth's crust Vanadium is the 20th most abundant element in the earth's crust; metallic vanadium is rare in nature (known as native vanadium), but vanadium compounds occur naturally in about 65 different minerals. At the beginning of the 20th century a large deposit of vanadium ore was discovered, the Minas Ragra vanadium mine near Junín, Cerro de Pasco, Peru. For