Pentachloride oxidation states

Chlorine reacts with most elements, both metals and non-metals except carbon, oxygen and nitrogen, forming chlorides. Sometimes the reaction is catalysed by a trace of water (such as in the case of copper and zinc). If the element attacked exhibits several oxidation states, chlorine, like fluorine, forms compounds of high oxidation state, for example iron forms iron(III) chloride and tin forms tin(IV) chloride. Phosphorus, however, forms first the trichloride, PCI3, and (if excess chlorine is present) the pentachloride PCI5. 

Molybdenum metalworking, 17 10-11 Molybdenum mill products, 17 9-10 Molybdenum-nickel alloys, 17 102 Molybdenum ore, U.S. exports of, 17 3t Molybdenum oxidation states, 17 20 Molybdenum oxides, 17 38 Molybdenum pentachloride, 17 23 Molybdenum-rhenium alloys, 17 15 Molybdenum sulfide, poisons in representative reactions, 5 258t Molybdenum-sulfur complexes, molecular, 17 37... 

There is a definite tendency for the nonmetals of the fourth row—As. Se, and Br—to be unstable in their maximum oxidation state. For example, the synthesis of arsenic pentachloride eluded chemists until comparatively recently, v although both PCI, and SbCI, are stable. The only stable arsenic pentahalide is AsFs AsCU decomposes at -50 °C, and AsBrs and Asl5 are still unknown. 

Group-5 elements are most stable in their maximum oxidation state +5 and therefore form pentahalides, see Figure 7. Most volatile are the pentafluorides, followed by the pentachlorides and the pentabromides. Besides the pure halides, also the oxyhalides (MOX3) are stable in the gas phase. They should be less volatile compared to the pure halides. This was confirmed experimentally for niobium, see Figure 8. 

Element 106. The chemical properties of element 106 (eka-tungsten) are predicted to be similar to those of tungsten, molybdenum and to some extent chromium, offering an even richer chemistry of complex ions than these elements. The hexafluoride should be quite volatile and the hexachloride, pentachloride and oxychloride should be moderately volatile. Penneman and Mann predict a -)-4 oxidation state in aqueous solution. Jprgensen s selection of k is for the hydrated cation and is not intended to account for the effects of complex ion formation. However, since tungsten is stabilized in the oxidation state of -t-6 by the tungstate ion, an analogous situation may be expected for element 106. 

Both phosphorus trichloride and phosphorus pentachloride react with water in a hydrolysis reaction, a reaction with water in which new element-oxygen bonds are formed and there is no change in oxidation state. An oxoacid and hydrogen chloride gas are formed in the reaction. 

With an excess of chlorine, the product is phosphorus pentachloride, which contains phosphorus in the +5 oxidation state ... 

Tantalum is a gray, very hard, malleable, and ductile metal, with an atomic mass of 180.95 and atomic number 73 (Merck Index Online 2002). The boiling point of 5429°C and a melting point of 2996 °C are exceeded only by those of rhenium and tungsten (Hammond 1986, Merck Index Online 2002). Numerous forms of tantalum exist, including pentachloride, pentafluoride, and pent-oxide salts, which are insoluble in water. The most stable oxidation state is + 5. Tantalum is almost twice as dense as iron (density 16.6 gcm ) and about 90% as stiff, with a modulus of elasticity value, E = 2.7x10 psi (Taylor 1969, Merck Index Online 2002). 

Element A. when heated in air, formed a volatile oxide containing A in its highest oxidation state. On treatment with chlorine A formed a pentachloride as a dark-red solid which, in its simplest structural unit, contained two hexaco-ordinated atoms of A. Fluorides of A in two higher oxidation states are also known. 

Information on the carbonyl chemistry of niobium and tantalum is, to date, very meager. The main difficulty appears to be the reduction of the usual pentavalent derivatives of these metals to the very low formal oxidation states of metal carbonyl derivatives. Nevertheless, the yellow anions [M(C0)6] (M = Nb, Ta) have been obtained by a method analogous to, but more difficult than, one of the preparations of the [VCCO) ]" anion. The method involves reduction of the pentachlorides with sodium metal in diglyme in the presence of high pressures of carbon monoxide (63). The niobium and tantalum derivatives are much more air-sensitive than the analogous vanadium derivative. The niobium derivative has not yet been obtained analytically pure (63). No chemistry of the [Nb(CO)J and the [Ta(CO)6] ions has been reported, even conversion to the neutral carbonyl derivatives [M(CO) (M = Nb or Ta = 1 or 2) or to the carbonyl hydride derivatives HM(CO)6 (M = Nb, Ta) still presenting unsolved problems. 

The decreasing stabUity of the +5 oxidation state is shown by the fact that all 16 EX3 compounds (E = P, As, Sb, Bi X = F, Cl, Br, I) are formed, but only phosphorus forms pentahalides with all four halogens. Arsenic and antimony form only the pentafluoride and pentachloride, whereas bismuth forms only the pentafluoride. Of the pentafluorides of the lower three pnicogens, only ASF5 is trigonal bipyrami-dal. SbFj and BiFj are polymers of EF octahedra held together by bridging fluorine atoms. 

In the present work we conducted spectroscopic studies of anodic dissolution of metallic niobium, dissolution of niobium pentachloride and chlorination of various niobium oxides (NbO, Nb02, Nb205) by HCl in LiCl-KCl and NaCl-CsCl eutectics and NaCl-KCl equimolar melts at 450-750 °C. In a separate series of experiments the speciation of niobium was studied using spectroelectrochemistry and exchange reactions between niobium metal and bismuth, silver or nickel ions in NaCl-KCl-based melts. Oxidimetric titration [9] was employed to determine an average oxidation state of niobium in melt samples rapidly quenched under inert conditions. 

The dissolution of niobium pentachloride in molten alkali chlorides was studied in NaCl-KCl-, NaCl-CsCl-and LiCl-KCl-based melts and the progress of the dissolution was followed by in situ spectroscopy measurements. In most instances the spectra contained only the low energy edge of the charge transfer band. The oxidation state of niobium in quenched melt samples of the obtained electrolytes was close to 5.0 (Table 4.4.1). This result is in a good agreement with the literature data [2-6] and indicates that NbClg" species constituted the main product of this reaction. 

Niobium Pentafluoride, NbFs, is the only known compound of niobium and fluorine, and even this cannot be obtained in the free state by a wet method because of the extreme readiness with which it hydrolyses. Niobium pentoxide dissolves readily in hydrofluoric acid, but evaporation of the solution leaves a residue of the unchanged oxide. Niobium pentafluoride has been prepared synthetically 1 by passing dry fluorine over the gently heated metal contained in a boat in a platinum tube. The product is freed from platinum tetrafluoride, a little of which is formed at the same time, by distillation in vacuo at 100° to 110° . An alternative method consists in treating niobium pentachloride with anhydrous hydrogen fluoride in a freezing mixture and purifying by redistillation.3... 

Acetyl mandelic acid was described by Naquet and Lougui-nine,1 but their product has been shown to be contaminated with the ethyl ester of acetyl mandelic acid. Dupont2 obtained the compound by the oxidation of diacetyl 1, 4-diphenylbutine-2-diol-i, 4. Anschutz and Bocker3 prepared acetyl mandelic acid, and from it the acid chloride, by the use of phosphorus pentachloride, but with poor yields. Von Braun and Muller 4 state that acetyl mandelyl chloride can be made from acetylated mandelic acid and thionyl chloride, the resulting product being a viscous yellow oil. 

---