Oxides trihalides

Niobium pentaoxide undergoes two important types of reactions, one is reduction to niobium metal or to lower oxides, and the other involves conversion of pentoxide to oxide trihalides when treated with halogens or hahdes. These reactions occur mostly at elevated temperatures. Reductions may he carried out hy carhon, hydrogen, niobium carbide, niobium metal, and other reducing agents at elevated temperatures and often in vacuum ... 

The oxide trihalides are monomeric in the vapor state but the lower volatility, compared to that of the corresponding pentahalides, is understandable in view of the structure of NbOCI3 (Fig. 26-B-4). 

Pyridazines form complexes with iodine, iodine monochloride, bromine, nickel(II) ethyl xanthate, iron carbonyls, iron carbonyl and triphenylphosphine, boron trihalides, silver salts, mercury(I) salts, iridium and ruthenium salts, chromium carbonyl and transition metals, and pentammine complexes of osmium(II) and osmium(III) (79ACS(A)125). Pyridazine N- oxide and its methyl and phenyl substituted derivatives form copper complexes (78TL1979). 

Lower oxidation states are rather sparsely represented for Zr and Hf. Even for Ti they are readily oxidized to +4 but they are undoubtedly well defined and, whatever arguments may be advanced against applying the description to Sc, there is no doubt that Ti is a transition metal . In aqueous solution Ti can be prepared by reduction of Ti, either with Zn and dilute acid or electrolytically, and it exists in dilute acids as the violet, octahedral [Ti(H20)6] + ion (p. 970). Although this is subject to a certain amount of hydrolysis, normal salts such as halides and sulfates can be separated. Zr and are known mainly as the trihalides or their derivatives and have no aqueous chemistry since they reduce water. Table 21.2 (p. 960) gives the oxidation states and stereochemistries found in the complexes of Ti, Zr and Hf along with illustrative examples. (See also pp. 1281-2.)... 

Molybdenum hexafluoride. 3,1412 Molybdenum-iron-sulfur complexes, 4,241 Molybdenum oxide amino acid formation prebiotic systems, 6, 872 Molybdenum storage protein microorganisms, 6, 681 Molybdenum telluride, 3, 1431 Molybdenum tetraalkoxides physical properties, 2, 347 Molybdenum tribromide, 3,1330 Molybdenum trichloride, 3,1330 Molybdenum trifluoride, 3, 1330 Molybdenum trihalides, 3, 1330 bond lengths, 3, 1330 magnetic moments, 3,1330 preparation, 3,1330 properties, 3, 1330 structure, 3,1330 Molybdenum triiodide, 3,1330 Molybdenum trioxide complexes, 3, 1379 Molybdenum triselenide, 3, 143)... 

Exceptions to the rule are observed for compounds with low polarity, i.e. when covalent bonds predominate. Fluorides and oxides (including silicates) usually fulfill the rule, whereas it is inapplicable to chlorides, bromides, iodides, and sulfides. For instance, in metal trifluorides like FeF3 octahedra sharing vertices are present, while in most other trihalides octahedra usually share edges or even faces. 

Rowley, A. T. et al., Inorg. Chem. Acta, 1993, 211(1), 77 Preparation of metal oxides by fusing metal halides with lithium oxide in a sealed tube leads to explosions if halide hydrates are employed, particularly lanthanide trihalide hydrates. The preparation succeeds with anhydrous halides. This will be purely a question of vapour pressure above an exothermic reaction the question is whether the vapour is water, or metal halide, and the reaction oxide formation, or hydration of lithium oxide. Like other alkali metal oxides, hydration is extremely energetic. 

Antimony oxide is known as a flame retardant synergist when used in combination with halogen compounds. Volatile antimony oxyhalide (SbOX) and/or antimony trihalide (SbX3) are formed in the condensed phase and transport the halogen into the gas phase (3). It has been suggested that antimony is also a highly active radical trap (4). 

Elder, R.C., Florian, L.R., Kennedy, E.R., and Macomber, R.S., Phosphorus containing products from the reaction of propargyl alcohols with phosphorus trihalides. II. The crystal and molecular structure of 2-hydroxy-3,5-di-ferf-butyl-l,2-oxaphosphol-3-ene 2-oxide, /. Org. Chem., 38, 4177, 1973. 

Molybdenum supplements, 17 40 Molybdenum trihalides, 17 26 Molybdenum trioxide, 17 9, 20 Molybdenum wire, manufacture of, 17 9 Molybdic oxide, 17 9... 

Before the availability of high-purity lanthanide metals, the most popular starting material was the oxide, readily available pure. Because of their high stability, the oxides cannot readily be converted into the respective trihalides simply by reaction with chlorine or hydrogen chloride as oxochlorides are formed nevertheless, Templeton and Carter (45) have prepared pure trichlorides using this method. 

Trihalides can be produced by heating the oxide with an excess of ammonium halide at a high temperature. The excess ammonium halide is sublimed off in N2, He (12), or in vacuo (39, 77-84). 

The oxides have been converted to the trihalides by reaction with amine hydrohalides with mp <200°C (e.g., PhNH2, MeNH2, Me2NH, EtNH2, Et NH, etc.). A double salt was formed from the reaction with the hydrohalide, which served both as solvent and halogenating agent. The reaction mixture was heated to vaporize the solvent and decompose the double salt, leaving the anhydrous halide (85). 

Rare-earth oxides dissolve in dilute hydrohalic acids to produce solutions of the trihalides which can be crystallized, giving six to nine waters of hydration depending upon the halide (cf. Table I). These hydrates cannot be thermally dehydrated, as oxohalides are formed ... 

The methods discussed produce trihalides of varying purity however, if very pure trihalides are required, they can be sublimed at high temperature from any oxide or oxohalide impurities. The trichlorides can usually be obtained pure, but the tribromides and triiodides tend to be contaminated with oxides and oxoiodides. The various methods of preparing triiodides are compared by a few authors 39, 40, 49, 132), and they recommend their preferred route, which generally is the direct reaction between the metal and iodine. 

Studies of Equilibria and Shift Reagents.—N.m.r. studies of the exchange of halogen in boron trihalide adducts of trimethylphosphine, its oxide, and sulphide,49 and exchange of chloro- and methoxy-groups between methylphosphino and methyl-silyl or -germyl moieties,80 have been reported. The rates of ionization of phosphoranes... 

The most widely studied transition metal is titanium. At various times, all oxidation states of titanium (II, III, IV) have been proposed for the active site of titanium-based initiators. Most of the evidence points to titanium (HI) as the most stereoselective oxidation state, although not necessarily the most active nor the only one [Chien et al., 1982]. (Data for vanadium systems indicate that trivalent vanadium sites are the syndioselective sites [Lehr, 1968].) Initiators based on the a-, y-, and 8-titanium trihalides are much more stereoselective (iso-selective) than those based on the tetrahalide or dihalide. By itself, TiCl2 is inactive as an initiator but is activated by ball milling due to disproportionation to TiCl3 and Ti [Werber et al., 1968]. The overall stereoselectivity is usually a-, y-, 8-TiCl , > TiCL > TiCLj P-TiCl3 [Natta et al., 1957b,c],... 

Metallic samarium is obtained by heating the oxide, Sm203 with lanthanum turnings or cerium in slight excess amounts in a tantalum crucible under high vacuum. The metal is recovered by condensation of its vapors at 300 to 400°C. The metal cannot be obtained by reduction of its halides, SmFs or SmCls, or by heating with calcium or barium. In such reduction, trihalides are reduced to dihalides, but not to the metal. 

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