Trihalides. metal

A complete set of trihalides for arsenic, antimony and bismuth can be prepared by the direct combination of the elements although other methods of preparation can sometimes be used. The vigour of the direct combination reaction for a given metal decreases from fluorine to iodine (except in the case of bismuth which does not react readily with fluorine) and for a given halogen, from arsenic to bismuth. 

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). 

AIF3 is made by treating AI2O3 with HF gas at 700° and the other trihalides are made by the direct exothermic combination of the elements. AIF3 is important in the industrial production of A1 metal (p. 219) and is made on a scale approaching 700000 tonnes per annum world wide. AICI3 finds extensive use as a Friedel-Crafts catalyst (p. 236) its annual production approaches lOOOOOtpa and is dominated by Western Europe, USA and Japan. The price for bulk AICI3 is about 0.35/kg. 

Many of the trihalides of As, Sb and Bi hydrolyse readily but can be handled without great difficulty under anhydrous conditions. AsFs and SbFs are important reagents for converting non-metal chlorides to fluorides. SbFs in particular is valuable for preparing organofluorine compounds (the Swans reaction) ... 

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.)... 

The most stable product of the action of fluorine on metallic palladium is actually Pd [Pd Fg], and true trihalides of Pd do not occur. Similarly, the diamagnetic trichloride and tribromide of Pt... 

All four monohalides of gold have been prepared but the fluoride only by mass spectrometric methods. AuCl and AuBr are formed by heating the trihalides to no more than 150°C and Aul by heating the metal and iodine. At higher temperatures they dissociate into the elements. Aul is a chain polymer which features linear 2-coordinate Au with Au-I 262 pm and the angle Au-I-Au 72°. 

The anhydrous trihalides are ionic, high melting, crystalline substances which, apart from the trifluorides are extremely deliquescent. As can be seen from Table 30.4, the coordination number of the Ln changes with the radii of the ions, from 9 for the trifluorides of the large lanthanides to 6 for the triiodides of the smaller lanthanides. Their chief importance has been as materials from which the pure metals can be prepared. 

For single crystals, the same method is applied, using an excess of metal and of halogen. After reaction, the mixture of the sulfide halide and the halide is heated to a temperature slightly above the melting point of the respective halide. Perfect, small crystals for X-ray determination are formed. The excess of the trihalide is removed by treatment with anhydrous alcohol 92, 93, 96). CeSI may also be prepared from the sulfides 68, 93) CeSCl is formed by reaction 4 92). 

Only some Lewis acid-base adducts of group 13 trialkyls R3M or trihalides CI3M and transition metal complexes of the type LnFe—E=CR2, (E = P, As) Weber L, Scheffer MH, Stammler HG, Stammler A (1999) Eur J Inorg Chem 1607 (LnW=P) Scheer M, Muller J, Baum G, Haser M (1998) J Chem Soc Chem Commun 1051, have been synthesized and structurally characterized... 

Unlike the di-f dihalides, such compounds differ little in energy from both the equivalent quantity of metal and trihalide, and from other combinations with a similar distribution of metal-metal and metal-halide bonding. So the reduced halide chemistry of the five elements shows considerable variety, and thermodynamics is ill-equipped to account for it. All four elements form di-iodides with strong metal-metal interaction, Prl2 occurring in five different crystalline forms. Lanthanum yields Lai, and for La, Ce and Pr there are hahdes M2X5 where X=Br or I. The rich variety of the chemistry of these tri-f compounds is greatly increased by the incorporahon of other elements that occupy interstitial positions in the lanthanide metal clusters [3 b, 21, 22]. 

Boron trihalides are strong Lewis acids that react with a wide collection of Lewis bases. Many adducts form with donor atoms from Group 15 (N, P, As) or Group 16 (O, S). Metal fluorides transfer F ion to BF3 to give tetrafluoroborate salts LiF + BF3 LiBF4 Tetrafluoroborate anion is an important derivative of BF3 because it is nonreactive. With four <7 bonds, [BF4 ] anion has no tendency to coordinate further ligands. Tetrafluoroborate salts are used in synthesis when a bulky inert anion is necessary. 

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. 

Intramolecular adducts have also been used as gallium and indium precursor complexes they are synthesized by the alkylation of the group 13 metal trihalide with an appropriate Grignard reagent,89 as shown Figure 20. 

Because of the reactive covalent bonds to halogen atoms, all of the trihalides of the group VA elements hydrolyze in water. It is found that the rates decrease in the order P > As > Sb > Bi, which agrees with the decrease in covalent bond character that results from the increase in metallic character of the central atoms. Not all of the trihalides react in the same way. The phosphorus trihalides react according to the equation... 

Tables 3.28-3.30 summarize the geometry, binding energies, and NBO/NRT descriptors for a variety of linear triatomic XYZ- species. These include representatives of the p-p-p orbital motif (such as symmetric trihalides [X3-, X = F, Cl, Br] and the mixed chlorofluorides [FFCl-, C1FC1-, FC1F-, I CICI-]) as well as the p-s-p (FHF-) and s-s-s (HLiH-, HJ) orbital motifs. (Examples of transition metal species manifesting the s-d-s and p-d-p motifs will be considered in Section 4.10.)...

Undoubtedly, the best method for the production of pure anhydrous lanthanide trihalides involves direct reaction of the elements. However, suitable reaction vessels, of molybdenum, tungsten, or tantalum, have to be employed silica containers result in oxohalides (27). Trichlorides have been produced by reacting metal with chlorine (28), methyl chloride (28), or hydrogen chloride (28-31). Of the tribromides, only that of scandium has been prepared by direct reaction with bromine (32). The triiodides have been prepared by reacting the metal with iodine (27, 29, 31, 33-41) or with ammonium iodide (42). 

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. 

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