Oxyhalides Oxychlorides

Many lanthanide oxyhalides, MOCl (M=La—Ho), MoBr (M= lanthanides and Y) and MOI (M = La, Sm, Eu, Tm, Yb) crystallize in tetragonal PbFCl structure type [98, 137—141). However, the heavier lanthanide oxychlorides (Tm, Yb, Lu) do not crystallize in the PbFCl structure [137) probably because of the short chlorine-chlorine contacts. In the case of the oxybromides, this perturbing effect does not exist and tbe PbFCl structure is preserved through the lanthanide series and including YOBr [139). 

In these oxyhalide complexes, the inter-halide distances between layers are smaller than the sum of the ionic radii of the halides (Table 11). In the oxybromides and ox5dodide series the M—Br (next layer) and M—I (next layer) distances increase (Table 11) with increase in parameter c (Table 10) as these distances depend solely on the dimensions of the c-axis. In the oxychloride series the M—Cl (next layer) distance, however, show a decrease along the lanthanide series. So does the parameter c (Table 10). This is the reason why the oxychlorides of Tm, Yb and Lu cannot maintain the PbFCl type structure. 

Halides and Oxyhalides op Sulphur —Fluorides, Chlorides, Sulphur Bromide, Sulphur and lodino, Oxyfluorides, Oxychlorides, Thionyl Bromide. 

The contaminants in commercial boron trichloride usually are HCI and COCI2, as well as oxychlorides which have some volatility. The oxyhalides are readily removed by one or two trap-to-trap distillations in a clean vacuum system. Most of the HCl can be removed by holding the BCI3 at — 78°C and pumping away the volatiles for a brief period (some BCI3 is sacrificed in the process). Phosgene, which may be detected by its gas-phase infrared absorption at 850 cm"1, is very difficult to remove. Liquid boron tribromide is generally supplied in sealed ampules. If it is straw colored, dibromine is a likely impurity, and this... 

In reporting a Ziegler-Natta catalyst, the kind of transition metal compound should not be omitted. Group 4-8 transition metal compounds, such as halides, oxyhalides, alkoxides, acetylacetonates, etc., have been used as catalyst precursors with activators such as alkyl derivatives or hydrides of group 1-4 metals. Titanium chlorides and triethylaluminium are most commonly applied for the preparation of heterogeneous catalysts in an aliphatic hydrocarbon medium. Also, vanadium oxychloride or acetylacetonate and dialkyaluminium chloride are often used for the preparation of homogeneous catalysts in an aliphatic hydrocarbon or an aromatic hydrocarbon medium. 

In principle, in oxygen containing carrier gases also oxyhalides can be synthesized. However, for group-4 elements little is know about these compounds. It was observed that ZrOCl2 and HfOCl2 decompose to tetrachlorides and the oxide under elevated temperatures [6]. An alternative process is substitutive adsorption of the pure halides on the surface of the quartz chromatography column where oxychloride formation is possible in the adsorbed state only. 

Early on, separation procedures to chemically isolate Sg concentrated on inorganic gas chromatography of chlorides and/or oxychlorides [36]. In a number of studies the gas chromatographic behavior of halide and oxyhalide species of Mo and W were investigated with respect to a physico-chemical characterization of Sg [37 -5]. 

The pentoxide also gives the oxychloride when heated with the halides of other non-metals, although the other non-metal does not necessarily give oxyhalide also. Thus with boron trichloride... 

Numerous 1 1, 1 2, and 1 3 neutral adducts are known for NbOCb. While complexes with N-donors such as amines, nitriles, or with phosphines derive mostly from direct reaction between oxyhalides and the ligands, many MOX3L2 complexes have been obtained by oxygen abstraction from O-donors by pentahalides. This reactivity can be exploited for an easy entry into oxychloride chemistry via the Labile NbOCl3(MeCN)2 complex (1) (equation 3). ... 

All the elements Al, Ga, La, Ti, V, and the 4f and 5f metals form an oxychloride MOCl and most of them also form MOBr and MOI. Antimony and bismuth also form more complex oxyhalides, which are described in Chapter 20, and Bi forms BiOF which belongs in this group. Other oxyfluorides MOF of the above elements were included in group (a), ionic oxyfluorides. 

Other oxyhalides, mostly oxychlorides and oxybromides, result from the controlled hydrolysis of the trihalides, and are of interest for two main reasons. First, they are quite unrelated to the oxyhalides of bismuth. Although both antimony and bismuth form compounds MOX the structures of the antimony compounds are quite different from those of the compounds BiOX, which have been described on p. 408. The more complex oxyhalides of Sb have no analogues among Bi compounds. Second, a feature of the published structures of the antimony oxyhalides is the coordination of Sb by either three or four O atoms. It should perhaps be remarked here that the investigation of the structures of these complex compounds is difficult, and the precise positions of the O atoms are by no means certain. However, it appears that a feature of these compounds is the formation of extended Sb—O systems, generally layers, interleaved with halogen... 

Bismuth oxychloride (BiOCl) is a colorless fine powder, which melts at 232°C and boils at 447°C. It is practically insoluble in water and alcohols, but readily soluble in hydrochloric acid and nitric acid. Above 570°C, it liberates BiCb to be transformed into a Bi405Cl3 compound. Among bismuth oxyha-lides, only the oxychloride is available commercially at a cost of US 30.00 ( 7500) for a sample of 99% purity and US 98.60 ( 24 400) for a sample of 99.99% purity per 50 g. However, other oxyhalides can readily be prepared by partial hydrolysis of trivalent bismuth halides or by the interaction of basic bismuth nitrate (BiO(N03)) with the corresponding sodium halide in aqueous... 

Compared to the case of the dissolution of the halides, the increased complexity of the hydrolysis phenomena and the appearance of small amounts of Th(OH)4(am) precipitate in the case of the dissolution of the oxychloride and the oxybiomide do not permit us to treat the data on the three oxyhalides with sufficient accuracy for any values to be selected. 

Volatility studies of various volatile halides, oxyhalides and/or oxides has been the subject of an extensive experimental research fi om 1969 on when Zvara et al. performed first experiments with RfCU [45,196-198]. Since then, volatility studies were performed for group-4 and -5 chlorides, bromides and oxychlorides, group-6 and -7 oxychlorides and group-8 oxides. The experiments have established a number of trends in volatilities of the heaviest element compounds, while they have also revealed a number of controversies. Results of... 

Several studies of the effect of pressure on the radial Bkq crystal field parameters have been reported. Lanthanide oxyhalides (REOX RE = La, Gd, Y X = Cl, Br) doped with Eu + have been extensively studied. The REOX lattices are iso-structural and incorporate Eu + in bonding sites with 4 symmetry. In the oxybromides, Eu " is coordinated to four oxygens and four bromides. The RE-0 bond lengths ( 2.3 - 2.4 A) are significantly shorter than the RE-Br bond lengths ( 3.2-3.3 A). A fifth, more distant bromide ( 3.5-3.9 A) is located on the C4 axis [191]. Eu + in the oxychlorides is coordinated similarly (RE-0 2.3-2.4 A, RE-Cl 3.0-3.2 A), but differs with respect to the position of the fifth chloride. The smaller size of the chlorides allows the fifth, axial chloride to approach more closely Eu " and enter the coordination sphere at a distance of 3.0 - 3.2 A [ 192]. 

According to the different donor properties found in this group of solvents a distinction may be made between (a) oxyhalides with low donor numbers including carbonyl chloride, nitrosyl chloride, thionyl chloride, sulphuryl chloride, acetyl and benzoyl halides and (b) oxyhalides with medium donor numbers, namely phosphorus oxychloride, selenium oxychloride and phenyl phosphonic halides, the latter having donor properties approaching those of water or of the ethers. 

In the oxyhalides discussed so far the donor properties at the 0-atoms are too small to be considered in connection with the formation of anionic complexes and their capacities for solute-dissolution are poor. Solvents of higher donor number allow a wider range of solubilities, since more energy is provided by the interactions with acceptors, such as metal ions. Selenium oxychloride , phosphorus oxychloride and phenylphosphonic dichloride are much better donor-solvents than the oxyhalides discussed above. Coordination chemistry in their solutions may be explained in terms of competing reactions between the donor solvent molecules and the competitive ligands towards the acceptor molecules or acceptor ions ... 

Groeneveld s has suggested that coordination occurs through the oxygen atom of the oxyhalide, and this has been confirmed by the results of X-ray work on solvates of phosphorus oxychloride " 5 notably by Lindqvist and his coworkers, e. g. ... 

The same conclusions were drawn from infrared and Raman work ". Data on the chloride ion donor strength of the oxyhalide solvents is, however, not available. One of the main difficulties is the removal of the last traces of water and its elimination during the reactions. Although experimental methods have been considerably improved, it must be born in mind that apparently nobody has ever been successful in working in the complete absence of moisture or of hydrolysis products. Traces of water appear to remain even in reactive liquids, such as the oxychlorides under consideration. It seems that in phosphorus oxychloride small amounts of water form HaO+Cl" which is dissociated in the solution and contrasts with the behaviour of anhydrous hydrogen chloride when dissolved in the same solvent. Thus purified phosphorus oxychloride contains approximately moles of water per liter and this must be taken into consideration, when the pure solvent or when dilute solutions are considered. The assumption of the seK-ion-ization equilibria in the liquid sol vents, 79... 

Potentiometric and spectrophotometric methods have been used to obtain information about the extent of chloride ion transfer with the formation of chloronium ions and thus about the chloride ion donor strength of metal chlorides in different oxyhalides solvents. The chloride ion donor properties are increased by a solvent of high donor number and decreased by a weak donor solvent, if the chloronium ions are solvated. Thus the chloride ion donor strength of a particular chloride is higher in phenylphosphonic dichloride than in phosphorus oxychloride and is usually non-apparent in benzoyl chloride ... 

Various colour indicators may be used in oxyhalide systemsi i ii ii. Sulphon-phthalein indicators were investigated in phosphorus oxychloride i , thionyl chloride and acetyl chloride . The colour changes occurring reversibly at certain pci-values are independent both from the nature of the solvent and from the nature of the solutes changing the chloride ion activity of the solution. The solutions are slightly yellow in media of high chloride ion activity and red in solutions of low chloride ion activities. Red solutions are also formed in highly acidic aqueous solutions. 

Palladium complexes with an heterocyclic N-containing ligand have been used in the carbonylation of aromatic nitro compounds with cocatalysts such as cyclopentadienyl halides or oxyhalides of transition metals belonging to group V e.g. CP2VCI) [168], a cyclopentadienyl halide or oxyhalide together with phosphorus oxytrichloride [169], or a 1,3-diketone derivative of vanadium [170], even also in the presenee of phosphorus oxychloride [171]. 

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