Rhodium physical properties

Hydride Complexes of Ruthenium, Rhodium, and Iridium G. L. Geoffroy and J. R. Lehman Structures and Physical Properties of Polynuclear Carboxylates Janet Catterick and Peter Thornton... 

Rhodium is a hard shiny-white metal that resists corrosion from oxygen, moisture, and acids at room temperatures. As a member of group 8 (VIII), Rh shares many chemical and physical properties with cobalt (j Co) just above it and iridium ( ylr) below it in the vertical group. Therefore, it is considered one of the elements that are transitory between metals and nonmetals. It is rare and only found in combination with platinum ores. 

Elemental composition Rh 49.17%, Cl 50.83%. Rhodium is analyzed in an aqueous solution (or after dissolving in water) by AA or other techniques. Insoluble chloride is extracted with aqua regia, diluted, and analyzed to determine the rhodium content using various instrumental techniques. The chloride may be decomposed at elevated temperatures and liberated chlorine identified by color and other physical properties. Chlorine may be measured quantitatively by dissolving in an acidified solution of potassium iodide and titrating liberated iodine with a standard solution of sodium thiosulfate, using starch indicator. 

Elemental composition (Rh203) Rh 81.09%, 0 18.91%. The oxide may be solubilized by treatment with alkali to form hydrated oxide, which may be dissolved in acid and diluted for analysis of rhodium metal by AA or ICP. The oxide may be characterized by x-ray diffraction, physical properties, and reaction with strong alkali to form yellow precipitate of pentahydrate, and in excess alkali a black precipitate of the trihydrate. 

In this type of complex rhodium(I) achieves its maximum coordination number with neutral ligands. As might be expected, very few complexes of this type are known. The isolable examples are unstable and easily lose neutral ligands. The complexes so far isolated contain five trialkyl phosphite ligands. These ligands have high jr-acidity but are poor acetone solution. Their physical properties are shown in Table 14. 

There remain a number of other five-coordinate complexes whose physical properties are shown in Table 66. Of these complexes only the AsCy3 complex has been prepared from a rhodium(III) source (equation 194). The remainder have been prepared from oxidative addition reactions of [RhCl(PPh3)3], The arylazo complexes have structure (75),948 whilst the sulfinato complexes are bound through sulfur.950... 

These complexes are produced when rhodium trichloride is allowed to react with two, or less, equivalents of tertiary phosphine or arsine (equation 199). Their physical properties are listed in Table 68, and the complexes have been shown to adopt the non-centrosymmetric structure (80).977 This is in agreement with the dipole moment972 and 3IP NMR spectrum978 of the tributylphosphine... 

The complexes have been prepared by several methods. When ethanolic KOH and rhodium Table 69 Physical Properties of a-[RhHX, L3] Complexes... 

One interesting reaction undergone by the tri(styryl)arsine complexes is the bromination of the C=C bond by bromine in CC14 (equation 217).1013 Similar behavior970 is exhibited by the few tertiary stibine complexes (Table 75) that have been isolated. Few physical properties of these complexes have been investigated, but the 121 Sb Mossbauer parameters for both rhodium(III) complexes and the free ligands have been determined.1016... 

There are two monohydrido complexes which have been prepared by the oxidative addition of hydrogen halides to [Rh P(OMe)3 5][BPh4] (equation 223). Two other monohydrido complexes having hydrogen-bonded anions have been prepared by simultaneous substitution of and oxidative addition to dinuclear rhodium(I) complexes (equation 224). The anions give resonances at very low fields in the H NMR spectra of the complexes.1050 The physical properties of the monohydrido complexes are listed in Table 77. 

The other hydrogen halides add oxidatively to rhodium(I) complexes of ditertiary phosphines or arsines giving rise to numerous monohydrido complexes, whose physical properties are also listed in Table 79. However, it is possible to prepare certain monohydrido complexes from rhodium(III) halides. One interesting reaction, carried out under an atmosphere of CO, gives rise to dicar-bonyldichlororhodate(I) salts (equation 241).226... 

Tetrafluoroborate,223 tetraphenylborate and iodide227 salts of a large range of rhodium(I) complex cations react oxidatively with dioxygen (equation 242). The physical properties of the dioxygen complexes are given in Table 80. The claim that a rhodium(I) species containing a ditertiary arsine... 

Table 80 Physical Properties of Dioxygen, Disulfur and Diselenium Rhodium(III) Complexes containing...

Since, in the main, complexes of this type are themselves derivatives of other rhodium complexes there seem to have been few investigations of their chemical reactions apart from the metathetical reactions outlined above. Apart from spectral studies there has been little interest shown in their physical properties, although it may be noted that the emission observed from [RhCl2 ((Ph2Z)2C2H4 2]Cl (Z = P, As) complexes has been attributed to metal-localized phosphorescence.1 43 The ditertiary phosphine complexes are listed in Table 81. 

Tertiary phosphine analogs have been prepared from [Rh(NO)2Cl]x.1301 Nitrosyltris(phosphorus trifluoride)rhodium has been prepared from both rhodium(—I) and rhodium(I) complexes (equations 294-296).1297 Their physical properties are listed in Table 90. The triphenylphosphine complex is quite reactive (Scheme 42). Both electronic1312 and 31P NMR spectrometry show the equilibrium constant for the reaction (297) to be of the order of 10-4moldm3 in dichloromethane, benzene1312,1313 or THF,1313 so the reactivity of the complex cannot arise from the facile loss of a... 

Probably the most numerous bimetallic complexes of rhodium are those containing mercury. The complex //-[RhHCl (AsMePh,)3 ] reacts with mercury(II) halides,1351 phenylmercury(II) halides,1352 or mercury(I) halides 351,1352 to produce/ac-rhodium-mercury complexes (145) (equation 333). The physical properties of the products are shown in Table 94. 

Table 94 Physical Properties of Rhodium-Mercury Compounds...

Modem values for its physical properties are the more reliable since rhodium is difficult to obtain in a highly pure state because of reactions with refractory containers at or near its melting point. The purest samples have been obtained by zone refining. The differing standards of purity can be seen in the range of boiling points (3700-4500 °C) quoted. 

The chemical nature and composition of nitric acid were first determined in 1784 by the English chemist and physicist Henry Cavendish (1731-1810). Cavendish applied an electric spark to moist air and found that a new compound-nitric acid-was formed. Cavendish was later able to determine the acid s chemical and physical properties and its chemical composition. The method of preparation most commonly used for nitric acid today was one invented in 1901 by the Russian-born German chemist Friedrich Wilhelm Ostwald (1853-1932). The Ostwald process involves the oxidation of ammonia over a catalyst of platinum or a platinum-rhodium mixture. 

PHYSICAL PROPERTIES Physical appearance and odor vary depending upon the specific soluble rhodium compound, (hydrated rhodium trichloride) deep-red, hygroscopic crystals odorless solid or liquid very soluble in water soluble in hot ethanol MP (100°C, 212°F) (decomposes) BP (800°C, l472°F)(sublimes) DN/SG (>1) VD (NA) VP (<0.1 mmHg at 20°C). 

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