Rhodium III

The first step in the reaction of [Co(NH3)5(py)] with hydroxyl radicals is proposed to be attack at the coordinated pyridine. The absorption spectrum of the [Co(NH3)5(pyOH)] radical complex thus produced is given. This intermediate then undergoes redox decomposition. The intermediacy of such a radical complex in the present system is supported by earlier suggestions of the existence of the species [Co(NH3)5(O2C0] and of this or related species during permanganate oxidation of the formate complex [Co(NH3)5(02CH)].  

Although there are many fewer references dealing with kinetics and mechanisms of substitution at rhodium(III), there has been enough activity in the 

Substitution Reactions of Inert Metal Complexes—6 and Above 

The volume of activation for aquation of [Rh(NH3)5(N03)] is -6.9 cm mol This negative value is consistent with a predominantly associative mechanism.Activation parameters for acid aquation of the ci5-[Rh(en)2Cl2] cation are Ea = 23 kcal mol and AS = H-9.6 ( 5.3) cal deg mol . These values were derived from the temperature dependence of rate constants over the range 298-333 

Activation volumes for base hydrolysis in aqueous solution at 313.2 K and an ionic strength of 1.0 mol dm of the complexes [Rh(NH3)sX], with X = Cl, Br, 1, and NO3, are +19.3, +20.2, +20.4, and +22.3 cm mol , respectively. These results, obtained over a pressure range of 1.5 kbar, can be accommodated within the framework of an 5n1CR mechanism. 

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Synthesis. The most important starting material for rhodium compounds is rhodium(III) chloride hydrate [20765-98-4], RhCl3 nH2 O. Other commercially available starting materials useful for laboratory-scale synthesis include [Rh2(0000113)4] [5503-41 -3], [Rh(NH3)201]0l2 [13820-95-6], [Rh20l2(0O)4] [32408-34-7], and [Rh20l2(cod)2] [12092-47-6]. 

Kinetic mles of oxidation of MDASA and TPASA by periodate ions in the weak-acidic medium at the presence of mthenium (VI), iridium (IV), rhodium (III) and their mixtures are investigated by spectrophotometric method. The influence of high temperature treatment with mineral acids of catalysts, concentration of reactants, interfering ions, temperature and ionic strength of solutions on the rate of reactions was investigated. Optimal conditions of indicator reactions, rate constants and energy of activation for arylamine oxidation reactions at the presence of individual catalysts are determined. 

Significant distinction in rate constants of MDASA and TPASA oxidation reactions by periodate ions at the presence of individual catalysts allow to use them for differential determination of platinum metals in complex mixtures. The range of concentration rations iridium (IV) rhodium (III) is determined where sinergetic effect of concentration of one catalyst on the rate of oxidation MDASA and TPASA by periodate ions at the presence of another is not observed. Optimal conditions of iridium (IV) and rhodium (III) determination are established at theirs simultaneous presence. Indicative oxidation reactions of MDASA and TPASA are applied to differential determination of iridium (IV) and rhodium (III) in artificial mixtures and a complex industrial sample by the method of the proportional equations. 

Rhodium (III) chloride [10049-07-7] M 209.3, m >100°(dec), b 717°. Probable impurities are KCl and HCl. Wash solid well with small volumes of H2O to remove excess KCl and KOH and dissolve in the minimum volume of cone HCl. Evaporate to dryness on a steam bath to give wine-red coloured RhCl3.3H20. Leave on the steam bath until odour of HCl is lost - do not try to dry further as it begins to decompose above 100° to the oxide and HCL. It is not soluble in H2O but soluble in alkalis or CN solns and forms double salts with alkali chlorides. [Inorg Synth 7 214 1063.]... 

The submitters used rhodium(III) oxide available from Fluka A G without further purification. The checkers obtained rhodium(III) oxide from Alfa Inorganics. 

In addition to rhodium(III) oxide, cobalt(II) acetylacetonate or dicobalt octacarbonyl has been used by the submitters as catalyst precursors for the hydroformylation of cyclohexene. The results are given in Table I. 

There is also clear evidence of a change from predominantly class-a to class-b metal charactristics (p. 909) in passing down this group. Whereas cobalt(III) forms few complexes with the heavier donor atoms of Groups 15 and 16, rhodium(III), and more especially iridium (III), coordinate readily with P-, As- and S-donor ligands. Compounds with Se- and even Te- are also known. Thus infrared. X-ray and nmr studies show that, in complexes such as [Co(NH3)4(NCS)2]" ", the NCS acts as an A -donor ligand, whereas in [M(SCN)6] (M = Rh, Ir) it is an 5-donor. Likewise in the hexahalogeno complex anions, [MX ] ", cobalt forms only that with fluoride, whereas rhodium forms them with all the halides except iodide, and iridium forms them with all except fluoride. 

A 500-ml rcund-bottom flask is equipped with a reflux condenser, a gas inlet tube, and a gas outlet leading to a bubbler. The flask is charged with a solution of rhodium (III) chloride trihydrate (2 g) in 70 ml of 95 % ethanol. A solution of triphenylphosphine (12 g, freshly recrystallized from ethanol to remove the oxide) in 350 ml of hot ethanol is added to the flask, and the system is flushed with nitrogen. The mixture is refluxed for 2 hours, following which the hot solution is filtered by suction to obtain the product. The crystalline residue is washed with several small portions of anhydrous ether (50 ml total) affording the deep red crystalline product in about 85% yield. 

Rhodium(III) hydroxide is an ill-defined compound Rh(0H)3.nH20 (n 3) obtained as a yellow precipitate by careful addition of alkali to Na3RhCl6-Addition of imidazole solution to suitable aqua ions leads to the precipitation of active rhodium(III) hydroxides formulated as Rh(0H)3(H20)3, Rh2(/x-0H)2(0H)4(H20)4 and Rh3(/z-0H)4(0H)5(H20)5 [31]. Hydrated iridium(III) hydroxide is obtained as a yellow precipitate from Ir3+ (aq.) at pH 8. 

The reaction with Mel proceeds in two stages. Initial reaction is oxidative addition to give a rhodium(III) species, isolated as a Mel adduct... 

Like other planar rhodium(I) complexes, Rh(RNC)4 undergoes oxidative addition with halogens to form 18-electron rhodium(III) species and also add other small molecules (S02, NO+) (Figure 2.31). 

ESCA data support a rhodium(II) oxidation state in these compounds. Therefore, the Rh 3d5//2 binding energy is c. 309.2 eV in simple car-boxylates, midway between those in typical rhodium(I) complexes (c. 308.5 eV) and rhodium(III) complexes (c. 310.7 eV) [72],... 

Photolysis of the rhodium(III) complex of octaethylporphyrin gives a rhodium(II) dimer that readily undergoes addition reactions to afford rhodium(III) species (Figure 2.42). 

A considerable number of rhodium(III) complexes exist. Their stability and inertness are as expected for a low-spin d6 ion any substitution leads to a considerable loss of ligand-field stabilization. 

Amine complexes are an important class of rhodium(III) complex. Figure 2.44 shows some relationships. 

Figure 2.44 Syntheses and reactions of rhodium(III) ammine complexes.

Figure 2.47 The limiting photosubstitution mechanism for rhodium(III) ammine complexes. (Reprinted from Coord. Chem. Rev., 94, 151, 1989, with kind permission from Elsevier Science S.A., P.O. Box 564, 1001 Lausanne, Switzerland.)...

Apart from ethanol, other primary alcohols catalyse the formation of the dichloro complex, probably via a rhodium(I) intermediate rather than a rhodium(III) hydride. Rhpy4X2" compounds have anti-bacterial activity. 

Thiacrown ether and related systems also tend to involve octahedrally coordinated rhodium(III) [107]. 

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