Potassium hexachlororhodate

The solvents are laboratory grade. Methanol and chloroform are distilled and stored under nitrogen before use. Sodium-dried tetrahydrofuran (THF) is redistilled over LiAlH4 under nitrogen before use. ( Caution. To minimize the chance of explosion, peroxide-free THF must be employed. See Reference 8 for details.) The aqueous solutions are carefully degassed in vacuo and saturated with nitrogen before use. Potassium hexachlororhodate(3-) monohydrate is prepared as described in the literature.4 The operations are carried out with the usual Schlenk apparatus.5... 

Nitrosylpentaamminecobalt(II) chloride, synthesis 49 cts-Bromoamminebis (ethylenediamine) cobal t (111) bromide, CIS- and trans-aquoamminebis(ethylenediamine)cobalt(IIl) bromide, and cis- and triphenylphosphine)rhodium and chloro-carbonylbis(triphenylarsine)rhodium, synthesis 56 Sodium hexachlororhodate(III) 2-hydrate and potassium hexachlororhodate(III) 1-hydrate, synthesis 57 Ammonium hexachloroiridate(IV), synthesis 58 Resolution of the tris(l,10-phenanthroline)nickel(II) ion, synthesis 59... 

SODIUM HEXACHLORORHODATE(m) 2-HYDRATE AND POTASSIUM HEXACHLORORHODATE(m) 1-HYDRATE... 

Potassium hexachlororhodate(III) 1-hydrate may be obtained by chlorination of a mixture of powdered rhodium and potassium chloride, followed by crystallization from the reaction mixture solution in the presence of excess potassium chloride. It may also be prepared by reaction of sodium hexachlororhodate(III) solution with concentrated potassium chloride solution, followed by evaporation to incipient crystallization. Both of these methods are reported to yield potassium pentachloroaquorhodate(III) if potassium chloride is not present in excess. - Anhydrous potassium hexachlororhodate(III) is obtained by heating potassium hexachlororhodate(III) 1-hydrate at 100 to 120°. ... 

Ten milliliters of water is added to the filtrate (p. 220), followed by slow addition, with stirring, of 18 ml. of 25% potassium chloride solution. On cooling for 30 minutes in an ice bath, dark burgundy-colored crystals form. These crystals are collected on a fritted-glass filter and washed with 60% ethanol (about 75 ml.) until free of chloride ion.J The product is washed further with 25 ml. of 95% ethanol and then with two 50-ml. portions of diethyl ether. Upon air drying, 4.10 to 4.30 g. of potassium hexachlororhodate-(III) 1-hydrate is obtained (91 to 95% yield). Anal. Calcd. 

A solution of the potassium salt is prepared in exactly the same way as that of the sodirnn salt. On concentration, the first crystallization yields K3[RhCl5(HsO)]. This salt is dissolved in an almost saturated aqueous KCl solution and the solution concentrated the hexachlororhodate KaRhCla HgO crystallizes out on cooling. Both of the above compounds form dark-red crystals. 

The solution is concentrated to 20 ml. on a steam bath and then cooled to about 0 to 5°. Hydrogen chloride gas (e.g., from a HC1/H S04 generator) is slowly bubbled for 30 minutes through the concentrated burgundy-colored solution in an ice bath. The solution turns a dark burgundy-purple and contains hexachlororhodic(III) acid. The precipitated sodium chloride is removed by filtration with a coarse sintered-glass funnel and washed with cold concentrated (12 N) hydrochloric acid (5 to 8 ml.). An almost quantitative recovery (3.45 to 3.50 g.) of sodium chloride is obtained. At this stage, either the sodium salt (Procedure A) or the potassium salt (Procedure B) of the hexachlororhodate(III) anion may be isolated from the filtrate. 

---