Hexacyanochromate

Potassium hexacyanochromate (III) (BHjO) [ 13601-11 -1 ] M 418.5. Crystd from water. 

Fig. 8. The water-proton spin-lattice relaxation rates vs. magnetic field strength plotted as the Larmor frequency at 282 K for hexacyanochromate(II) ion ( ), trioxalatochromate(III) ion ( ), and trimalonatochromate(III) ion (A). The lines were computed using translational diffusion models developed by Freed with and without the inclusion of electron spin relaxation effects 54,121).

Cr . Obviously, the incorporation of the hexacyanoferrate ions is preferred. The content of hexacyanochromate in the precipitated solid compound is less than in the solution used for precipitation [35]. 

Potassium hexacyanochromate(III) is available by a literature method.A solution of [Cu(tren)(0H2)][C104]2 is prepared by mixing aqueous solutions of Cu(C104)2 6H20 (2.60 g, 7.00 mmol) in 20 mL of water and tren (1.02g, 6.98 mmol) in 10 mL of water. The dropwise addition of a hexacyanochromate(III) solution, prepared by dissolving 0.38 g of K3[Cr(CN)6] (1.16 mmol) in 15 mL of water, to the copper solution results in the immediate formation of a turquoise precipitate. Once the addition is complete, the precipitate is collected by filtration washed successively with cold water, ethanol, and ether and then air-dried to afford a blue powder of [ Cu(tren)(CN) 6Cr][C104]9 H2O Yield 1.50 g, 55%. 

Potassium hexacyanochromate(III) is a yellow solid, highly soluble in water, that crystallizes as large square platelets. It crystallizes in the orthorhombic system, with the space group Pcan. The unit parameters are a = 8.53, b = 10.60, c = 13.68 A. Because of its disorder behavior, it presents a complex crystallographic problem. The compound shows a j/cn band at 2131 cm. The molar extinction coefficients in aqueous solution of the two observable d d bands at 376 nm ( A2g —> 72) and 309 nm (4 2 T l ) are 93 and 62 L mol ... 

The C-enriched hexacyanochromate(III), K3[Cr( CN)g], is obtained by following a similar synthetic route. When 0.230 g of chromous(II) acetate complex is used in the reaction with 1 g of C-enriched potassium cyanide, then 0.198 g... 

In hexacyanochromate (III) ion, the lowest doublet and quartet ex- ited states are well separated (Section 8.6). By the use of suitable sensitizers, it is possible to excite the two states separately. By such techniques, it has been established that photoaquation of cyanide ion occurs from the excited quartet state 4T , whereas E state is photochemically inactive and the seat of phosphorescence emission. The intersystem quartet to doublet crossing is not always fast. 

Attempts to isolate pure cyanochromium(II) complexes from the deep red solutions containing [Cr(CN)6]4 ions formed when chromium(II) acetate is added to aqueous potassium cyanide in excess, and in other ways, have not been very successful. Now, through careful control of concentration and of pH, the known but poorly characterized green crystalline hexacyanochromates(II) M4[Cr(CN)6]-2H20 (where M = Na or K), the new dark green simple cyanide Cr(CN)2-2H20, and their anhydrous forms have been prepared pure (Scheme 1 and Table 2).10... 

In liquid ammonia, hexacyanochromates(II) can be reduced to the diamagnetic chromium(O) complexes M6[Cr(CN)6] by the appropriate alkali metal. The K salt was earlier obtained by reduction of K3[Cr(CN)6], Greater metal-ligand jt bonding is presumably responsible for the lower CN stretching frequencies of M6[Cr(CN)6]. The potassium salt is oxidized to K3[Cr(CN)6] by ammonium cyanide in liquid ammonia (equation l).12... 

Use the information in Table 16.4 to write the formula for each of the following coordination compounds (a) potassium hexacyanochromate(III) ... 

The preferred methods of preparation of catalysts based on the hexacyanocobaltate and hexacyanochromate ions were with the respective acids. However, because of the instability of the acid of the latter ion, successful use depended upon using it immediately after preparation. No satisfactory preparation of a catalyst using the hexacyanoferric acid was developed. 

Cr CN)s] 6(CI04)3 showing the intermolecular interactions between six dinuclear Cu —Cr units (a), which lead to the formation of a cyclic dodecanuclear supramolecular complex (b), which is cocrystallized with a heptanuclear supramolecular cation that consists of a central hexacyanochromate fragment surrounded by six weakly interacting Cu(II) units (c). 

Lazarides, T., Davies, G.M., Adams, H., et al. (2007) Ligand-field excited states of hexacyanochromate and hexacyanocobaltate as sensitisers for near-infrared luminescence from Nd(III) and Yb(III) in cyanide-bridged d-f assemblies. Photochemistry and Photobiological Sciences, 6, 1152. 

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