Chromium complexes nitrito

Gnmwald-Winstein analysis, 505 Chromium(III) complexes doublet excited states reactions, 400 emission rules, 395 ligand field states reactivity, 397 magnetic behavior, 272 mixed-ligand reactivity, 398 nitrito... 

Aquation of the nitrito-complexes [Cr(ONO)(NH3)5] + (ref. 100) and [Cr(ONO)(OHa)5] + (ref. 101) is unexpectedly fast. In these cases, aquation takes place without chromium-oxygen bond breaking. Moreover, the aquation of [CrX(OH2)5] , X = Cl or Br, is specifically catalysed by nitrous acid. This is explained by ready formation of [CrX(ONO)(OH2)4]+ as an intermediate, by direct attack of nitrous acid on co-ordinated water again without chromium-oxygen bond fission. The suggestion is supported by the observation that aquation of [CrBr(NHa)5] + is not accelerated by nitrous acid. ... 

According to Beck et al [Ra 76], this catalytic effect can be explained in that the carbonato or nitrito complex of chromium is formed without splitting of the inert Cr—O bond in the hexaquo complex (in effect, in an oxygen-exchange reaction). 

Oxoanions. Aquation of the four nitrito-chromium(m) complexes listed in Table 9, in acid solution (pH< 1), follows the rate law... 

Table 9 Kinetic parameters for aquation of nitrito-chromium m) complexes kx and k% are defined by the rate law cited in the text, MI and AS are derived from the respective kx and kz values. Rate constants are quoted at 25 °C ...

Earlier kinetic results for aquation of a variety of nitrito-chromium(in) complexes are tabulated in ref. 159. 

A third recent example of such cis labilization is provided by the (formation) reactions of edta with [Cr(OH ) ] and with carboxylato-complexes [Cr(0Hj)6(02CR)] +. In the latter cases, the observed faster rates of replacement of water have been ascribed to an analogous cis anchimeric effect to that operating in the ammine aquations mentioned (M. V. Olson, Inorg. Chem., 1973, 12, 1416). This type of anchimeric effect has been observed previously, as for example in the rapid aquation of 0-nitrito-chromium(m) complexes [T. C. Matts and P. Moore, J. Chem. Soc. (A), 1971, 1632]. 

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