Cyanide complexes, isomer shift

Table 2 Mossbauer parameters of some six-coordinate low-spin Fe(II) ions. Note that the isomer shift decreases if the Fe-ligand bonds become more covalent in character. Mossbauer parameters for the cyanide complexes, as weU as those for the phenanthroline complex, were taken from Greenwood and Gihh, which the reader may consult for further references...

The complex [Fe(phen)2(CN)2] shows a smaller chemical isomer shift (0-18 mm s at 300 K) than does [Fe(phen)3](C104)2 (0-31 nun s" ) because of the greater 7i-bonding capabilities of the cyanide. The spectrum of so-called /ra 5 -[Fe(phen)2(CN)2] shows Mossbauer parameters identical to those of the cw-complex and from the arguments in Section 7.4 it can be concluded that the difference is not one of m-/ra j-isomerism [47]. 

K2[Ru(CN)5 NO)], the only fully estabhshed nitrosyl cyanide ruthenium complex, is prepared by reaction of K4[Ru(CN)j] with HN03. Its Mossbauer spectrum, which shows a more positive isomer shift than K4[Ru(CN)g], is ascribed to the greater n acceptor ability of NO" compared to CN . For K4[Ru(CN)5(N02)], prepared by reaction of K2[Ru(CN)5NO] with a decrease... 

The computation of rotational constants Be from the inertia moments I corresponding to the interatomic distances in both types of comple.xes illustrates the situation clearly the cyanide and isocyanide isomers have rotational constants separated by about 0.6 GHz, and this shift upwards for the isocyanide species may be useful for their spectroscopic investigation, as already done for the pair of isomers MgNC and MgCN. Corresponding dipole moments are indicated in this connection. It should be added that the present values are consistent with the experimental parameter B = 4.358596 GHz assigned to a related complex FeCO [34]. 

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