Uranyl compounds bond lengths

Rare organoimides U(MeCp)3(=NR) have been made by oxidation of U(MeCp)3(thf) with RN3 (R = MesSi and Ph). The U-N bond length of 2.109 A is regarded as having multiple-bond character (cf. the U=0 bond in uranyl compounds). 

Bond length correlations with either force constants or with the symmetric or antisymmetric stretching frequency have recently been reviewed [91]. A survey of 27 uranyl compounds gives a satisfactory correlation between the symmetric stretching frequency and the bond lengths determined by diffraction methods with the form ... 

The Fourier transform moduli of EXAFS data of three silica samples that sorbed U(VI) appeared to be very similar (Fig. 3-5). The uranyl U=0 distance of 1.78 0.01 A is typical of U(VI) compounds. Shells for hydroxide coordinated in the equatorial plane appeared in the range 2.22 to 2.31 A, while bond distances for coordinated water molecules were observed from 2.43 to 2.51 A. The presence of a U-Si shell (between 3.1 and 3.3 A) in all samples investigated suggests the formation of inner-sphere uranyl surface complexes, and there was no evidence for a U-U shell, which would indicate surface precipitation or polynuclear uranyl species. The short U-Si bond length of about 3.2 A and coordination number of 1 at pH around 3 suggests bidentate complexation to a single silica atom. At pH 5, the coordination number of 2 for the Si shell suggests the coordination of the uranyl complex to two Si atoms (Sylwester et al., 2000). 

---