Dinitrogen ligand coordination

A second, independent spectroscopic proof of the identity of 4 as rans-[Mo(N2)2(weso-prP4) was provided by vibrational spectroscopy. The comparison of the infrared and Raman spectrum (Fig. 7) shows the existence of two N-N vibrations, a symmetric combination at 2044 cm-1 and an antisymmetric combination at 1964 cm-1, indicating the coordination of two dinitrogen ligands. In the presence of a center of inversion the symmetric combination is Raman-allowed and the antisymmetric combination IR allowed. The intensities of vs and vaK as shown in Fig. 2 clearly reflect these selection rules. Moreover, these findings fully agree with results obtained in studies of other Mo(0) bis(dinitrogen)... 

The coordination of the dinitrogen ligand is maintained when traTO-[Re(N2)Cl(dppe)2] is exposed to NaX salts (X = NCS, NCO , Ns ) in THF/MeOH solutions. The isothiocyanato and azido complexes of type (276) have been studied by X-ray structural analysis.A Re— N2 bond length of 1.951 A is observed for the NCS compound which is somewhat shorter than that in the starting material and indicates a considerable degree of double bond character. 

Figure 15.1.5(f) shows a planar, side-on bonded N2 ligand between two Zr atoms in the compound [Cp"2Zr]2(N2) [Cp" = l,3-(SiMe2)2C5H3], The N-N bond length is 147 pm. Side-on coordination of the dinitrogen ligand appears to be important for its reduction. 

Other complexes whose crystal structures have been determined include the tetraphosphorus complex (21),191 and the dinitrogen complex (22).182 The latter complex was originally believed to contain a sideways-on dinitrogen ligand 183 however, once corrections were made for disorder and anisotropy of the dinitrogen ligand, the more usual end-on coordination was proposed.182... 

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