Transition-metal derivatives of arenediazonium ions. Part VII. Fluorine-19 nuclear magnetic resonance and nitrogen-l5 infrared labelling studies on some benzene-, meta-fluorobenzene-, and para-fiuorobenzene-diazo-complexes of iron, molybdenum, platinum, and tungsten
19 F N.m.r. spectra of fifteen different classes of m- and p-fluorobenzenediazo-complexes containing iron, molybdenum, platinum, or tungsten have been measured. The 19F n.m.r. technique is shown to be a sensitive tool for determination of the degree of M–N2Ar π-bonding provided all complexes studied are of the same structural type. Direct evidence has been obtained for the view that the cation ArN2+ is a poorer π-acceptor than NO+. The ν(NN) stretching frequencies of the ArN2 complexes (Ar = Ph, m-FC6H4, or p-FC6H4) have been identified by 15N14N labelling. Many of these complexes show an unexpected multiplicity of bands associated with the N2chromophore.