Niobium complexes fluxionality

A range of other cationic niobium and tantalum tetrakis(dithiocarbamate) complexes, [M(S2CNR R )4]X (M = Nb, Ta R = R = Me, f-Bu R = Me, R = I -Pr, Ph, Cy, Bz), have been prepared from the metal pentachlorides and anhydrous dithiocarbamate salts (719). They are fluxional on the NMR time scale, a polytopal mechanism being proposed via a cubic or square antiprismatic transition state. The kinetics of this process has been studied by total line shape analysis, giving AG values of 42-50 kJ moP. ... 

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