Heterocyclic Carboxylates of Nb(V) and Ta(V)

The reactions of niobium and tantalum pentaethoxides and pentachlorides with 2-thiophenecarboxylic acid (HTCA) and 2-thiopheneacetic acid (HTAA) were carried out in different stoichiometric ratios. Complexes of the type M (OEt)5-n (L)n (n = 1–3 and M = Nb or Ta) and MC15-n Ln (n = 1 or 2 and M = Nb or Ta) were obtained and characterised on the basis of elemental analyses and spectral (i.r. and 1H n.m.r.) data.