Structure and dynamic behaviour of lanthanide nitrate complexes with bis(diphenylphosphorylmethyl)mesitylene in solutions: The nature of unexpected 31P NMR spectra

The solution structures of the lanthanide complexes, [Ln(L)(NO3)3] and [Ln(L)2(NO3)3], where L = bis(diphenylphosphorylmethyl)mesitylene and Ln = La, Ce, Nd, Er, were investigated by 31P NMR and IR spectroscopy, conductivity and sedimentation analysis. Variable-temperature 31P{1H} NMR spectroscopy was used to identify species present in solution and to monitor their interconversions. The results indicate that equilibrium between molecular complexes [Ln(L)n(NO3)3]0 and cationic species (as ion pairs [Ln(L)n(NO3)2]+ · (NO3)− and as free ions [Ln(L)n(NO3)2]+, throughout n = 1, 2) in solutions can be observed by 31P{1H} NMR spectroscopy due to separate detection of the molecular complexes and cationic species. The chelate coordination of the ligand and nitrate ions is retained in all complex species at ambient temperature except for [Er(L)2(NO3)3]. The crystal structure of [Nd(L)(NO3)3(MeCN)]MeCN was determined by X-ray diffraction.