~9Be and ~(31)P NMR analyses on Be~(2+) complexation with cyclo-tri-μ-imidotriphosphate anions in aqueous solution

摘要

Microscopic information on the complexation of Be~(2+) with cyclo-tri-μ-imidotriphosphate anions in aqueous solution has been gained by both 9Be and 31P NMR techniques at -2.3 °C. Separate NMR signals corresponding to free and complexed species have been observed in both spectra. Based on an empirical additivity rule, i.e., proportionality observed between the 9Be NMR chemical shift values and the number of coordinating atoms of ligand molecules, the 9Be NMR spectra have been deconvoluted. By precise equilibrium analyses, the formation of [BeX(H _2O)_3]~+ and [BeX_2(H _2O)_2]~0 (X = non-bridging oxygen donor as a coordination atom in the phosphate groups) has been verified, and the formation of complexes coordinating with the nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. Instead, the formation of one-to-one (ML) complexes, one-to-two (ML2), together with two-to-one (M 2L) complexes (L = cP_3O_6(NH)_3) has been disclosed, the stability constants of which have been evaluated as log KML = 3.87 ± 0.03 (mol dm-3)-1, log KML2 = 2.43 ± 0.03 (mol dm~(-3))~(-2) and log KM2L = 1.30 ± 0.02 (mol dm~(-3))~(-2), respectively. ~(31)P NMR spectra measured concurrently have verified the formation of the complexes estimated by the 9Be NMR measurement. Intrinsic ~(31)P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be2+, together with the ~(31)P-~(31(P spin-spin coupling constants have been determined.