The effects of pH values on the formations of water soluble calcium 1,3-propylenediaminetetraacetates

摘要

A series of pH dependent water soluble calcium 1,3-propylenediaminetetraacetates [Ca(1,3-H(4)pdta) (NO3)(2)(H2O)(2)](n) (1), [Ca(1,3-H(2)pdta)](n)center dot nH(2)O (2), K-4[Ca-2(1,3-pdta)(2)]center dot 2H(2)O center dot 2CH(3)OH (3) and Ca-2(H2O)(6)[(Ca-2(1,3-pdta)(2)(H2O)(2)center dot 4H(2)O (4) have been obtained from the direct reactions of calcium salts with 1,3-propylenediaminetetraacetic acid in different pH values and solvents respectively (1,3H(4)pdta = 1,3-propylenediaminetetraacetic acid). 1 is composed of one-dimensional chains bridged by 1,3-H(4)pdta, where only two strong coordination sites are offered by 1,3-H-4 pdta ligands. While complex 2 features a three-dimensional (3D) structural motif and 3 forms a 2D structure. 4 also contains one-dimensional chain constructed by dimeric calcium 1,3-propylenediaminetetraacetates. Solution C-13 NMR spectra show that dimeric units in 3 dissociate into monomeric species in solution, which indicates that monomeric chelate is a dominant species in neutral and weak basic solution. It is notable that an obvious downfield shift (Delta delta = 2.09 ppm) is observed for methanol in 3 that differs from methanol in D2O solvent. (C) 2016 Elsevier B.V. All rights reserved.