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

Abstract A series of pH dependent water soluble calcium 1,3-propylenediaminetetraacetates [Ca(1,3-H 4 pdta)(NO 3 ) 2 (H 2 O) 2 ] n ( 1 ), [Ca(1,3-H 2 pdta)] n ·nH 2 O ( 2 ), K 4 [Ca 2 (1,3-pdta) 2 ]·2H 2 O·2CH 3 OH ( 3 ) and Ca 2 (H 2 O) 6 [(Ca 2 (1,3-pdta) 2 (H 2 O) 2 ]·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 (1,3-H 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 13 C 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 (Δδ = 2.09 ppm) is observed for methanol in 3 that differs from methanol in D 2 O solvent.