Synthesis and structures of three 1-aminoethylidenediphosphonate compounds with transition-metal ions

Three new aminodiphosphonates, namely M(phen)(AEDPH3)2·4H2O (M = Zn, (1); Ni, (2)) and Cu(phen)(AEDPH3)2·H2O (4), in addition to the previously reported Co(phen)(AEDPH3)2·4H2O (3), Cu(2,2′-bipy)(H2O)(HEDPH2)·2H2O (5), and Cu(phen)(H2O)(HEDPH2)·2H2O (6) (AEDPH4 = 1-aminoethylidenediphosphonic acid, HEDPH4 = 1-hydroxyethylidenediphosphonic acid, phen = 1,10-phenanthroline and 2,2′-bipy = 2,2′-bipyridyl), have been synthesized and characterized. These compounds are all synthesized at the similar condition (80 °C), whereas they illustrate different frameworks. Compounds 1, 2 and 3 are isomorphous, which contain two same chelate AEDPH 3 - and one six-coordinated metal ion, and display a three-dimensional (3D) supramolecular structure through hydrogen bonds and π–π stacking interactions. Compound 4 contains a chelate and a monodentate AEDPH 3 - , while the Cu ion is five-coordinated. The coordination model of Cu2+ in 4 is similar to that of 5 and 6. Comparing with four aminoethylidenediphosphonates, the difference of their structures is directed to the coordination model of the metal ions, while the three copper(II) diphosphonates illustrate different structures based on the deprotonized degree of the corresponding diphosphonic acids.