The pH-Controlled Hydrothermal Synthesis and Crystal Structure of Two Novel Phosphomolybdate Derivatives

Two novel phosphomolybdate derivatives, (H2en)(Hen)2(H2P2Mo5O23)·5H2O (1) and [Cu(phen)(en)][Cu(phen)(en)(H2O)]2[PMo 8 VI Mo 4 V O40{Cu(phen)}2]2·6H2O (2) (en = ethylenediamine, phen = 1,10′-phenanthroline), were synthesized under hydrothermal technique and characterized by crystal X-ray diffraction analysis, elemental analysis, IR and TGA. Compound 1 is constructed from a [H2P2Mo5O23]4− polyoxoanion and one (H2en)2+ cation and two (Hen)+ cations and is a typical Strandberg-type hepteropoly compound. The interaction force between the components are electrostatic force and hydrogen bonds which involve polyoxoanions, water molecules and ethylenediammonium cations. Compound 2 consists of one [Cu(phen)(en)]2+ and two [Cu(phen)(en)(H2O)]2+ cations and two [PMo 8 VI Mo 4 V O40{Cu(phen)}2]3− polyoxoanions. The reduced Keggin polyoxoanion [PMo 8 VI Mo 4 V O40]7− of 2 is capped by two divalent Cu atoms through four bridging oxo groups on two opposite {Mo4O4} faces. The results reveal that the pH plays a significant role in promoting the diversity of structural motifs. The effect of en is not only to ensure the required amounts of ligands for the reaction process, but also to control the pH. In the synthetic process, the control of the reaction conditions plays a crucial role in constructing different structures.