3D coordination polymer of [HW₇O₂₄]^5- stabilized by a copper(II) complex and sodium cations: Structure, solid-state stability, and aqueous solution behavior

Compound Na[Cu(en)₂]₂[HW₇O ₂₄]·5H₂O (1, en = ethanediamine), as the first example of a heptatungstate polymer, has been synthesized in H₂O/dmso and characterized by single-crystal X-ray diffraction, IR, UV/Vis, and ESI-MS. The [HW₇O₂₄]^5- cluster in 1, as an inorganic hexadentate ligand, coordinates to two Na⁺ and four [Cu(en) ₂]²⁺ cations to construct a 3D extended structure. The solid-state stability of 1 at room temperature was proven by X-ray powder diffraction and digital camera techniques. The electrospray mass spectra suggest that most of the [HW₇O₂₄]^5- dissociates into relatively more stable [W₆O₁₉]^2- species in aqueous solution because the coordination bonds around the [HW₇O ₂₄]^5- anions are broken by the solvation effect of water on the the copper cation. These results demonstrate that a transition-metal- complex cation plays an important role in the isolation and stabilization of a highly charged polyoxometalate anion.