A Robust Framework Based on Polymeric Octamolybdate Anions and Copper(II) Complexes of Tetradentate N-donor Ligands

Abstract

A new organic-inorganic compound based on octamolybdate building blocks and copper(II) complexes of tetradentate N-donor ligands has been hydrothermally synthesized, namely [Cu(cyclam)]2[Mo8O26]·1.5H2O (1), (cyclam: 1,4,8,11–tetraazacyclotetradecane). Compound 1 has been chemically (elemental and thermal analyses), spectroscopically (infrared spectroscopy), and structurally (single crystal and powder X-ray diffraction) characterized. The crystal packing of 1 shows a covalent framework structure formed by [Mo8O26]n4n− chains running along the 100 direction which are linked to each other through the coordination spheres of {Cu(cyclam)}2+ complexes leading to a three-dimensional open network. This structural assembly generates voids that can be described as a succession of cavities communicated through narrow bottlenecks with approximate cross section of 4 × 7 Å2 where the hydration water molecules are hosted. The robust open structure of 1 remains virtually unaltered upon thermal evacuation of guest solvent molecules at 130 °C, resulting in the anhydrous phase [Cu(cyclam)]2[Mo8O26] (1a) with potentially accessible micropores as demonstrated by single-crystal X-ray diffraction measurements. Electron paramagnetic resonance spectroscopy analysis of 1 has also been assessed.

Keywords

• polyoxometalates
• robust hybrid frameworks
• crystal-to-crystal transformations