Organotemplate-free synthesis of two open-framework metal borophosphates

Abstract

Two new isostructural metal borophosphates, |K₂(H₂O)|[CoB₂P₃O₁₂(OH)] [M = Co (1), Ni (2)], have been hydrothermally synthesized with non-polluting K⁺ ions instead of organic template-ethylenediamine. The two metal borophosphates are isostructural and constructed by the connection of tetrahedral layers and MO₆ octahedra, giving rise to the 3-D intersecting 8-ring channels along the [010] direction. The negative charge of the framework is compensated by the K⁺ ions located in the 8-ring channels. Like ethylenediamine, the K⁺ ions also play an important structural directing role in the formation of the open framework. The framework shows a high thermal stability and is stable upon calcination at ca. 400 and 500 °C for 1 and 2, respectively. Considering the motion of K⁺ ions, ionic conductivities of the two compounds were performed. The results indicated that they have similar activation energies of 0.94–1.09 eV and conductivities of 6.76 × 10⁻⁸–9.88 × 10⁻⁸ S cm⁻¹ at 320 °C.