The molten hydrated flux synthesis of a novel open-framework copper borophosphate and its structural relation with the precursors

A novel copper borophosphate, Cu2(H2O)[BP2O7(OH)], has been synthesized by the molten hydrated flux method. Its crystal structure (Orthorhombic, Pbca, a=8.234Å, b=9.655Å, c=17.805Å, V=1415.485Å3, Z=8) can be regarded as the condensation of alternately edge- and corner-shared copper pyramidal chains and borophosphate chains formed via vertex-sharing PO4 and BO3(OH) tetrahedra. Magnetic measurements indicate that antiferromagnetic interactions exist in the title compound. Due to the special reaction medium created by the molten hydrated flux method, a possible structural correlation between final solids and raw materials has been discovered even though no ordered structural fragments exist in the latter. Structure comparison of Cu(NO3)2·3H2O, Cu(NO3)2·H2O and Cu2(H2O)[BP2O7(OH)], showing the structural evolution of CuO5 pyramids in the synthetic process. [Display omitted] •A novel copper borophosphate has been synthesized by the molten hydrated flux method.•Magnetic measurements show its antiferromagnetism at low temperature.•A structural relation between the precursor and the final solid is discovered.