Weakly Coordinating Borophosphates – Ca0.5M(H2O)2[B(PO4)2]•H2O (M = Mg, Mn, Co, Zn, Cd)

Abstract

Up to now, a considerable number of borophosphates have been reported, despite the young history of this material class.However, detailed Tanabe-Sugano analyses to investigate the coordination strength of the host structures have barely been reported yet. Herein, the series Ca0.5M(H2O)2[B(PO4)2]•H2O with M = Ni, Fe was extended by introducing further metal cations with M = Mg, Mn, Co, Zn, Cd; the M atoms are coordinated octahedrally by oxygen and water. Thus, the reflection spectra for M = Mn, Co were elucidated by determining the Racah parameter and the ligand field splitting of the d-orbtials which revealed that borophosphates can be classified as weakly coordinating host materials. The crystal structure contains corner sharing borate and phosphate terahedra forming one-dimensional helical chains with water molecules inside those helices.Single-crystal data revealed the presence of systematically absent reflections in the original space group P6122 which was solved by losing the twofold axis, whereby the structure was refined in the trigonal subgroup P3121. Next to single-crystal XRD and UV-vis spectroscopy, the titled compounds were further characterised by powder XRD, FT-IR spectroscopy and thermal analysis.