Structural and spectroscopic properties of MITh2(PO4)3 (M = Cu+, Ag+, Na+, K+)

Phosphates of general formulae MITh2(PO4)3 where M = Cu+ and Ag+ were synthesized using sol-gel type methods and Cu+/Ag+ ion exchange. Their structures were investigated by X-ray diffraction, FTIR, and 31P MAS NMR spectroscopies. AgTh2(PO4)3 and NaTh2(PO4)3 were found to be isostructural. Their 31P NMR spectra exhibit three resonances agreeing with the noncentrosymmetric space group Cc to which they belong. On the other hand, CuTh2(PO4)3 does not show a real crystallographic resemblance with the other MITh2(PO4)3 phosphates of this family. Its 31P NMR spectrum is similar to that of KTh2(PO4)3 and exhibits two sharp resonances in good agreement with the C2/c space group. Nevertheless, the [PO4] groups in this phosphate are highly distorted because of the linear coordination of the Cu+ copper ions.