In solvent⁃free condition, a new 1D chain holmium phosphite Ho(H2PO3)4(C6N2H16)0.5 (compound 1) decorated by phosphite groups has been synthesized using N,N'⁃Dimethylpiperazine (Me2ppz) as structure directing agent, and further been characterized by powder XRD, infrared spectroscopy, thermogravimetric, inductively coupled plasma and CHN elemental analyses. Single crystal X⁃ray diffraction analysis reveals that compound 1 crystallizes in the monoclinic crystal system with the P21/c space group. The structure of compound 1 is constructed by HoO6 octahedra and [H2PO3]- pseudo⁃pyramids units via vertex oxygen atoms. It is worth noting that compound 1 is the first rare earth phosphite compound which is synthesized in solvent⁃free condition. Moreover, a pair of left⁃ and righ⁃handed helical chains are present in the structure. In addition, coordination mode and geometry of lanthanide phosphonate, phosphate and phosphite are listed in this paper.

Phosphate is an important multifunctional crystal material with broad application prospects in catalysis, photoluminescence, gas storage and separation. In recent years, many phosphate compounds and their derivatives have been used in the study of proton conducting materials. In this paper, the mechanism of proton conduction is briefly introduced. From the operating temperature, the phosphate is divided into two categories with 100 ℃ as the demarcation point. The research progress of phosphate as proton conducting material is introduced, and the challenges faced by phosphate as proton conduction material are prospected.