Two noncentrosymmetric polyphosphates featuring infinite one-dimensional (PO3)∞ chain, LiMP2O6 (M = Rb, Cs): Synthesis, structure and optical properties

LiMP2O6 (M = Rb, Cs) are isostructural, and crystallize in orthorhombic space group Fdd2 (No.43). In the structure, the PO4 polyhedra are connected through corner-sharing to form 1D infinite (PO3) ∞ chains stretching along the c axis, which are further linked by the LiO4 polyhedra to construct a 3D framework with two types of tunnels. And the Rb atoms are filled in or around the periphery of the tunnels to keep the charge equilibrium.235