Synthesis and crystal structure of new double indium phosphates M3IIn(PO4)2 (MI = K and Rb)

Double potassium indium and rubidium indium phosphates K3In(PO4)2 (I) and Rb3In(PO4)2 (II) are synthesized by solid-phase sintering at T = 900°C. The compounds prepared are characterized by X-ray powder diffraction (I and II), X-ray single-crystal diffraction (II), and laser-radiation second harmonic generation. Structure I is solved using the Patterson function and refined by the Rietveld method. Both compounds crystallize in the monoclinic crystal system. For crystals I, the unit cell parameters are as follows: a = 15.6411(1) Å, b = 11.1909(1) Å, c = 9.6981(1) Å, β = 90.119(1)°, space group C2/c, Rp = 4.02%, and Rwp = 5.25%. For crystals II, the unit cell parameters are as follows: a = 9.965(2) Å, b = 11.612(2) Å, c = 15.902(3) Å, β = 90.30(3)°, space group P21/n, R1 = 4.43%, and wR2 = 10.76%. Structures I and II exhibit a similar topology of the networks which are built up of { In[PO4]2} (I) and { In2[PO4]4} (II) structural units.