Proton-Rich POM-Type K 12 Mo 8 O 20 (HPO 4 ) 8 (PO 4 )Cl with Ion-Exchange Capabilities.

A proton-rich POM-type molybdenum phosphate K 12 Mo 8 O 20 (HPO 4 ) 8 (PO 4 )Cl was successfully obtained. It crystallizes in a noncentrosymmetric tetragonal space group of P -4 (No. 81) with the unit cell parameters of a = 9.6580(4) Å, c = 14.2607(10) Å, and Z = 1. The occurrence and positions of the light element H in the structure are inferred from single-crystal X-ray diffraction and confirmed by DFT calculations. The hydrogen atoms are found to form hydroxyl bonds with O atoms from P(2)O 4 and P(3)O 4 constituting the [Mo 4 P 4 O 26 H 4 ] 4- layers but are only weakly bound to the isolated P(3)O 4 group through hydrogen bonds. The title compound presents a POM-type framework of corrugated [Mo 4 P 4 O 26 H 4 ] 4- layers with four K + ions and mixed ions (K 4 Cl 3+ and isolated PO 4 3- ) orderly imbedding in the interlayer spaces with distances of 5.0396 (1) and 5.5966 (3) Å, respectively. The proton-rich nature and the structure feature were further verified by a series of experiments including 1 H, 7 Li, and 31 P MAS NMR spectra, IR spectroscopy, and thermal analysis. Moreover, the weak bonding and large interlayer spaces make K + and H + ions susceptible to exchange with ions of Cs + , Ba 2+ , Zn 2+ , Pb 2+ , Cu 2+ , and Ni 2+ commonly presented in chemical pollutants or nuclear wastes. In addition, the title compound shows a small second-harmonic generation signal, consistent with its noncentrosymmetric structure.