New rubidium zinc hydrogen phosphate, Rb2Zn2(HPO4)(3): Synthesis, crystal structure, and P-31 single-crystal NMR

A new rubidium zinc hydrogen phosphate, Rb2Zn2(HPO4)(3), is prepared by an unusual method utilizing long nucleation times. This material is crystalliz ed from a gel with an initial composition of 1.0 ZnO/0.94 P2O5/0.96 Rb2O/0. 04 Li2O/41 H2O, while the phosphate concentration equals 1.6 M and pH = 3.5 . The gel is placed in a sealed Pyrex flask at 52 degrees C, and after 4.5 months crystallization of Rb2Zn2(HPO4)(3) is noticed. This new crystalline compound has a three-dimensional framework structure built from spiral chai ns of alternating PO4 and ZnO4 tetrahedra connected pairwise and assembled by other PO4 tetrahedra, rubidium ions, and hydrogen bonds. The two rubidiu m ions, Rb(1) and Rb(2), have an exceptionally low number of oxygen contact s in the first coordination sphere, five and seven, respectively. Crystal d ata: monoclinic, P2(1)/c (no. 14), a = 12.5880(4), b = 12.7170(8), 7.5827(8 ) Angstrom, beta = 96.100(1)degrees, Z = 4. A single-crystal P-31 NMR inves tigation of Rb2Zn2(HPO4)(3) was performed employing a two-axis goniometer p robe and reveals the presence of three chemically and six magnetically none quivalent phosphorus sites, in accordance with the crystal structure. P-31 chemical shielding anisotropies and isotropic chemical shifts (-3.3(3), -2. 6(3), and 2.0(3) ppm) have been determined for the three phosphorus sites.