Synthesis and Structure Determination of Rb2(HSO4)(H2PO4) and Rb4(HSO4)3(H2PO4) by X-Ray Single Crystal and Neutron Powder Diffraction

Two new compounds, Rb2(HSO4)(H2PO4) and Rb4(HSO4)3 (H2PO4), were synthesized from aqueous solutions of RbHSO4/RbH2PO4. The compounds were characterized by X-ray single crystal analysis and neutron powder diffraction. For Rb2(HSO4)(H2PO4), room temperature and a low temperature modification were found. According to X-ray crystal structure analysis, the compounds have the following crystal data: Rb2(HSO4)(H2PO4) (T=298 K), monoclinic, space group P21/n, a=7.448(3) Å, b=7.552(2) Å, c=7.632(3) Å, β=100.47(3)°, V=422.1(3) Å3, Z=2, R1=0.033; Rb2(HSO4)(H2PO4) (T=160 K), monoclinic, space group P21/c, a=11.555(3) Å, b=7.536(2) Å, c=9.593(2) Å, β=91.56(2)°, V=853.0(4) Å3, Z=4, R1=0.041; Rb4(HSO4)3(H2PO4), orthorhombic, space group P21212, a=7.612(6) Å, b=14.795(9) Å, c=7.446(4) Å, V=838.6(9) Å3, Z=2, R1=0.045. The compounds have different coordination numbers of rubidium, being 7, 8, 9, or 10 with Rb–O distances from 2.9 to 3.3 Å. In all cases there were difficulties in the allocation of sulfur and phosphorus due to the small differences in their radii and scattering factors. All structures are characterized by HSO4− and H2PO4−, or disordered HxS/PO4− tetrahedra connected to zigzag chains via hydrogen bridges. These chains are linked by additional hydrogen bonds to a layer-like hydrogen bonding system.