The crystal structure of the layered acid phosphate, AlH2P3O10.2H2O, has been determined and provides a new structure-type for a series of metal phosphates with interlamellar regions likely to be highly suited to intercalation behaviour.

Two previously uncharacterized members of the Rb-Mn-P-O system, RbMnP(2)O(7) and beta-RbMnHP(3)O(10), have been synthesized using a phosphoric acid flux synthetic route and their crystal and magnetic structures determined using neutron powder diffraction. The crystal structure of RbMnP(2)O(7) (space group P2(1)/c, a = 7.3673(2) A, b = 9.6783(2) A, c = 8.6467(2) A, and beta = 105.487(1) degrees) was found to be isostructural with RbFeP(2)O(7). The polymorph beta-RbMnHP(3)O(10) was also isolated as a single phase and found to crystallize in the space group C2 (a = 12.2066(5) A, b = 8.5243(3) A, c = 8.8530(4) A, beta = 107.233(2) degrees). Both structures consist of frameworks of corner-sharing MnO(6) octahedra linked together by condensed phosphate anions, with Rb(+) cations located in the intersecting channels. In both cases the Mn(3+) octahedra exhibit unusual Jahn-Teller distortions indicative of a plasticity effect driven by the steric requirements of the condensed phosphate anions, and this causes a strong violet coloration similar to that observed in the manganese violet pigment; the structure of this has yet to be determined. Magnetic susceptibility measurements show that both RbMnP(2)O(7) (T(N) = 20 K) and beta-RbMnHP(3)O(10) (T(N) = 10 K) undergo a phase transition at low temperatures to an antiferromagnetically ordered state. Low-temperature neutron powder diffraction studies show that the magnetic ground states of each of these materials involve both ferromagnetic and antiferromagnetic super-superexchange interactions between orbitally ordered Mn(3+), which are mediated by PO(4) tetrahedra. These interactions are compared and discussed.

Jahn-Teller Distorted Frameworks and Magnetic Order in the Rb-Mn-P-O System. -RbMnP2O7 (I) and β-RbMnHP3O10 (II) are obtained from solutions of Rb2CO3 and Mn2O3 in 85 wt.% aq. H3PO4 using a Rb:Mn:P ratio of 9:1:15 and 7:1:15, resp. (250°C, 48 h). The compounds are characterized by X-ray and neutron powder diffraction. (I) crystallizes in the space group P21/c and (II) in the space group C2. Both structures consist of frameworks of corner sharing MnO 6 octahedra connected by condensed phosphate anions, with Rb + cations located in the intersecting channels. The octahedra exhibit unusual Jahn-Teller distortions in both compounds. Magnetic susceptibility measurements reveal that both compounds undergo a phase transition to an antiferromagnetically ordered state at low temperatures.

Structure D 2000Synthesis and Crystal Structure of AlH 2 P 3 O 10 ·2H 2 O; a New Structure-Type for Layered Acid Phosphates. -The title compound is synthesized from a phosphoric acid flux reaction starting with H3PO4 and Al2O3 in a molar ratio of P:Al = 6:1 (240°C, 24 h). AlH2P3O10·2H2O crystallizes in the monoclinic space group P2/c with Z = 2 (single crystal XRD) and represents a new structure-type for the layered compounds MH 2 P 3 O 10 ·nH 2 O (M: Ga, Fe, Mn, V, Cr). The structure contains two-dimensional layers of H2P3 units, providing octahedral coordination to the Al 3+ ions. AlH2P3O10 has already commercial applications as an environmentally-friendly anticorrosion pigment in paints and coatings for metal surfaces and as an adsorbent. -(RISHI, S. K.; KARIUKI, B. M.; CHECKER, N. J.; GODBER, J.; WRIGHT*, A. J.; Chem.