ALUMINUM PHOSPHATES WITH NONCENTROSYMMETR IC LAYER-STRUCTURE AND FRAMEWORK-STRUCTURE OF TOPOLOGICALLY RELATED MOTIFS - 1 - KAL2(PO4)(2)(OH)CENTER-DOT-4H(2)O

KAl2(PO4)(2)(OH). 4H(2)O could be obtained by the reaction of gibbsite with a potassium-phosphate solution of pH = 5.5 at 333 K. A single cr ystal X-ray structure analysis showed that KAl2(PO4)(2)(OH). 4H(2)O is isotypic with the mineral minyulite. Crystal data: orthorhombic space group Pba2, a = 934.7(1), b = 982, 1(1), c = 551,0(1) pm, Z = 2. It p ossesses dimeric units of Al-octahedra which are bridged by an OH-and two bidentate phosphate groups. The dimers are linked by phosphate to plane polar layers. Cavities in the layers are occupied by K ions. One corner of each phosphate tetrahedron is not connected to Al but accep ts four hydrogen bonds from water molecules bound to Al of the adjacen t layer. A powder neutron scattering experiment with KAl2(PO4)(2)(OD). 4D(2)O showed that four D atoms and P coordinate the hydrogen bond ac cepting O in KAl2(PO4)(2)(OD). 4D(2)O like a square pyramid. Analogous dimeric building units are found in the Al phosphate minerals minyuli te and morinite; similar dimers of Fe octahedra occur in the mineral c opiapite, a number of Fe containing enzymes and numerous synthetic iro n complexes. High-resolution P-31 solid-state NMR spectra show only on e isotropic Line at delta(iso) = -9.6 ppm and confirm the presence of one symmetry independent phosphorus site in the unit cell. In the H-1- MAS-NMR spectra the water molecules and the bridging OH groups show si gnals at 5.4 and 1.4 ppm, respectively.