Bastian Ewald

Characterization of local environments in crystalline borophosphates using single and double resonance NMR

(11)B and (31)P magic-angle spinning as well as (11)B{(31)P} and (31)P{(11)B} rotational echo double resonance (REDOR) NMR have been applied to characterize the local environments in the crystalline borophosphates K(3)[BP(3)O(9)(OH)(3)], NH(4)[ZnBP(2)O(8)] and Rb(3)[B(2)P(3)O(11)(OH)(2)]. Dipolar second moment values extracted from the REDOR curves at short evolution times (DeltaS/S(0) < or = 0.2) are in reasonable agreement with those calculated from the internuclear distances in the corresponding crystal structures. In particular, the method is found to be useful for distinguishing between boron and phosphorus local environments with different numbers of B-O-P connectivities, making REDOR a well-suited tool for medium-range order investigations in glasses.

Refinement of the crystal structures of praseodymium- and samarium-oxoborate-bis(oxophosphate)-oxide, Ln7O6[BO3][PO4]2, (Ln = Pr, Sm)

BO 17 P 2 Pr 7 , monoclinic, P12 1 /n1 (no. 14), a = 6.8939(4) A, b = 17.662(1) A, c = 12.442(1) A, β=97.24(1)°, V= 1502.9 A 3 , Z=4, R gt (F) = 0.029, WR ref (F 2 ) = 0.052, T = 293 K. BO 17 P 2 Sm 7 , monoclinic, P12 1 /n1 (no. 14), a = 6.7781(7) A, b = 17.396(1) A, c = 12.218(1) A, β=96.96(1)°, V= 1430.0 A 3 , Z=4, R gt (F) = 0.022, WR ref (F 2 ) = 0.044, T = 293 K.

Crystal structure of sodium scandium bis(monohydrogenphosphate), NaSc(HPO4)2

H2NaOgP2Sc, monoclinic, Clc l (no. 9), a = 10.4446(9) A, b = 16.371(2) A, c = 9.0553(7) A, ß = 122.420(3)°, V= 1307.1 Ä 3 ,Z= 8, Rgl(F) = 0.023, wRrerfF) = 0.054, T= 293 K. Source of material Single crystals of NaSc(HPC>4)2 were obtained as minority phase during hydrothermal investigations in the system Na20-Sc2Qj-B20jDiscussion The number of scandium phosphates is comparatively small, although they attracted attention as ionic conductors [1-4]. Also complex scandium phosphate frameworks have been reported recently [5,6]. Acid quasi-ternary scandium phosphates have never been investigated systematically and NaSc(HP04)2 represents the first acid alkali metal scandium phosphate. Monohydrogenphosphates with the general composition AiAi(HP04)2 known up to date are: (NH4)Fe(HP04)2 [7], RbFe(HP04)2 [8], (NH4)In(HP04)2 [9], LiIn(HP04)2 [10] and MV(HP04)2 (M = NH4, Rb [ 11 ], Af=NH4 [ 12]). All these structures comprise complex partial structures of alternating A ^ O i octahedra and HPO4 tetrahedra that, connected via common comers, build fourmembered rings of polyhedra. Only the crystal structure of LiIn(HP04)2 [10] contains an anionic arrangement which is identical to that of the title compound (in terms of topology), but not isotypic. The crystal structure of NaSc(HP04)2 was solved in the acentric space group Clcl [Flack parameter x = 0.02(2)]. It comprises scandium in sixfold coordination by oxygen with Sc—O distances ranging from 1.996(2) A to 2.146(2) A. Each corner of these distorted octahedra (¿O-Sc-O = 82.80(6)° 96.30(6)° for adjacent oxygen atoms) is shared by a HP04 group. The hydrogenphosphate tetrahedra (d(P—O = 1.506(2) A 1.594(2) A, ¿ O P O = 103.15(9)° -113.49(9)°) themselves share the three unprotonated oxygen atoms with adjacent Sc06 polyhedra. In this manner sixand four-membered rings of alternating octahedra and tetrahedra are formed. As a linear arrangement of the fourmembered rings is found (equatorial positions of the Sc06 octahedra), it is possible to describe the structure by a ladder motif (figure, top) which is a common structural feature in many phosphates. These polyhedral ladders can either be isolated or connected to sheets or 3D networks [13,14]. The title compound comprises waved ladders running along [100] that are connected to adjacent ladders (perpendicular in latitudinal direction) via the apical oxygen atoms of the ScC>6 octahedra forming a 3D network. Sodium is located in the cavities of the network (figure, bottom) and is sixto sevenfold coordinated by oxygen in the Na—O distance range between 2.3 A and 3.0 A. * Correspondence author (e-mail: kniep@cpfs.mpg.de)

Refinement of the crystal structure of diniobium trisoxydisulfate hydrate, Nb2O3(SO4)2 . 0.25H2O

H0.5Nb2O11.25S2, trigonal, R3 (no. 148), a = 10.378(2) A, c = 26.540(5) A, V = 2475.7 A 3 , Z = 24, Rgt(F) = 0.031, wRref(F 2 ) = 0.072, T = 295 K. Source of material Single crystals of the title compound were obtained by evaporation of a solution of niobium oxide in sulfuric acid. Typically, 1.000 g (3.762 mmol) Nb2O5 (Chempur, 99.9 %) and 100 ml H2SO4 (95 % – 97 %, Merck, p.a.) were mixed and heated at 523 K while stirring. When the niobium oxide was completely dissolved, the colourless solution was kept at 523 K to allow the acid to evaporate until it turned slightly yellowish and first signs ofprecipitationweregivenbyturbidity.Thishighlyconcentrated