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Crystals of synthetic Mg-whitlockite, Ca,8Mg2H2(P04)14, have been grown by hydrothermal techniques and their structure refined by full-matrix least-squares methods, using 1626 unique reflections measured with a Syntex PT automatic diffractometer, to a final R value of 0.046. The crystals have space group R3c with Z, = 1, a = 13.765(8) A and a = 44.25(5)" with the equivalent hexagonal parameters a = 10.350(5), c = 37.085(12) A and ZFl = 3. The structure, although similar to that of (3Ca3(P04),, differs significantly. The structure contains interconnected infinite chains of polyhedra paralleling the hexagonal c axis with links in the chains consisting of three CaO, polyhedra separated by two PO, tetrahedra. Six of these chains surround a chain of M g 0 6 octahedra and P 0 4 H groups which lie on the three-fold axes. These chains however contain only half the formula unit density of the calcium containing ones and a proton, presumably disordered, is attached to the oxygen atom on the triad axes.Des cristaux de Mg-whitlockite synthetique Ca18MgZH2(P04)14 ont it6 developpes par des techniques calorimetriques et leur structure raffinee par une matrice complete des methodes de moindres carris, utilisant la reflection unique 1626 mesurke par un diffractornetre automatique

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STRUCTURE CRISTALLINE DE L'HYPOVANADATE CaV409pliquant bien pour celui-ci non pas un environnement octa6drique mais un environnement pyramidal b. base carr6e.(~ 2')~ 3, 06 CusV2Ol0 is monoclinic with a=8"393 (2), b=6-0652 (8), c= 16.156 (3)~, fl= 108"09 (2) °, Z=4, and space group P2~/c. The crystal structure was refined by full-matrix least-squares analysis to a wR = 0.032 using 1629 reflexions measured on a Syntex automatic diffractometer. The structure consists of a network made up of double chains of Cu-O6 octahedra running parallel to b and chains forrned from Cu-O6 octahedra and Cu-O5 trigonal bipyramids running parallel to c. These chains are linked to each other by edge sharing of the octahedra and trigonal bipyramids and corner sharing of the V(2)Oa tetrahedra. Two such networks at x= ¼ and k are linked by the V(1)O4 tetrahedra. Cu(1) and Cu(2) are octahedrally coordinated by oxygen atoms and show typical Jahn-Teller distortion. Cu(4) is also octahedrally coordinated but has an unusual distortion in which one equatorial and one apical, rather than 2 apical Cu-O bonds, are elongated. The mean Cu-O distances differ significantly for the three octahedra. These differences and those in other Cu-containing oxides are related to the degree of distortion of the octahedra. Cu(3) and Cu(5) are each surrounded by five oxygen atoms in the form of distorted trigonal bipyramids. The apical bonds are shorter than the equatorial bonds as in Cu2OSO4, CHaAszOs and Cu3WO 6. The differences in individual V-O distances are related to the bond-strength sums around the oxygen atoms.

a-VPO, crystallizes in the tetragonal space group P4/n with a = 6.014(7) and c = 4.434(2) A. The structure, isotypic with that of a-VS05, was refined by full-matrix least-squares method to an R value of 0.089 using 239 independent reflections. The vanadium ion lies on a crystallographic four-fold axis, as does one of the oxygen atoms, and the P on a site of 4 symmetry. A second oxygen atom, as a result of disorder, occurs in two positions which are mirror reflected with respect to the ac plane. The structure consists of highly distorted V 0 6 groups with bond lengths along the c axis of 1.580(11) and 2.853(11) A while the remaining four V-0 bond lengths are all 1.858(8) A. The P-0 bond lengths in the PO4 tetrahedron are 1.541(8) A with the PO4 groups bridging across four chains of V 0 6 groups.L'aVPOs cristallise dans le groupe d'espace tetragonal P4/n avec n = 6.014 (7) [Traduit par le journal]Can.

Magnesium orthovanadate crystallizes in the orthorhombic space group Cmca with a = 6.053(3), b = 11.442(6), c = 8.330(3) Å, and Z = 4. The structure was refined by full matrix least square methods to a final R value of 0.047 using 1697 reflections measured by a quarter circle General Electric automatic diffractometer. The structure was assumed to be isomorphous with that of Ni3(VO4)2, reported by Durif and Bertaut (2), and the refinement started using the same fractional atomic coordinates. The structure consists of nearly cubic closest packing of oxygen atom layers roughly normal to the [Formula: see text] direction with the Mg ions in two types of octahedral sites and the V ion in a tetrahedral site. The VO4 group has a crystallographic mirror plane. The cations lying on sites of Cm symmetry show an average Mg—O bond length of 2.092 Å, compared to 2.098 Å for cations lying at sites of C2h symmetry. The anion deviates significantly and substantially from regularity with the three oxygen atoms shared with only two cations showing V—O bond lengths within 0.015 Å of their mean, 1.70 Å, whereas the remaining oxygen atom, which is shared with three Mg ions, lies 1.809 Å from the V ion. The structure has characteristics similar to those of spinel.

KAIP207 crystallizes as monoclinic crystals with a = 7. 308(8), b = 9.662(6), c = 8.025(4) A, = 106.69(7)", z = 4 and space group P2Jc. The structure was refined from 1394 observed reflections by fullmatrix least-squares method to a final R value of 0.032. The P2074-anion consists of a pair of cornersharing PO4 groups in a nearly staggered configuration. The mean bridging and terminal P-0 bond lengths are 1.607 and 1.509 A, respectively, and the P-0-P angle is 123.2". The anions lie in planes parallel to (001). The A1 ions are bonded to six oxygen atoms contributed by anions in three layers of P 2 0 7 groups. The average AI-0 bond length is 1.889 A. The potassium ion is coordinated to ten oxygen atoms lying within a spherical shell with inner and outer radii of 2.739 and 3.185 A. Can.