Zoya A. Solodovnikova

Rubidium dimolybdate, Rb2Mo2O7, and caesium dimolybdate, Cs2Mo2O7

The crystal structures of dirubidium heptaoxodimolybdate, Rb(2)Mo(2)O(7), and dicaesium heptaoxodimolybdate, Cs(2)Mo(2)O(7), in the space groups Ama2 and P2(1)/c, respectively, have been determined for the first time by single-crystal X-ray diffraction. The structures represent two novel structure types of monovalent ion dimolybdates, A(2)Mo(2)O(7) (A = alkaline elements, NH(4), Ag or Tl). In the structure of Rb(2)Mo(2)O(7), Mo atoms are on a twofold axis, on a mirror plane and in a general position. One of the Rb atoms lies on a twofold axis, while three others are on mirror planes. Two O atoms attached to the Mo atom on a mirror plane are located on the same plane. Rubidium dimolybdate contains a new kind of infinite Mo-O chain formed from linked MoO(4) tetrahedra and MoO(6) octahedra alternating along the a axis, with two terminal MoO(4) tetrahedra sharing corners with each octahedron. The chains stack in the [001] direction to form channels of an approximately square section filled by ten-coordinate Rb ions. Seven- and eight-coordinate Rb atoms are located between chains connected by a c translation. In the structure of Cs(2)Mo(2)O(7), all atoms are in general positions. The MoO(6) octahedra share opposite corners to form separate infinite chains running along the c axis and strengthened by bridging MoO(4) tetrahedra. The same Mo-O polyhedral chain occurs in the structure of Na(2)Mo(2)O(7). Eight- to eleven-coordinate Cs atoms fill the space between the chains. The atomic arrangement of caesium dimolybdate has an orthorhombic pseudosymmetry that suggests a possible phase transition P2(1)/c-->Pbca at elevated temperatures.

New structure type in the morphotropic series of A 2 + M 2 2+ (MoO4)3: crystal structure of Rb2Cu2(MoO4)3

Isostructural compounds A2Cu2(MoO4)3 (A = Rb, Cs) were synthesized. The new structure type of the compounds was established for the rubidium-containing compound as an example (a =27.698,b =5.102,c =19.292 å, Β = 707.26‡,Z = 8, space group C2/c, R = 0.016). The structure is characterized by pairs of infinite wolframite-like ribbons of CuO(4+2) octahedra stretching along [010] and additionally bridged by MoO4 tetrahedra. The tetrahedra located between the ribbons weakly interact with each other at distances Mo-O of 2.545 and 2.853 å. There are four such quasione-dimensional copper-molybdenum-oxygen radicals per unit cell; the radicals are united into a single structure by rubidium ions having coordination numbers (CN) 9 and 10.

Binary molybdates K4M2+(MoO4)3 (M2+=Mg, Mn, Co) and crystal structure of K4Mn(MoO4)3

AbstractBinary molybdates K4M2+ (MoO4)3 (M2+=Mg, Mn, Co) isostructural to triclinic \ga-K4Zn(WO4)3 were synthesized, and optimal conditions for their spontaneous crystallization were found. It was established by XRPA and DTA that at 530°C the structure of the compound with cobalt undergoes a transition to the orthorhombic structure of K4Zn(MoO4)3. The structure of K4Mn(MoO4)3 was determined from single crystal diffraction data (a=7.613, b=9.955, c=10.156 Å,α=92.28,β=106.66,γ=105.58°, Z=2, space group

A morphotropic series of the cluster complexes [Ln(DMF)8][Re6Q7Br7] (Q = S, Se): Synthesis, structure, and thermal transformations

P\bar 1

New triple molybdates Cs3LiCo2-(MoO4)4 and Rb3LiZn2(MoO4)4, filled derivatives of the Cs6Zn5(MoO4)8 type

, R=0.030). In this compound, Mn has a higher coordination number (CN=5+1) than that of Zn inα-K4Zn(WO4)3 (CN=4+1). The main structural feature is pairs of MnO6 octahedra linked by the bridging MoO4 tetrahedra into ribbons stretching along the a axis. The structure is compared with related structures of binary molybdates and other members of the alluaudite family.

Synthesis and crystal structure of new complex oxides K10M2+Mo7O27 (M2+ = Mg, Mn, Co)

Cs2Pb(MoO4)2 crystals were prepared by crystallization from their own melt, and the crystal structure has been studied in detail. At 296 K, the molybdate crystallizes in the low-temperature α-form and has a monoclinic palmierite-related superstructure (space group C2/m, a = 2.13755(13) nm, b = 1.23123(8) nm, c = 1.68024(10) nm, β = 115.037(2)°, Z = 16) possessing the largest unit cell volume, 4.0066(4) nm3, among lead-containing palmierites. The compound undergoes a distortive phase transition at 635 K and incongruently melts at 943 K. The electronic structure of α-Cs2Pb(MoO4)2 was explored by using X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy methods. For α-Cs2Pb(MoO4)2, the photoelectron core-level and valence-band spectra and the XES band representing the energy distribution of Mo 4d and O 2p states were recorded. Our results allow one to conclude that the Mo 4d and O 2p states contribute mainly to the central part and at the top of the valence band, respectively, with also significant contributions throughout the whole valence-band region of the molybdate under consideration.

Structure and properties of Li2Zn2(MoO4)3 crystals activated with copper and chromium ions

The reactions of the octahedral anionic complexes [Re6Q7Br7]3− (Q = S, Se) with lanthanide bromides in DMF were studied. The reactions gave a series of compounds [Ln(DMF)8][Re6Q7Br7] (Q = S, Se) containing [Ln(DMF)8]3+ complex cations. The compounds were studied by single-crystal and powder X-ray diffraction and thermal analyses. The crystal structures of [Ln(DMF)8][Re6S7Br7] with Ln = La (I), Ce (II), Nd (III), Eu (IV), and Lu (V) and [Ln(DMF)8][Re6Se7Br7] with Ln = La (VI), Ce (VII), Pr (VIII), and Lu (IX) were determined. It was found that [Ln(DMF)8][Re6Q7Br7] (Q = S, Se) can be divided into three structural groups: I, II, and VI (type A), VII (type B), and III–V, VIII, IX (type C). The complex [Pr(DMF)8][Re6Se7Br7] was found to crystallize in two polymorphous modifications with type B and C structures. Presumably, the morphotropic transitions in the [Ln(DMF)8][Re6Q7Br7] series (Q = S, Se) are mainly related to the change in the configuration of the [Ln(DMF)8]3+ cations, resulting in a change in the packing motif of large complex ions in the crystals. The compounds [Ln(DMF)8][Re6Se7Br7] decompose according to a stepwise pattern, which suggests an intermediate formation of the complexes [Ln(DMF)6][Re6Se7Br7] (this was proved for Ln = Yb, Lu) with subsequent more extensive transformations, which affect also the cluster anion.

Phase formation in the Ag2MoO4-CuO-MoO3 system and the crystal structure of the new double molybdate Ag2Cu2(MoO4)3

The subsolidus regions of the Li2MoO4-A2+MoO4-NiMoO4 (A+ = K, Rb, Cs) systems at 510°C have been triangulated by the intersecting-joins method. The A2MoO4-Li2Ni2(MoO4)3, Li2MoO4-A2Ni2(MoO4)3, A2Ni2(MoO4)3-Li2Ni2(MoO4)3 (A = K, Rb, Cs), and ALiMoO4-A2Ni2(MoO4)3 (A = K, Rb) joins have been investigated. The subsolidus phase formation study has also been completed by spontaneous flux crystallization. No triple salts have been identified, but only compounds belonging to the boundary binary systems. The crystal structure of Cs2Ni2(MoO4)3 (a = 10.7538 Å, Z = 4, space group P213, R = 0.0082) belonging to the langbeinite type has been determined. It is built of a three-dimensional framework of vertexsharing MoO4 tetrahedra and NiO6 octahedra and cesium ions occupying large out-of-framework cavities. All alkali-metal nickel molybdates are yellow. These compounds are usable as pigments, as judged from their reflection spectra and calculated color characteristics, namely, colorfulness (C), lightness (L), and hue (H).