Title: Electrostatic Interactions versus Second Order Jahn–Teller Distortion as the Source of Structural Diversity in Li ₃ MO ₄ Compounds (M = Ru, Nb, Sb and Ta)

Two compounds of formula La{sub 7}A{sub 3}W{sub 4}O{sub 30} (with A=Nb and Ta) were prepared by solid-state reaction at 1450 and 1490{sup o}C. They crystallize in the rhombohedric space group R-3 (No. 148), with the hexagonal parameters: a=17.0640(2)A, c=6.8859(1)A and a=17.0701(2)A, c=6.8851(1)A. The structure of the materials was analyzed from X-ray, neutron and electronic diffraction. These oxides are isostructural of the reduced molybdenum compound La{sub 7}Mo{sub 7}O{sub 30}, which are formed of perovskite rod along [111]. An order between (Nb, Ta) and W is observed.

Cleavage of C-S bonds or substitution of the RS{sup {minus}} in [Nb{sup V}(S){sub 2}-({sup t}BuS){sub 2}]{sup {minus}} with S{sup 2{minus}} was studied for potential toward synthesis of [NbS{sub 4}]{sup 3{minus}}. The authors describe the synthesis and subsequent X-ray crystal structure of the Et{sub 4}N{sup +} salts of [M{sup V}(E){sub 3}({sup t}BuS)]{sup 2{minus}} (E = Se, M = Nb (III), Ta (IV); E = S, M = Nb (V)).

New substituted copper titanates with the CaCu/sub 3/Ti/sub 4/O/sub 12/ perovskite-like structure were synthesized and characterized. Their formula is Li absolute value of Cu/sub 3-x/Li/sub x/ absolute value of Ti/sub 3-x/M/sub 1 + x//sup V/ O/sub 12/. There is a homogeneity range for M/sup V/ = Nb, 0.12 less than or equal to x less than or equal to 0.33, and a unique composition for M/sup V/ = Ta, x = 0.33. The unit cell is cubic: a approx. 2a/sub p/ (parameter of the ideal cubic cell) approx. 7.40 A. The CaCu/sub 3/Ti/sub 4/O/sub 12/-type structure was confirmed from anmore » X-ray powder structural determination. Lithium occupies both square planar sites where it replaces copper and icosahedral sites, with a probable delocalization. Crystal chemistry of the AC/sub 3/B/sub 4/O/sub 12/ structure is considered, taking into account the evolution of anion packing and the distortion of polyhedra. A diagrammatic representation is proposed so that precise information on the regularity of the C/sub 3/B/sub 4/O/sub 12/ network can be obtained.« less

Hydrothermal reactions of molybdenum-oxide precursors with polyalcohols in the presence of base yielded two series of mixed-valence oxomolybdenum clusters, the hexadecanuclear species [XH{sub 12}(Mo{sup VI}O{sub 3}){sub 4}Mo{sup V}{sub 12}O{sub 40}]{sup m{minus}}(X=Na{sup +}, m=7; X=2H{sup +}, m=6) and the superclusters [XH{sub n}Mo{sup VI}{sub 6}Mo{sup V}{sub 36}O{sub 109}(OCH{sub 2}){sub 3}CR{sub 7}]{sup m{minus}} (X=Na-(H{sub 2}O){sub 3}{sup +}, m=9, n=13; X=Na(H{sub 2}O){sub 3}{sup +}, m=7, n=15; X=MoO{sub 3}, m=9, n=14; X=MoO{sub 3}, m=10, n=13). In a representative synthesis for the hexadencanuclear class of materials, the hydrothermal reaction of a mixture of Na{sub 2}MoO{sub 4}{center_dot}2H{sub 2}O, MoO{sub 3}, Mo metal, and NH{sub 4}Cl produced (NH{submore » 4}){sub 7}[NaMo{sub 16}(OH){sub 12}O{sub 40}]{center_dot}4h{sub 2}O (1{center_dot}4H{sub 2}O) as red-orange crystals. The compound (Me{sub 3}NH){sub 4}K{sub 2}[H{sub 2}Mo{sub 16}(OH){sub 40}]{center_dot}8H{sub 2}O(2{center_dot}8H{sub 2}O(2{center_dot}8H{sub 2}O) was prepared in a similar fashion. The structure of the anion of 1 consists of an {epsilon}-Keggin core H{sub 12}Mo{sub 12}O{sub 40}, capped on four hexagonal faces by MoO{sub 3} units and encapsulating a Na{sup +} cation. The structure of the oxomolybdenum framework of 2 is essentially identical to that of 1; however, the central cavity is now occupied by 2H{sup +}.« less