Structure des complexes peroxydiques des métaux de transition. III. Structure cristalline du tétraperoxoniobate de potassium et de magnésium à sept molécules d'eau, KMgNb(O2)4.7H2O

Abstract

The crystal structure of potassium magnesium tetraperoxoniobate KMgNb(O2) 4. 7H20 has been determined by X-ray diffraction. Crystals are monoclinic with a = 11-95 _+ 0.01, b = 12.19 + 0.01, c = 14.08 + 0.01 A; t= 141.2+ 0.1°; Z= 4; space group P21/c. Mg(H20) 2+ cations are disposed in layers which are parallel to the (100) plane. The non-bonded water molecules and the K + and NbOs a-ions are disposed between these layers. The Nb(Oz)]-ion has nearly D2a symmetry. The O-O mean distance is 1.50 A.

Homo- and Heterobimetallic Niobiumv and Tantalumv Peroxo-tartrate Complexes and Their Use as Molecular Precursors for Nb−Ta Mixed Oxides

“…Niobium and tantalum exhibit an 8-fold coordination by oxygen atoms belonging to two bidentate peroxides, two monodentate carboxylato, and two alkoxo groups from both bridging tartrato ligands. The coordination polyhedron observed in both cases is a dodecahedron, as already observed in all Nb or Ta peroxo compounds described so far in the literature. ,,− In crystal 1b , the coordination distances are in the range of the values already reported for Nb peroxo complexes. ,− The Nb−O(carboxylato) distances are 2.134(3) and 2.135(3) Å, while the Nb−O(alkoxo) bond distances reach 2.014(3) and 2.181(3) Å. The Nb−O(peroxo) bond lengths range from 1.992(3) to 2.002(3) Å with a mean value of 1.997(3) Å, and the (O−O) distances reach 1.493(4) and 1.500(4) Å.…”

“…The coordination polyhedron observed in both cases is a dodecahedron, as already observed in all Nb or Ta peroxo compounds described so far in the literature. 27,28,[31][32][33][34][35][36][37] In crystal 1b, the coordination distances are in the range of the values already reported for Nb peroxo complexes. 27,[31][32][33][34][35][36] The Nb-O(carboxylato) distances are 2.134(3) and 2.135(3) Å, while the Nb-O(alkoxo) bond distances reach 2.014(3) and 2.181(3) Å.…”

“…27,28,[31][32][33][34][35][36][37] In crystal 1b, the coordination distances are in the range of the values already reported for Nb peroxo complexes. 27,[31][32][33][34][35][36] The Nb-O(carboxylato) distances are 2.134(3) and 2.135(3) Å, while the Nb-O(alkoxo) bond distances reach 2.014(3) and 2.181(3) Å. The Nb-O(peroxo) bond lengths range from 1.992(3) to 2.002(3) Å with a mean value of 1.997(3) Å, and the (O-O) distances reach 1.493(4) and 1.500(4) Å.…”

Reactions of Lanthanides and Actinides in Molten Alkali Metal/Polychalcogenide Fluxes at Intermediate Temperatures (250−600 °C)

“…Second, the presence of the Se−Se bonds, although slightly elongated (2.38 and 2.40 Å), necessitates that the corresponding Se−U−Se angle be smaller than in an ideal dodecahedron (Se(1)−U−Se(2) angle 49.05°; corresponding ideal dodecahedron angle 73.69°). Although without precedent in metal−chalcogenide systems, [USe 8 ] 4- is isostructural (but not isoelectronic) with the known peroxo anions ([M(O 2 ) 4 ] n - ) (M = Cr 5+ , V 5+ , Nb 5+ , Ta 5+ , Mo 6+ , W 6+ ).

1 Two views of the structure of the [U(Se 2 ) 4 ] 4- anion.

…”

Synthesis, Solution and Solid State Structures, and Aqueous Chemistry of an Unstable Polyperoxo Polyoxometalate: [P2W12(NbO2)6O56]12-

“…This η 2 -peroxo-containing distorted pentagonal bipyramidal coordination polyhedron is seen for the metal centers in only one other conventional (highly condensed) polyoxoanion, the β 3 -[(Co II O 4 )W 11 O 31 (O 2 ) 4 ] 10- complex of Baker and co-workers. , None of the other structurally characterized polyperoxotungstates or polyperoxomolybdates have a conventional polyoxometalate structure. , The average O p −O p distance in 1 (1.43 Å) is slightly shorter than that for noncoordinated O 2 2- (1.49 Å) and is mainly attributed to the decrease in repulsion between the lone electron pairs on each oxygen in O 2 2- . The average Nb−O p distance of 1.93 Å is 0.1 Å shorter than that in the monomeric tetraperoxo niobium complex, [Nb(O 2 ) 4 ] 3- , , while the average O p −Nb−O p angle of 43.7° is close to that in [Nb(O 2 ) 4 ] 3- (43.3°). The relative orientations of the NbO 2 units at the belt positions is noteworthy; two of them (Nb8,O19,O20 and Nb14,O51,O52) lie in the plane defined by the W 4 Nb 2 belts, while the other two (Nb9,O21,O22 and Nb15,O53,O54) lie perpendicular.…”