Cation-Dependent Self-assembly of Vanadium Polyoxoniobates

Reaction of Na7H[Nb6O19]·15H2O with NaVO3·2H2O at 220 °C in the presence of NaHCO3 gives new bicapped α-Keggin vanadododecaniobate [VNb12O40{NbO(CO3)}2]13–, isolated and structurally characterized as Na9H4[VNb12O40{NbO(CO3)}2]·37H2O (1). According to 51V NMR and ESI-MS data, this anion equilibrates in solution with [VNb12O40]15– and oligomeric species that result from dissociation of the {NbO(CO3)}+ fragments. In the presence of potassium, the same reaction gives [VxNb24O76]n− (x = 4, n = 12 (2a); x = 3, n = 17 (2b)). The anions with x = 3 and 4 cocrystallize together, but exist as separate entities both in solid and in solution according to 51V MAS NMR and ESI-MS data

PFS/Mars Express first results: water vapour and carbon monoxide global distribution

International audienc

PFS/Mars Express first results: water vapour and carbon monoxide global distribution

International audienc

PFS/Mars Express first results: water vapour and carbon monoxide global distribution

International audienc

Cyclic Tungstoselenites Based on {Se₂W₁₂} Units

The reaction of Na₂WO₄ and SeO₂ under moderately acidic conditions yielded a novel 39-tungsto-6-selenite, [(Se₂W₁₂O₄₆(WO­(H₂O))₃]^24– (<b>1</b>), isolated as Na₂₄[H₆Se₆W₃₉O₁₄₄]·74H₂O. The macrocyclic polyanion consists of three {Se₂W₁₂} fragments connected via three <i>trans</i>-{WO­(H₂O)}⁴⁺ groups. The same {Se₂W₁₂} building block is present in the structure of [(Se₂W₁₂O₄₆)₂{Mn₂Cl­(H₂O)₂}­{Mn­(H₂O)₂}₂(SeO)₂]^13– (<b>2</b>), which was obtained from the same reagents in the presence of MnCl₂. The compounds were characterized by single-crystal X-ray diffraction, ⁷⁷Se NMR, Fourier transform infrared, and Raman spectroscopy

Cyclic Tungstoselenites Based on {Se₂W₁₂} Units

The reaction of Na₂WO₄ and SeO₂ under moderately acidic conditions yielded a novel 39-tungsto-6-selenite, [(Se₂W₁₂O₄₆(WO­(H₂O))₃]^24– (<b>1</b>), isolated as Na₂₄[H₆Se₆W₃₉O₁₄₄]·74H₂O. The macrocyclic polyanion consists of three {Se₂W₁₂} fragments connected via three <i>trans</i>-{WO­(H₂O)}⁴⁺ groups. The same {Se₂W₁₂} building block is present in the structure of [(Se₂W₁₂O₄₆)₂{Mn₂Cl­(H₂O)₂}­{Mn­(H₂O)₂}₂(SeO)₂]^13– (<b>2</b>), which was obtained from the same reagents in the presence of MnCl₂. The compounds were characterized by single-crystal X-ray diffraction, ⁷⁷Se NMR, Fourier transform infrared, and Raman spectroscopy

Synthesis and Characterization of [(OH)TeNb₅O₁₈]^6– in Water Solution, Comparison with [Nb₆O₁₉]^8–

Reaction of [Nb₆O₁₉]^8– with H₆TeO₆ in water gives telluropentaniobate [(OH)­Te­Nb₅O₁₈]^6– (<b>1</b>) as single product, which was isolated as Na⁺ and mixed Na⁺/K⁺ salts. Crystal structures were determined for Na₆[(OH)­TeNb₅O₁₈]·15H₂O (<b>Na</b>_<b>6</b><b>-1</b>) and K₆Na­[Nb_5.5­{Te­(OH)}_0.5O_18.5]·26H₂O (<b>K</b>_<b>6</b><b>Na-1</b>). Formation of <b>1</b> was monitored with electrospray ionization mass spectrometry (ESI-MS) and ¹²⁵Te NMR techniques. Capillary electrophoresis was used to calculate electrophoretic mobilities and radii of the anionic species in solutions of [(OH)­Te­Nb₅O₁₈]^6– and [Nb₆O₁₉]^8– in borate buffer. No condensation or degradation products were detected. Reactions of <b>1</b> with {Cp*Rh}²⁺ sources gives 1:1 and 2:1 hybrid polyoxometalate, which are present in solution as a mixture of isomers, as detected by ¹²⁵Te NMR. The isomerism is related to various possibilities of coordination of {Cp*Rh}²⁺ to different {M₃O₃} faces, relative to the unique Te atom. According to ESI-MS experiments in water and methanol, rapid redistribution of the organometallic fragments between the 1:1 and 2:1 complexes takes place. The 1:1 complexes are more stable in water, while 2:1 complexes dominate in methanol. X-ray structural analysis of the crystals isolated from 2:1 reaction mixture allowed identification of Na₃[{Cp*Rh}₂­TeNb₅O₁₉]·24H₂O (<b>Cp*</b>_<b>2</b><b>Rh</b>_<b>2</b><b>-1</b>) with two {Cp*Rh}²⁺ fragments capping the opposing faces of the Lindqvist anion

Native Gold and Unique Gold–Brannerite Nuggets from the Placer of the Kamenny Stream, Ozerninsky Ore Cluster (Western Transbakalia, Russia) and Possible Sources

We carried out a comprehensive study of native gold (morphology, composition, intergrowths, and microinclusions) from alluvial deposits of the Kamenny stream (Ozerninsky ore cluster, Western Transbaikalia, Russia). The study showed that there were four types of native gold, which differed significantly in their characteristics and probably had different primary sources from which placers were formed: gold–quartz, oxidized gold–sulfide, gold–silver, and zones of listvenites with copper–gold and gold–brannerite (Elkon-type). Particular attention was paid to the study of unique, both in size and in composition, gold–brannerite nuggets of the Kamenny stream. It was established that the gold in the gold–brannerite nuggets (GBNs) had wide variations in chemical composition and mineral features. According to them, there were five different fineness types of native gold: 750–800‰; 850–880‰; 880–920‰; 930–960‰; and 980–1000‰. The data obtained indicated a multistage, possibly polygenic, and probably polychronous formation of GBN gold–uranium mineralization. The first stage was the formation of early quartz–nasturanium–gold–W–rutile–magnetite association (Middle–Late Paleozoic age). The second was the crystallization of brannerite and the replacement of an earlier pitchblende with brannerite (Late Triassic (T3)–Early Jurassic (J1) age). The third was the formation of the hematite–barite–rutile–gold association as a result of deformation–hydrothermal processes, which was associated with the appearance of zones of alteration in brannerite in contact with native gold with 8–15 wt.% Ag. The fourth was hypergene or the low-temperature hydrothermal alteration of minerals of early stages with the development of iron hydroxides (goethite) with impurities of manganese, tellurium, arsenic, phosphorus, and other elements. The carbon isotopic composition of an organic substance indicates the involvement of a biogenic carbon source. In the OOC area, there were signs that the composition of the GBNs and the quartz–chlorite–K–feldspar-containing rocks corresponded to Elkon-type deposits

Cd²⁺ Complexation with P(CH₂OH)₃, OP(CH₂OH)₃, and (HOCH₂)₂PO₂^–: Coordination in Solution and Coordination Polymers

The coordination of Cd²⁺ with P­(CH₂OH)₃ (THP) in methanol was followed by ³¹P and ¹¹¹Cd NMR techniques. A cadmium-to-phosphine coordination ratio of 1:3 has been established, and effective kinetic parameters have been calculated. Air oxidation of THP in the presence of CdCl₂ at room temperature produces coordination polymer ³_∞[Cd₃Cl₆(OP­(CH₂OH)₃)₂] (<b>1</b>). The same oxidation reaction at 70 °C gives another coordination polymer, _∞[CdCl₂(OP­(CH₂OH)₃)] (<b>2</b>). Complexes <b>1</b> and <b>2</b> are the first structurally characterized complexes featuring OP­(CH₂OH)₃ as a ligand that acts as a linker between Cd atoms. The addition of NaBPh₄ to the reaction mixture gives coordination polymer _∞[Na₂CdCl₂(O₂P­(CH₂OH)₂)₂(H₂O)₃] (<b>3</b>) with (HOCH₂)₂PO₂^– as the ligand. Coordination polymers <b>1</b>–<b>3</b> have been characterized by X-ray analysis, elemental analysis, and IR spectroscopy