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

Polyoxoanions assembled by the condensation of vanadate, tungstate and selenite: solution studies and crystal structures of the mixed metal derivatives (NMe 4_{4}) 2_{2} Na 2_{2} [WVI^{VI} 4_{4} V V^{V} 2_{2} O 19_{19} ]·8H2_{2}O and (NMe4_{4} )4.83_{4.83} [(SeIV^{IV}WVI^{VI}4.57_{4.57} VV^{V}4.43_{4.43}O33_{33})2_{2} (WVI^{VI}(O)(H2_{2}O))(V V^{V}O) 2.6_{2.6} ]·10.57H2_{2}O

The reaction of acidified aqueous solutions of Na2WO4, NaVO3 and SeO2 in a 16 : 4 : 3 molar ratio gives a complex mixture of polyoxometalates (POMs) with both WVI and VV addenda, formulated as [(SeIVWVIxVV9−xO33)2(WVIO(H2O))(VO)m]n− with x = 4, 5, 6; m = 2 or 3. In solution, the sandwich-type complexes [(SeIVWVIxVV9−xO33)2(WVIO(H2O))(VO)m]n− slowly lose Se and convert into [WVI4VV2O19]4− and further to [WVI5VVO19]3− with a Lindqvist-type structure. These transformations were monitored with 51V and 77Se NMR, electrospray mass-spectrometry and capillary electrophoresis. Crystals of (NMe4)2Na2[(W4V2)O19]·8H2O (1) and (NMe4)4.83[(SeW4.57V4.43O33)2(W(O)(H2O))(VO)2.6]·10.57H2O (2) were isolated and structurally characterized

Possibilities of Mechanochemical Synthesis of Apatites with Different Ca/P Ratios

Apatite is widely used in medicine as a biomaterial for bone tissue restoration. Properties of apatite depend on its composition, including the Ca/P ratio. This paper shows what range of Ca/P ratio can be attained in apatite by the mechanochemical method of synthesis, providing fast formation of a single-phase product. The synthesis was carried out from a reaction mixture of CaHPO4 and CaO at different Ca/P ratios in the range of 1.17–2.10. The products were studied by PXRD, FTIR and NMR spectroscopy, HRTEM, and STA. In mixtures with a low initial Ca/P ratio (1.17–1.48), directly in the mill, the formation of calcium orthophosphate with whitlockite structure containing an HPO42− group and structural water is shown for the first time. This phosphate has structure similar to that of whitlockites of hydrothermal origin and differs from high-temperature β-tricalcium phosphate that has composition Ca3(PO4)3. A series of samples of apatite was obtained with varied composition, which depends on the initial Ca/P ratio. At Ca/P 1.67, the existence of two types of calcium-rich apatite is confirmed

Possibilities of Mechanochemical Synthesis of Apatites with Different Ca/P Ratios

Apatite is widely used in medicine as a biomaterial for bone tissue restoration. Properties of apatite depend on its composition, including the Ca/P ratio. This paper shows what range of Ca/P ratio can be attained in apatite by the mechanochemical method of synthesis, providing fast formation of a single-phase product. The synthesis was carried out from a reaction mixture of CaHPO4 and CaO at different Ca/P ratios in the range of 1.17–2.10. The products were studied by PXRD, FTIR and NMR spectroscopy, HRTEM, and STA. In mixtures with a low initial Ca/P ratio (1.17–1.48), directly in the mill, the formation of calcium orthophosphate with whitlockite structure containing an HPO42− group and structural water is shown for the first time. This phosphate has structure similar to that of whitlockites of hydrothermal origin and differs from high-temperature β-tricalcium phosphate that has composition Ca3(PO4)3. A series of samples of apatite was obtained with varied composition, which depends on the initial Ca/P ratio. At Ca/P < 1.67, the formation of two types of calcium-deficient apatite was documented. At Ca/P > 1.67, the existence of two types of calcium-rich apatite is confirmed

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

New {RuNO} Polyoxometalate [PW11O39RuII(NO)]4-: Synthesis and Reactivity

New Ru-containing polyoxometalate [PW11O39RuII(NO)]4- (14-) was obtained in high yield by reaction of [Ru(NO)Cl5]2- with [PW11O39]7- and characterized by multinuclear NMR, cyclic voltammetry, IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The intrinsic reactivity of the {RuNO} site in 14- toward various reagents has been studied using a versatile and simple ESI tandem mass spectrometric methodology for identification of the L attached at the Ru site; this approach relies on the preferential liberation of the L ligands attached at the Ru sites upon mass-selecting desired intermediates and subsequent promotion of their fragmentation. Reactions with both hydrazine and hydroxylamine lead to elimination of the nitroso group and quantitative formation of [PW11O39RuIII(H2O)]4- (24-) in aqueous solution. In the reaction with hydroxylamine, an intermediate with coordinated dinitrogen has been detected. An easy access to the NH3-coordinated [PW11O39RuNH3]4- (34-) complex was achieved upon reduction of 14- with Sn2+ in water

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