15 research outputs found
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
Anomalous Behavior of Heat Capacity in Ni2(bdc)2(dabco). Schottky Anomaly and SpinPhonon Interaction
Polyoxoanions assembled by the condensation of vanadate, tungstate and selenite: solution studies and crystal structures of the mixed metal derivatives (NMe ) Na [W V O ]·8HO and (NMe ) [(SeW VO) (W(O)(HO))(V O) ]·10.57HO
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 {Se<sub>2</sub>W<sub>12</sub>} Units
The reaction of Na<sub>2</sub>WO<sub>4</sub> and SeO<sub>2</sub> under moderately acidic conditions yielded
a novel 39-tungsto-6-selenite, [(Se<sub>2</sub>W<sub>12</sub>O<sub>46</sub>(WOÂ(H<sub>2</sub>O))<sub>3</sub>]<sup>24–</sup> (<b>1</b>), isolated as Na<sub>24</sub>[H<sub>6</sub>Se<sub>6</sub>W<sub>39</sub>O<sub>144</sub>]·74H<sub>2</sub>O. The macrocyclic
polyanion consists of three {Se<sub>2</sub>W<sub>12</sub>} fragments
connected via three <i>trans</i>-{WOÂ(H<sub>2</sub>O)}<sup>4+</sup> groups. The same {Se<sub>2</sub>W<sub>12</sub>} building
block is present in the structure of [(Se<sub>2</sub>W<sub>12</sub>O<sub>46</sub>)<sub>2</sub>{Mn<sub>2</sub>ClÂ(H<sub>2</sub>O)<sub>2</sub>}Â{MnÂ(H<sub>2</sub>O)<sub>2</sub>}<sub>2</sub>(SeO)<sub>2</sub>]<sup>13–</sup> (<b>2</b>), which was obtained from
the same reagents in the presence of MnCl<sub>2</sub>. The compounds
were characterized by single-crystal X-ray diffraction, <sup>77</sup>Se NMR, Fourier transform infrared, and Raman spectroscopy
Cyclic Tungstoselenites Based on {Se<sub>2</sub>W<sub>12</sub>} Units
The reaction of Na<sub>2</sub>WO<sub>4</sub> and SeO<sub>2</sub> under moderately acidic conditions yielded
a novel 39-tungsto-6-selenite, [(Se<sub>2</sub>W<sub>12</sub>O<sub>46</sub>(WOÂ(H<sub>2</sub>O))<sub>3</sub>]<sup>24–</sup> (<b>1</b>), isolated as Na<sub>24</sub>[H<sub>6</sub>Se<sub>6</sub>W<sub>39</sub>O<sub>144</sub>]·74H<sub>2</sub>O. The macrocyclic
polyanion consists of three {Se<sub>2</sub>W<sub>12</sub>} fragments
connected via three <i>trans</i>-{WOÂ(H<sub>2</sub>O)}<sup>4+</sup> groups. The same {Se<sub>2</sub>W<sub>12</sub>} building
block is present in the structure of [(Se<sub>2</sub>W<sub>12</sub>O<sub>46</sub>)<sub>2</sub>{Mn<sub>2</sub>ClÂ(H<sub>2</sub>O)<sub>2</sub>}Â{MnÂ(H<sub>2</sub>O)<sub>2</sub>}<sub>2</sub>(SeO)<sub>2</sub>]<sup>13–</sup> (<b>2</b>), which was obtained from
the same reagents in the presence of MnCl<sub>2</sub>. The compounds
were characterized by single-crystal X-ray diffraction, <sup>77</sup>Se 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)TeNb<sub>5</sub>O<sub>18</sub>]<sup>6–</sup> in Water Solution, Comparison with [Nb<sub>6</sub>O<sub>19</sub>]<sup>8–</sup>
Reaction
of [Nb<sub>6</sub>O<sub>19</sub>]<sup>8–</sup> with
H<sub>6</sub>TeO<sub>6</sub> in water gives telluropentaniobate [(OH)ÂTeÂNb<sub>5</sub>O<sub>18</sub>]<sup>6–</sup> (<b>1</b>) as single
product, which was isolated as Na<sup>+</sup> and mixed Na<sup>+</sup>/K<sup>+</sup> salts. Crystal structures were determined for Na<sub>6</sub>[(OH)ÂTeNb<sub>5</sub>O<sub>18</sub>]·15H<sub>2</sub>O (<b>Na</b><sub><b>6</b></sub><b>-1</b>) and K<sub>6</sub>NaÂ[Nb<sub>5.5</sub>Â{TeÂ(OH)}<sub>0.5</sub>O<sub>18.5</sub>]·26H<sub>2</sub>O (<b>K</b><sub><b>6</b></sub><b>Na-1</b>). Formation of <b>1</b> was monitored with electrospray
ionization mass spectrometry (ESI-MS) and <sup>125</sup>Te NMR techniques.
Capillary electrophoresis was used to calculate electrophoretic mobilities
and radii of the anionic species in solutions of [(OH)ÂTeÂNb<sub>5</sub>O<sub>18</sub>]<sup>6–</sup> and [Nb<sub>6</sub>O<sub>19</sub>]<sup>8–</sup> in borate buffer. No condensation or
degradation products were detected. Reactions of <b>1</b> with
{Cp*Rh}<sup>2+</sup> sources gives 1:1 and 2:1 hybrid polyoxometalate,
which are present in solution as a mixture of isomers, as detected
by <sup>125</sup>Te NMR. The isomerism is related to various possibilities
of coordination of {Cp*Rh}<sup>2+</sup> to different {M<sub>3</sub>O<sub>3</sub>} 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 Na<sub>3</sub>[{Cp*Rh}<sub>2</sub>ÂTeNb<sub>5</sub>O<sub>19</sub>]·24H<sub>2</sub>O (<b>Cp*</b><sub><b>2</b></sub><b>Rh</b><sub><b>2</b></sub><b>-1</b>) with two {Cp*Rh}<sup>2+</sup> fragments capping the opposing faces of the Lindqvist anion