Symmetry and effective charge distribution in complex compounds of niobium as indicated by x-ray spectra

Barinskii, R. L.; Куликова, И. М.; Lipatova, N.P.

doi:10.1007/bf00746913

Cited by 3 publications

(3 citation statements)

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“…7 The [NbF 6 ] − anion was reported to crystallize with tetraethylammonium (pK a = 11 61 ) in the structure of [(C 2 H 5 ) 4 N]NbF 6 . 62 When an organic base is introduced with a corresponding pK a lower than the pK a of hydrofluoric acid (pK a = 3.17) such as pyrazine and quinoxaline in our experiments, no crystals were obtained, probably because the weak acid HF does not protonate the very weak organic bases. The effect of the temperature can be neglected because the pK a of organic acids had been reported to decrease only slightly with increasing temperature.…”

Section: ■ Experimental Sectionmentioning

confidence: 63%

“…Thus, when py (p K a = 5.23) is introduced into a solution, infinite chains of [NbOF 4 ] − anions will crystallize in I owing to weakly basic solutions ( low fluoride concentration), while when 4,4′-bpy (p K a = 10.5) is introduced into a solution, isolated [NbOF 5 ] 2– anions crystallize in II owing to strong basic solutions ( high fluoride concentration) . The [NbF 6 ] − anion was reported to crystallize with tetraethylammonium (p K a = 11) in the structure of [(C 2 H 5 ) 4 N]NbF 6 . When an organic base is introduced with a corresponding p K a lower than the p K a of hydrofluoric acid (p K a = 3.17) such as pyrazine and quinoxaline in our experiments, no crystals were obtained, probably because the weak acid HF does not protonate the very weak organic bases.…”

Section: Resultsmentioning

confidence: 99%

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From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbO_xF_y]ⁿ⁻ Species

Gautier

Donakowski

et al. 2013

Inorg. Chem.

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In this study, we describe the crystallization of specific niobium oxide-fluoride anions (either [NbOF4](-) or [NbOF5](2-)) by increasing the fluoride concentration with the appropriate use of organic bases with varied corresponding pKa values to create suitable equilibria for the formation of each anion. HpyNbOF4 (I; py = pyridine) contains the [NbOF4](-) anion, while [H2(4,4'-bpy)]NbOF5] (II; 4,4'-bpy = 4,4'-bipyridyl) contains the [NbOF5](2-) anion; their identity is correlated with reagent ratios. The increase of basic species (proton acceptors) results in an increase in the fluoride concentration and high fluoride-containing anions. The crystallization of [NbOF4](-) in [NbO2/2F4]∞ chains in I was controlled with the use of weak base pyridine (pKa = 5.23), while isolated [NbOF5](2-) crystallized in II with strong base 4,4'-bipyridyl (pKa = 10.5). This approach can be broadly applied to target-specific basic building units for fundamentally new and potentially functional solid-state materials.

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Section: ■ Experimental Sectionmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 99%

From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbO_xF_y]ⁿ⁻ Species

Gautier

Donakowski

et al. 2013

Inorg. Chem.

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“…In this study, the [TaOF 5 ] 2– , [TaF 6 ] − , and [TaF 7 ] 2– anions crystallize when the corresponding p K a of introduced organic bases are 4.23, 7.14, 9.98, respectively. Previous studies have shown that the niobium oxide-fluoride and fluoride anions, [NbOF 4 ] − , [NbOF 5 ] 2– , and [NbF 6 ] − crystallize from HF aq solutions when the corresponding p K a of introduced organic molecules are 4.27–7.14, 7.14–11, 11, respectively. ,− In spite of similar chemistry of tantalum and niobium, specific oxide-fluoride/fluoride anions of tantalum and niobium crystallize from solutions at different acidities. For example, the introduction of 1,10-phenanthroline (phen) or 2,2′-bpy with corresponding p K a of ∼4.2 lead to chains of [NbOF 4 ] − for niobium in contrast to the isolated [TaOF 5 ] 2– anions obtained for tantalum.…”

Section: Resultsmentioning

confidence: 99%

Specific Chemistry of the Anions: [TaOF₅]^2–, [TaF₆]⁻, and [TaF₇]^2–

Gautier

Donakowski

et al. 2014

Crystal Growth & Design

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The controlled crystallization of specific tantalum oxide-fluoride and tantalum fluoride anions ([TaOF 5 ] 2− , [TaF 6 ] − , and [TaF 7 ] 2− ) is demonstrated using organic reagents with varied corresponding pK a values in the presence of aqueous hydrofluoric acid. The identity of tantalum oxide-fluoride or fluoride anions of [TaOF 5 ] 2− , [TaF 6 ] − , and [TaF 7 ] 2− are shown to crystallize successively from solution to solid state by increasing the corresponding pK a of organic reagents, which lead to the subsequent increase of fluoride concentration in the hydrofluoric acid solution.With the use of this methodology, three new hybrid crystal structures were targeted: [H 2 (2,2′-bpy)]TaOF 5 (2,2′-bpy = 2,2′-bipyridyl) 1, [Hdpa]TaF 6 (dpa = 2,2′-dipyridylamine) 2, and [H 2 En]TaF 7 (En = ethylenediamine) 3, respectively. The applicability and comparison of this methodology for tantalum and previously prepared niobium compounds show that it can be broadly used to design new materials with specific functionalities for other transition metal oxide-fluorides. ■ INTRODUCTIONHigh second-order nonlinear optical (NLO) response in noncentrosymmetric (NCS) structures often are generated from asymmetric basic building units (BBUs), such as anionic groups with π-orbital systems or stereochemically active lone pairs [(BO 3 ) 3− , (B 3 O 6 ) 3− , (IO 3 ) − , (TeO x ) n− , [AsS 3 ] 3− , [SbS 3 ] 3− , etc.] 1−7 and second-order Jahn−Teller (SOJT) distorted d 0 transition metal centers (Ti 4+ , Nb 5+ , Ta 5+ , Mo 6+ , etc.). 8−12 Materials with potentially higher second-harmonic generation (SHG) efficiencies based on the concept of two combined acentric BBUs have been shown to crystallize in one NCS structure, either by the combination of acentric cations and acentric anions 13−15 or combination of two acentric anions. 8,16−19 Thus, to incorporate specific acentric BBUs into NCS structures, a rational synthetic approach to target the crystallization of specific anions is needed.Tantalum compounds with strong SHG responses have been recently reported. 16 Owing to the good solubility of tantalum oxide in hydrofluoric acid solutions, tantalum oxide-fluoride/ fluoride anions similar to other early transition metal oxidefluoride anions have been extensively examined. 20−23 Previous tantalum compounds with different tantalum oxide-fluoride/ fluoride anions (e.g., [ TaOF 5 ] 2− , 24,25 [Ta(O 2 )F 5 ] 2− , 26,27 [TaF 6 ] − , 28 [TaF 7 ] 2− , 29−33 [Ta 2 OF 10 ] 2− dimer 34 and the adamantine-like cage [Ta 4 O 6 F 12 ] 2− anions 35 ) have been reported for their diverse coordination chemistry and interesting properties. Solution-phase NMR, Raman, and IR spectroscopy at room temperature have shown that different tantalum oxide-fluoride/fluoride species exist in different fluoride concentration conditions. 36−41 However, the controlled crystallization of specific tantalum oxide-fluoride/ fluoride anions has not been studied so far. In this article, to better understand specific chemistry of tantalum and target potential acentric units of ...

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Niobium LIII and LII X-ray absorption-edge spectra of Nb2O5 and NH4NbF6

Sugiura

Kitamura

Muramatsu

1988

Journal of Physics and Chemistry of Solids

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Symmetry and effective charge distribution in complex compounds of niobium as indicated by x-ray spectra

Cited by 3 publications

References 3 publications

From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbO_xF_y]ⁿ⁻ Species

From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbO_xF_y]ⁿ⁻ Species

Specific Chemistry of the Anions: [TaOF₅]^2–, [TaF₆]⁻, and [TaF₇]^2–

Niobium LIII and LII X-ray absorption-edge spectra of Nb2O5 and NH4NbF6

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Symmetry and effective charge distribution in complex compounds of niobium as indicated by x-ray spectra

Cited by 3 publications

References 3 publications

From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbOxFy]n− Species

From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbOxFy]n− Species

Specific Chemistry of the Anions: [TaOF5]2–, [TaF6]−, and [TaF7]2–

Niobium LIII and LII X-ray absorption-edge spectra of Nb2O5 and NH4NbF6

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From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbO_xF_y]ⁿ⁻ Species

From Solution to the Solid State: Control of Niobium Oxide–Fluoride [NbO_xF_y]ⁿ⁻ Species

Specific Chemistry of the Anions: [TaOF₅]^2–, [TaF₆]⁻, and [TaF₇]^2–