• Journal of Electrochemical Science and Technology
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• v.14 no.2
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• pp.152-161
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• 2023

Vanadium redox flow batteries (VRFBs) have been considered one of promising power sources for large scale energy storage systems (ESS) because of their excellent cycle performance and good safety. However, VRFBs still have a few challenging issues, such as poor Coulombic efficiency due to vanadium crossover between catholyte and anolyte, although recent efforts have shown promise in electrochemical performance. Herein, the vanadium complexes with various glyme ligands have been examined as active materials to suppress vanadium crossover between catholyte and anolyte, thus improving the Coulombic efficiency of VRFBs. The conventional Nafion membrane has a channel size of ca. 10 Å, whereas vanadium cation species are small compared to the Nafion membrane channel. For this reason, vanadium cations can permeate through the Nafion membrane, resulting in significant vanadium crossover during cycling, although the Nafion membrane is a kind of ion-selective membrane. In this regard, various glyme additives, such as 1,2-dimethoxyethane (monoglyme), diethylene glycol dimethyl ether (diglyme), and tetraethylene glycol dimethyl ether (tetraglyme) have been examined as complexing agents for vanadium cations to increase the size of vanadium-ligand complexes in electrolytes. Since the size of vanadium-glyme complexes is proportional to the chain length of glymes, the vanadium permeability of the Nafion membrane decreases with increasing the chain length of glymes. As a result, the vanadium complexes with tetraglyme shows the excellent electrochemical performance of VRFBs, such as stable capacity retention (90.4% after 100 cycles) and high Coulombic efficiency (98.2% over 100 cycles).

• Bulletin of the Korean Chemical Society
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• v.7 no.1
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• pp.15-20
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• 1986

Modified technique in calculating the dipole moments for square pyramidal complexes has been developed and then the dipole moments for bisacetylacetonato(oxo)vanadium(Ⅳ) complexes are calculated, adopting this approach. The calculated dipole moments for bisacetylacetonato(oxo)vanadium(Ⅳ) in benzene and bisacetylacetonato(oxo)vanadium in dioxane solutions are in agreement with the observed values. The calculated dipole moments of bisacetylacetonato(oxo)vanadium(Ⅳ) in dioxane solution is slightly higher than that of bisacetylacetonato(oxo)vanadium(Ⅳ) in benzene. Such a result may suggest that bisacetylacetonato(oxo)vanadium(Ⅳ) interact with dioxane molecule to form bisacetylacetonato(oxo)vanadium(Ⅳ)-dioxane adduct. This calculated dipole moments are also in agreement with the experimental results.

• Journal of the Korean Chemical Society
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• v.8 no.4
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• pp.147-152
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• 1964

Vanadium (IV) and vanadium (V) cupferrate compositions in benzene phase were determined by molar ratio method and continuous variation method spectrophotometrically at 450$m{\mu}$ or 445$m{\mu}$ of wavelength. Compositions of vanadium (IV) cupferrates, V(IV)/Cupf, varied from 1/2 to 1/4 with the acidity of solution from which the complexes were precipitated. The complexes precipitated were vanadium(IV) cupferrate($VCupf_4$) in solution with lower pH than 1.0, and vanadyl(IV) cupferrate ($VOCupf_2$) in solution with 1.8-4.3 of pH. It was considered, however, that the complexes in solution with 1.3-1.7 of pH might be hydrogen vanadyl(IV) cupferrate ($HVOCupf_3$) or nearly equimolar mixture of $VCupf_4\;and\;VOCupf_2$ complexes. Vanadium (V) cupferrate composition did not vary with the acidity of solution from which the complexes were precipitated. In solution with lower pH than 1.8, the complex precipitated was hydrogen vanadyl (V) cupferrate, $HVO_2Cupf_2$.

• Journal of the Korean Magnetic Resonance Society
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• v.1 no.1
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• pp.1-6
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• 1997

Several dioxovanadate (V) complexes are synthesized and studied by solution and solid-state 51V NMR spectroscopy. In the results, large 51V chemical shift anisotropy ({{{{ DELTA delta }}a = -800 ∼720 ppm) and quadrupole coupling (e2q /h = 7.50 ∼ 9.16 MHz) were observed in the solid-state complexes. The isotropic chemical shifts of the solid samples are very close to the values obtained from solution measurements.

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.33-38
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• 2005

The distribution of vanadium and iron ionic species in the presence of picolinate ligand has been simulated at various conditions with different pH values and compositions in the decontamination waste solution. In spite of variations of metal concentration in the decontamination solution, the shape of distribution diagrams were not changed greatly at both high (the molar ratio of picolinate to vanadium is 6) and low (the molar ratio is 3) LOMI decontamination conditions. However, in the solution of low-picolinate condition the shape of the distribution diagram of iron(II)-picolinate complexes was changed significantly. This phenomenon is attributed to the shortage of relative amount of picolinate ligand to iron existed in the solution, and originated from the difference in stability constants for complexes formed between vanadium(III) and iron(II) species with picolinate ligand. The distribution diagrams obtained in this study can be applied very usefully to the prediction or understanding the reaction phenomena occurred at various conditions in the course of the LOMI waste treatments such as an ion exchange operation.

• Bulletin of the Korean Chemical Society
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• v.14 no.5
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• pp.557-561
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• 1993

The interaction of vanadium(V) with various a-hydroxycarboxylate ligands in aqueous solution at pH 3.2 have been studied by $^{51}V$ and $^{13}C$ NMR spectroscopies. From the results it is supposed that vanadates mainly form the octahedral complexes with lactate, 2-hydroxybutyrate, glycerate, and malate. While, vanadates form the trigonal-bipyramidal complexes with glycolate, tartarate, and 2-hydroxy-3-methylbutyrate, and tetrahedral complexes with pyruvate(diol), 2-hydroxyisobutyrate, and 2-hydroxy-3-methylbutyrate. The bipyramidal products are formed as monomeric compounds. The octahedral products are formed as dimeric compounds with no evidence for a significant proportion of the monomeric derivatives. The complexes are mainly formed through the coordination at the carboxylate and the 2-hydroxyl groups of the ligands.

• Bulletin of the Korean Chemical Society
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• v.24 no.7
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• pp.1014-1016
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• 2003

• Journal of the Korean Chemical Society
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• v.45 no.3
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• pp.213-218
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• 2001

The reaction of peroxo vanadium(V) complexes, $VO(O_2)_2(pic)^{2-}$, $VO(O_2)(nta)^{2-}$, and $VO(O_2)(dipic)^-$ with thiolato-cobalt(III), $(en)_2Co(SCH_2CH_2NH_2)^{2+}$ resulted in an oxygen-atom transfer in aqueous solutions. Rate constants ($M^{-1}S^{-1}$) for these reactions were (35$\pm$1), $(4.8{\pm}0.4){\times}10^{-2}$ , and $(8.6{\pm}0.5){\times}10^{-4}$, respectively. The coordinate peroxide was activated in the oxygen-atom-transfer reaction of $VO(O_2)_2(pic)^{2-}$, but it is not the case for VO(O$_2$) $(nta)^{2-}$ and VO(O$_2$) $(dipic)^-$. In this paper, we proposed that the direct attack of an electrophilic peroxide to a nucleophilic substrate occurs in the oxygen-atom transfer pathway of peroxo vanadium(V) complexes.

• Bulletin of the Korean Chemical Society
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• v.13 no.1
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• pp.22-26
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• 1992

The solution structures of the vanadium(V) complexes of iminodiacetate analogues, such as iminodiacetate (IDA), methyliminodiacetate (MeIDA), ethyliminodiacetate (EtIDA), benzyliminodiacetate (BzIDA), pyridine-2,6-dicarboxylate (DPA), and 2-hydroxyethyliminodiacetate (HEIDA), have been studied by $^{13}C-$ and $^{51}V$-NMR spectroscopy. Assuming that the complexes have a $cis-VO_2$ core, IDA, MeIDA, EtIDA, and BzIDA act as facial tridentate ligands to form octahedral complexes, whereas DPA coordinates to $VO_2^+$ as a meridional tridentate. And one water molecule fulfills the remaining site to satisfy the coordination number of six. But HEIDA coordinates to $VO_2^+$ through one IDA moiety and one hydroxyl group, acting as a tetradenate.

• Journal of Photoscience
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• v.9 no.2
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• pp.412-414
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• 2002

Several peroxovanadium(V) complexes with an organic chelate ligand decompose spontaneously, depending on the nature of the chelate ligand. The self-decomposition reactions of the dinuclear peroxovanadium(V) complex with 2-oxo-l,3-diaminopropane-N,N,N',N'-tetraacetate (dpot) and the peroxovanadium(V) complexes with N-carboxymethylhistidinate (cmhist) and histamine-N,N-diacetate (histada) accompany the reduction of vanadium(V) to vanadium(IV). This implies that the peroxide anion acts as a reducing agent and thus the peroxide is oxidized in the decomposition process of the peroxovanadium(V) complexes. The oxidized dioxygen species have been characterized spectrophotometrically. Superoxide anion has been detected in 2-3 % yields using the reduction of cytochrome c method and chemiluminescence method utilized MCLA as a fluorescer. Singlet oxygen has also been detected in higher yields on the basis of chemiluminescence of tryptophan.