• Bulletin of the Korean Chemical Society
• /
• 제8권1호
• /
• pp.1-3
• /
• 1987

The crystal structure of $K_5Na_2[SbW_6O_{24}]{\cdot}12H_2O$ has been determined. Final R = 0.081 for 890 observed independent reflections collected by diffractometry. Crystal data as follows; trigonal, space group R3m, a = 9.794(1) ${\AA},\;{\alpha}$ = 84.72$(1)^{\circ}$, Z = 1. The heteropolyanion has a structure with point symmetry $D_{3d}$ (3m), of the ideal Anderson-type heteropolyanion. The Sb-W and W-W distances are 3.259(2) and 3.259(3) ${\AA}$. Three types of W-O ($W-O_t,\;W-O_b\;and\;W-O_c$) distances are 1.73(2), 1.95(4) and 2.20(3) ${\AA}$. The Sb-O distance is 1.97(3) ${\AA}$.

• Bulletin of the Korean Chemical Society
• /
• 제34권1호
• /
• pp.225-230
• /
• 2013

A new heteropolyanion-based ionic ($[Hmim]_5PMo_{10}V_2O_{40}$) was synthesized by the reaction of molybdovanadophosphoric acid ($H_5PMo_{10}O_{40}$) with N-methylimidazole. [$[Hmim]_5PMo_{10}V_2O_{40}$ showed a high catalytic activity in the oxidative desulfurization of sulfur-containing compounds in 1-methylimidazolium tetrafluoroborate ($[Hmim]BF_4$) ionic liquid using 30% aqueous $H_2O_2$ as the oxidant. The catalytic system was of high activity, simplified workup and flexible recyclability. The catalytic oxidation reactivity of sulfur-containing compounds decreased in the order dibenzothiophene (DBT) > 4,6-dimethyldibenzothiophene (4,6-DMDBT) > benzothiophene (BT). The influences of various parameters including reaction time (t) and temperature (T), catalyst dosage, and oxidant to sulfur molar ratio n(O)/n(S) on the desulfurization of model oil were investigated in details. 99.1% of DBT conversion in the model oil was achieved at atmospheric pressure under the optimal conditions: n(O)/n(S) = 4:1, $60^{\circ}C$, 100 min and molar ratio of catalyst to sulfur of 0.062. The ionic liquid can be recycled six times without significant decrease in activity.

• 펄프종이기술
• /
• 제37권5호통권113호
• /
• pp.56-62
• /
• 2005

The catalytic effect of molybdovandophosphate heteropolyanion (HPAs) on the delignification of kraft bagasse pulp by hydrogen peroxide has been investigated. Very small amounts of the catalyst (0.05 0.3 mM/l) gave convenient results. Partial reduction of the catalyst was also studied. The effect of reaction medium (water, ethyl alcohol and acetone) on the bleaching was also studied. The results obtained show that the optimum condition for bleaching in presence of polyoxometalate were 0.05 mM/l catalyst concentration at $70^{\circ}C$ reaction temperature and $7\%$ consistency at pH 2 in aqueous medium. The ratio of water to solvent of 60:40 from acetone gives higher brightness than ethyl alcohol. The catalyst solution can be reused for 5 times without any reduction in brightness. ESR for the blank and exhausted solutions under different conditions was also carried out to find the relation between reduced metals and pulp brightness.

• Bulletin of the Korean Chemical Society
• /
• 제16권12호
• /
• pp.1176-1179
• /
• 1995

1H NMR spectra of pyridine, α-, β-, and γ-picoline coordinated to the paramagnetic heteropolyanion [Ni3(PW9O34)2]12- (P2Ni3) are reported. NMR lines are assigned to [Ni3(ptl)n(PW9O34)2]12- (n=1, 2 or 3; ptl=pyridine-type ligand) on the basis of their [P2Ni3]/[ptl] dependence. The formation constants for γ-picoline complexes at 25 ℃ are K1=80, K2=610, and K3=190 L mol-1. The monopicoline complex has greater affinity for γ-picoline than P2Ni3. A degradation product, [Ni2(WO2)(PW9O34)2]12-, was also identified at low pH by measuring the NMR spectrum of pyridine coordinated to it. The isotropic NMR shifts come mainly from the contact interaction due to σ-electron delocalization.

• 공업화학
• /
• 제9권7호
• /
• pp.1018-1022
• /
• 1998

본 연구에서는 테트라하이드로퓨란(THF)의 개환중합반응에 의해 변형된 12-몰리브도인산의 특성 및 촉매 반응성을 살펴보았다. 기상 에탄올 전화반응에서 THF에 의해 변형된 12-몰리브도인산은 모산 촉매보다 매우 우수한 전환율 및 생성물 수율을 보였다. 변형된 12-몰리브도인산의 증가된 반응성은 변형된 헤테로폴리음이온의 구조적 유연성과 약화된 수소결합에 기인하는 것으로 판단된다. THF는 양성자 또는 결정수를 매개로 헤테로폴리산과 상호작용을 하는 것으로 나타났는데, 결정수를 중심으로 한 THF와 헤테로폴리음이온간의 상호작용이 변형된 12-몰리브도인산의 촉매 활성을 결정하는 주된 요인이었다.

• Bulletin of the Korean Chemical Society
• /
• 제15권9호
• /
• pp.752-758
• /
• 1994

Several one-electron reduction products of ${\gamma}$(1,2)-[$H_nSiV_2W_{10}O_{40}]^{(6-n)-}$ were separated by precipitating or coprecipitating with diamagnetic host compounds at different pH. Mono-and diprotonated species, 1 and 2, in powder samples exhibit aPR spectra characteristic of a mononuclear oxovanadium species, indicating that the unpaired electron is trapped at one vanadium atom. The EPR spectrum of the unprotonated species 0 shows 15 parallel lines, indicating that the unpaired electron interacts equally with two vanadium atoms. While different species were precipitated depending upon the pH of the solution and the charge of the host anion, only one species 1' was formed in the frozen solutions at pH 3.2-4.7. The EPR spectrum of 1' indicates that the unpaired electron is trapped at one vanadium atom and 1/16 of the spin density is delocalized onto the second vanadium atom. The species 1' is probably another form of the monoprotonated species. The EPR spectra show that some of 2 transform into 1 and some of 0 transform into 1' in the solid state at low temperatures. It is suggested that proton transfer between the heteropolyanion and water molecues in the solid state is involved in these transformations.

• Bulletin of the Korean Chemical Society
• /
• 제15권8호
• /
• pp.673-679
• /
• 1994

$^1H$ NMR spectra of imidazole, 2-and 4(5)-methylimidazole, histamine, L-histidine, L-histidine methyl ester, N${\alpha}$-acetyl-L-histidine, and L-carnosine coordinated to the paramagnetic undecatungstocobalto(II)silicate ($SiW_{11}Co$) and undecatungstonickelo(II)silicate ($SiW_{11}Ni$) anions are reported. For these complexes the ligand exchange is slow on the NMR time scale and the pure resonance lines of the free ligand and the complexes have been observed separately at room temperature. Two different complexes are formed, depending upon which nitrogen atom of the imidazole ring is coordinated to the cobalt or nickel ion of $SiW_{11}M$. Thus the NMR spectrum of a $D_2O$ solution containing a ligand and $SiW_{11}M$ consists of three sets of lines originating from the free ligand and two complexes. All NMR lines of the $SiW_{11}Co$ complexes have been assigned unequivocally using the saturation transfer technique. The temperature dependence of some spectra are also reported. The NMR spectra of some complexes show that the internal rotation of the substituent on the imidazole ring is hampered by the heteropolyanion moiety even at room temperature.