• Bulletin of the Korean Chemical Society
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• v.20 no.10
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• pp.1149-1152
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• 1999

1H NMR spectrum of a DMF-d7 solution containing 4-aminopyrimidine and [SiW11CoIIO39]6- (SiW11Co) shows separate peaks from two linkage isomers, a and b, in which N(1) and N(3) of the pyrimidine ring are coordinated to SiW11Co, respectively. The signal from the amine group in the isomer a exhibits temperature dependence that is characteristic of a two-site exchange problem. Rates of internal rotation of the amine group were determined by simulating the NMR spectra at 5-35℃. The amine group of free 4-aminopyrimidine also shows temperature-dependent spectra at lower temperatures; rates of internal rotation at (-25)-25℃ were determined. The internal rotation of the amine group in the complex is much slower than that for free 4-aminopyrimidine, indicating that π-character of the C-N bond increases on coordination to SiW11Co. The amine group in the isomer b does not show such behavior. It is probable that hydrogen bonding between N-H and a bridging oxygen atom of SiW11Co prevents it from rotating at low temperatures.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.107-110
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• 2000

($^{11}$B NMR measurements have been performed on single crystals of LuNi$_2$B$_2$C superconductor to investigate vortex lattice structures and dynamical behavior. The spectrum in the superconducting state is significantly broadened by local field inhomogeneity due to the vortex lattice and the peak point of the spectrum shifts toward low magnetic field due to the imperfect field penetration. The linewidth of the spectrum reflecting local field variation is much smaller than expected for conventional vortex lattices and shows peculiar increase at low temperature. Furthermore, the transverse relaxation rate, 1/T$_2$, probing the slow motion of vortices, exhibits a single peak as temperature decreases. These prominent results highlight significant fluctuation of vortices even for this low T$_c$, and nearly isotropic 3D superconductor.

• Bulletin of the Korean Chemical Society
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• v.4 no.3
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• pp.103-114
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• 1983

The NMR shift arising from the electron angular momentum and the electron spin dipolar-nuclear spin angular momentum interaction has been examined for a $3d_1$ system in a strong octahedral crystal field when the threefold axis is chosen as the quantization axis. To investigate the NMR shift in this situation, first, we have extended the evaluation of the hyperfine integrals to any pairs of 3d orbitals adopting a general method which is applicable to a general vector R, pointing in arbitrary direction in space. Secondly, a general expression using a nonmultipole technique is derived for the NMR shift resulting from the electron angular momentum and the electron spin dipolar-nuclear spin angular momentum interactions. From this expression all the multipolar terms are determined. ${\Delta}B/B$ for the $3d_1$ system in this case is compared with that for the 3d1 system when the z axis is chosen as the quantization axis. When we choose the threefold axis as the quantization axis, it is found that along the , and axes, ${\Delta}B/B$ values are significantly different from each other and along the , <-1-1-1>, <-11-1>, , <-1-11>, , and <-111> axes, ${\Delta}B/B$ values are however the same. We also find that the 1/R7 term contributes dominantly to the NMR shift for all values of R. When 1/$R^5$ term is included, there is good agreement between the exact solution and the multipolar terms when $R\; {\leqslant}\;0.35\;nm.$.

• Korean Journal of Crystallography
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• v.12 no.3
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• pp.141-144
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• 2001

From the reaction of Na[Ga(N₃)₄] with PPh₃, an ionic compound [Ph₃P(OH)]/sup +/[N₃]/sup -/ (1) was isolated. Compound 1 was characterized by spectroscopy (¹H-NMR, /sup 13C{¹H}-NMR, and IR) and X-ray diffraction. Crystallographic data for 1 : orthorhombic space group P2₁2₁2₁, a = 10.491 (4) Å, b=11.603(5)Å, c=13.149(5)Å, Z=4, R(wR₂)=0.0547(0.0978).

• Superconductivity and Cryogenics
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• v.11 no.2
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• pp.23-29
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• 2009

The unique features of HTS offer opportunities and challenges to a number of applications. In this paper we focus on NMR and MRI magnets, illustrating them with the NMR/MRI magnets that we are currently and will shortly be engaged: a 1.3 GHz NMR magnet, an "annulus" magnet, and an $MgB_2$whole-body MRI magnet. The opportunities with HTS include: 1) high fields (e.g., 1.3 GHz magnet); 2) compactness (annulus magnet); and 3) enhanced stability despite liquid-helium-free operation ($MgB_2$whole-body MRI magnet). The challenges include: 1) a large screening current field detrimental to spatial field homogeneity (e.g., 1.3 GHz magnet); 2) uniformity of critical current density (annulus magnet); and 3) superconducting joints ($MgB_2$magnet).

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.961-965
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• 1997

1H NMR spectra of 3,3-dimethylpiperidine (1) at -70 to 30 ℃ exhibit gradual change from slow to rapid exchange between two alternate chair forms. The exchange rate constant was determined as a function of temperature by simulating the line shape of the signal from the two methyl groups using the modified Bloch equations. The resulting free energy of activation is ΔG* = 44.4±1.9 kJ mol-1 at 298 K. The 1H NMR spectrum of a D2O or dimethylsulfoxide-d6 (DMSO-d6) solution containing 1 and [SiW11CoⅡO39]6- exhibits separate signals for the free ligand and the complex, indicating that the ligand exchange is slow on the NMR time scale. In D2O the piperidine ring is frozen as a chair form even at room temperature with the cobalt ion bonded to the axial position of the nitrogen atom. When DMSO-d6 is added to the D2O solution, the NMR spectral change suggests that a rapid exchange occurs between the chair form and another conformer. It is proposed that the conformation of ^b1^b coordinated to [SiW11CoⅡO39]6- in DMSO-d6 is close to a twist form.

• Journal of the Korean Magnetic Resonance Society
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• v.9 no.1
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• pp.61-66
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• 2005

$^{11}B MAS NMR$ spectra of binary glass system $xV_2O5-B_2O_3$ and ternary glass system $xV_2O5-B_2O_3-yNa_2O$ (x = $V_2O_5 mol%/$B_2O_3$ mol%, y = $Na_2O$ mol$/$B_2O_3$ mol%) were acquired. $BO_3$ units are dominant components in the spectra of $xV_2O_5-B_2O_3$glass systems while both $BO_3$ and $BO_4$ unit appear in comparable amounts in the spectra of $xV_2O_5-B_2O_3-yNa_2O$ glass systems. More $BO_3$ units were monitored for higher $V_2O_5$ contents while more $BO_4$ unit for higher $Na_2O$ contents. Quadrupole parameters such as $e^2qQ$ and $\eta$ obtained form spectral simulation indicate that $e^2qQ$ has a maximum value at x = y 1 and $\eta$ decreases and increases as x or y grows, respectively. Our results suggest that $V_2O_5$ and $Na_2O$ play opposite roles in the ternary glasses.

• Bulletin of the Korean Chemical Society
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• v.19 no.11
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• pp.1244-1248
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• 1998

Ozonolysis reactions of cyclic olefins 1a-c and norbomene In in the presence of trifluoroactophenone 6 provided the corresponding cross-ozonides 7a-c and 7n. Further reactions of ozonides 7a-c and 7n with the independently prepared carbonyl oxide 11 gave diozonides of structure l0a-c and 10n. The ozonolysis of 1methylcyclopentene 12a and 1-methylcyclohexene 12b in the presence of trifluoroactophenone 6 provided exclusively ozonide 15 and 16 derived from capture of carbonyl oxide 13. All of the new ozonides have been isolated as pure substances and characterized by their 1H NMR and 13C NMR spectra.

• Journal of the Korean Magnetic Resonance Society
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• v.3 no.2
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• pp.90-99
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• 1999

Doping of boron atoms in graphite has been well known method to increase the discharge capacity as the negative electrode material for lithium secondary battery. Herein, the boron-doped graphites are prepared by mixing 1, 2.5, 5, and 7 wt. % of boron carbide in carbon during the graphitizing process. The structural states of boron in boron-doped graphites are investigated by solid-state 11B NMR spectroscopy. The resonance lines for substitutional boron atoms are identified as the second order quadrupolar powder pattern with the quardrupole coupling constant, QCC = 3.36(2) MHz. The quantitative analysis of 11B NMR spectra with boron-doped graphite has also been performed via simulation.

• Korean Journal of Materials Research
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• v.15 no.12
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• pp.786-790
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• 2005

We investigated the particularity of temperature and composition changes in $xNa_2O{\cdot}(52.5-x)B_2O_3{\cdot}47.5SiO_2$ glasses by use of FT-IR, $^{11}B$ NMR, Raman spectrometer. From FT-IR and $^{11}B$ NMR spectrometer, we thought that tetrahedral boron, $BO_4$ units are created $N_4$ increasing tendency generated near $600^{\circ}C$. It's expected that composition ana heat treatment directly contributed to structural changes, this changes are following to $Na_2O$ increasing or decreasing. caused by $N_4\;and\;BO_4$ units are caused by relatively increasing or decreasing in the glasses' structure. Particularly, $BO_4$ units are converted to $BO_3$ units after $600^{\circ}C$ heat treatment for 50h in the composition of $x<18(R<0.5,\;R=Na_2O/B_2O_3\;mol\%)$. On the order hand, $BO_3$ units are converted to, $BO_4$ units after $600^{\circ}C$ heat treatment for 50h in the composition of $x{\geq}18\;(R>0.5)$. This particularity of composition and temperature dependence of structural changes are similarly represented by Raman analysis results.