Tetsuo Asaji

Hydrogen bonding in 1,2-diazine–chloranilic acid (2 : 1) studied by a 14N nuclear quadrupole coupling tensor and multi-temperature X-ray diffraction

Protons involved in the H-bond system in 1,2-diazine-chloranilic acid (2 : 1) are assumed to be in jumping motion in the double-minimum potential corresponding to the two extreme electronic states of O-H...N and O-...H-N+. 14N nuclear quadrupole coupling constants were determined by 1H-14N nuclear quadrupole double resonance. Assuming that the observed coupling constants are result of a fast exchange of the two extreme electronic states, the coupling constants for each state were estimated by use of the equilibrium populations of the two extreme states determined from multi-temperature X-ray single-crystal diffraction. It was suggested that not only the population but also the electron distribution of the extreme electronic states itself changes with temperature.

Phase transition and temperature dependent electronic state of an organic ferroelectric, phenazine–chloranilic acid (1:1)

The isotope effect of hydrogen motion in an organic ferroelectric, phenazine (Phz)–chloranilic acid (H2ca and D2ca for normal and deuterated compounds, respectively) co-crystal, was studied by 35Cl nuclear quadrupole resonance (NQR). Besides a ferroelectric transition at Tc = 253 K (303 K), a neutral-to-ionic transition was found below 170 K (200 K) for Phz–H2ca (Phz–D2ca). 1H–14N nuclear quadrupole double resonance measurements were also made in order to study the temperature dependent electronic state of Phz–(H/D)2ca. 14N NQR parameters suggested that donor orbital populations of the two nitrogen atoms in a phenazine molecule become nonequivalent (1.78 and 1.97) in the ferroelectric phase, while they are both equal to 1.89 in the paraelectric phase. In the ionic phase of Phz–D2ca, which was obtained by cooling below 188 K, they became 1.50 and 1.95, suggesting a proton transfer from D2ca to Phz.

Hydrogen bonding in two solid phases of phenazine-chloranilic acid (1/1) determined at 170 and 93 K.

The crystal structures in two solid phases, i.e. phase II stable between 146 and 253 K and phase IV below 136 K, of the title compound [phenazine-chloranilic acid (1/1), C12H8N2.C6H2Cl2O4, in phase II, and phenazinium hydrogen chloranilate, C12H9N2+.C6HCl2O4-, in phase IV], have been determined. Both phases crystallize in P2(1), and each structure was refined as an inversion twin. In phase II, the phenazine and chloranilic acid molecules are arranged alternately through two kinds of O-H...N hydrogen bonds. In phase IV, salt formation occurs by donation of one H atom from the chloranilic acid molecule to the phenazine molecule; the resulting monocation and monoanion are linked by N-H...O and O-H...N hydrogen bonds.

Phase Transition and Ring-Puckering Motion in a Metal–Organic Perovskite [(CH2)3NH2][Zn(HCOO)3]

Phase transitions in a metal-organic perovskite with an azetidinium cation, which exhibits giant polarizability, were investigated using differential scanning calorimetry (DSC) and (1)H nuclear magnetic resonance (NMR) measurements. The DSC results indicated successive phase transitions at 254 and 299 K. The temperature dependence of the spin-lattice relaxation time T(1) determined by NMR indicated that the activation energy for cation ring-puckering motion was 25 kJ mol(-1) in phase I (T > 299 K). The potential energy at the transition state of puckering is expected to decrease when the potential for the motion becomes asymmetric with decreasing temperature in phases II and III. A possible mechanism for the onset of an extraordinarily large dielectric anomaly is discussed.

One-dimensional spin dynamics in a halogen-bridged mixed-valence palladium (II), (IV) complex studied by 1H NMR

Abstract The 1 H NMR spin—lattice relaxation time T 1 of [Pd(chxn) 2 ][PdBr 2 (chxn) 2 ]Br 4 (chxn = 1R,2R-cyclohexanediamine) in the solid state was measured between 90 K and room temperature at Larmor frequencies of 10–60 MHz. The presence of thermally activated diffusive spins formed on paramagnetic Pd III sites along the halogen-bridged 1D chain was revealed from the Larmor frequency dependence of T 1 . The diffusion rates were estimated to be 2 × 10 13 , 9 × 10 11 , and 6 × 10 10 rad s −1 at 303, 198 and 125 K, respectively. The rate observed around room temperature showed an Arrhenius-type temperature dependence with an activation energy of ≈1700 K. It is shown that the diffusive spin is delocalized over several Pd sites. The observed spin motion is attributable to the neutral soliton by referring to the electrical conductivity data.

Intrinsic paramagnetism of doped polypyrroles and polythiophenes: Electron spin resonance of the polymers prepared by the use of copper(II) compounds as oxidative coupling agents

Abstract Electron spin resonance studies were carried out on the perchlorate and trifluoromethanesulfonate (triflate) of polypyrrole and polythiophene, which were prepared by polymerizing an appropriate monomer by the use of copper(II) perchlorate or triflate as an oxidative coupling agent. The linewidth was largely influenced by the nature of the counter anions as well as by the adsorbed oxygen. The signal intensity observed for all the materials including both the oxygen-free and the oxygen-adsorbing polymers was very weakly temperature dependent, in contrast to the Curie-type paramagnetism already reported for electrochemically prepared polypyrrole: the Weiss constant was 225 – 573 K depending on the nature of the polymers. This suggests the presence of a strong antiferromagnetic interaction between unpaired electrons involved in the polymer chains; polarons as well as defect spins are possible paramagnetic species.

Hydrogen bonding in 1,2‐diazine–chloranilic acid (2/1) and 1,4‐diazine–chloranilic acid (2/1) determined at 110 K

The crystal structures of the isomeric title compounds [systematic names: pyridazine-2,5-dichloro-3,6-dihydroxy-p-benzoquinone (2/1), (I), and pyrazine-2,5-dichloro-3,6-dihydroxy-p-benzoquinone (2/1), (II)], 2C(4)H(4)N(2) x C(6)H(2)Cl(2)O(4), have been redetermined at 110 K. The H atom in the intermolecular O...H...N hydrogen bond in each compound was revealed to be disordered; the relative occupancies at the O and N sites are 0.33 (3) and 0.67 (3), respectively, for (I), and 0.56 (4) and 0.44 (4) for (II). The formal charges of the chloranilic acid in (I) and (II) estimated from the occupancy factors are ca -1.3 and -0.8, respectively. The geometries of the centrosymmetric chloranilic acid molecule in (I) and (II) are compared with the neutral, monoanionic and dianionic forms of chloranilic acid optimized by density functional theory (DFT) at the B3LYP/6-311+G(3df,2p) level. The result implies that the chloranilic acid molecule in (I) is close to the monoanionic state, while that in (II) is between neutral and monoanionic, consistent with the result derived from the H-atom occupancies.

Preparation and Characterization of New Inclusion Compounds Using Stable Nitroxide Radicals and an Organic 1-D Nanochannel as a Template

A new inclusion compound (IC) using di-t-buthyl nitroxide (DBNO) radical and tris(o-phenylenedioxy)cyclotriphosphazene (TPP) (1), which has an organic one-dimensional (1-D) nanochannel in the crystal, is reported. According to the characterization using thermogravimetric analysis (TG), ESR measurements, etc., the composition of the inclusion compound was assigned as TPP:DBNO = 1:0.62. The narrowing of the isotropic ESR adsorption line of 1 was observed with a temperature increase from 103 K to room temperature. The line shape indicated a type of 1-D spin diffusion as observed in our previous study of the IC using TPP and 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO).

On the crystal structures of some protonic complexes of oxo-ligands with tetrachloroauric acid, [(RO)nH][AuCl4] (R: Py, Ph3As; n: 1, 2), prepared from deuterated and non-deuterated solvent systems

Abstract The possible structural change of the dimeric cations [(RO)nH]+ (R=Py, Ph3As) in [(RO)nH][AuCl4] crystals due to the lowering of temperature or hydrogen–deuterium exchange was studied by 35Cl NQR and powder X-ray diffraction measurements. Temperature dependence of the nuclear quadrupole resonance (NQR) frequencies of [(Ph3AsO)2H][AuCl4] and [(PyO)2H][AuCl4] suggested the symmetric hydrogen bond was retained down to 4.2 K. A crystalline polymorph of [(PyO)2H][AuCl4] (partial deuterate) was found to be stabilized preferably by the deuteration. The crystal structure determination of the partial deuterate by single crystal X-ray diffraction method revealed that the two pyridine N-oxide (PyO) moieties in the dimeric cation [(PyO)2H/D] are non-equivalent and the crystal structure is completely different from that of the non-deuterated salt.

EPR study of polyaniline perchlorates: Spin species related to charge transport

Abstract The spin susceptibilities χ of polyaniline perchlorates prepared by different methods were determined from electron paramagnetic resonance spectra. The observed χ vs. T curves can be explained by the sum of a Curie term and a thermally activated term. The C-spin species which is responsible for the Curie term is produced upon protonation of polyaniline base, but the concentration is independent of the protonation level. In contrast, the concentration of the TA-spin species that shows the thermally activated susceptibility has a close correlation with macroscopic electrical conductivity. Both spin species are intrinsic of polyaniline salts, and the TA-spin species is expected to be responsible for interchain hopping of charge carriers.