Motional freedom of dimethylammonium ions in a cyanoelpasolite, [(CH3)2NH2]2KCo(CN)6, which exhibits phase transition associated with a distinct change in dielectric property.

The temperature dependence of the 1H nuclear magnetic resonance spin-lattice relaxation time T1 of [(CH3)2NH2]2KCo(CN)6 and the partially deuterated analogue [(CD3)2NH2]2KCo(CN)6 has been reported. A change in the molecular motion of organic cations through the first-order phase transition at Tc = 246 K has been discussed. Although this first-order transition has been reported as an isosymmetric transition, in which the space group of the crystal does not change, the number of the 14N nuclear quadrupole resonance line changed from three in the high-temperature phase to twelve in the low-temperature phase indicating the lowering of crystal symmetry.

ESR study of molecular orientation and dynamics of TEMPO derivatives in CLPOT 1D nanochannels.

The molecular orientations and dynamics of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical derivatives with large substituent groups at the 4-position (4-X-TEMPO) in the organic one-dimensional nanochannels within the nanosized molecular template 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) were examined using ESR. The concentrations of guest radicals, including 4-methoxy-TEMPO (MeO-TEMPO) or 4-oxo-TEMPO (TEMPONE), in the CLPOT nanochannels in each inclusion compound (IC) were reduced by co-including 4-substituted-2,2,6,6-tetramethylpiperidine (4-R-TEMP) compounds at a ratio of 1 : 30-1 : 600. At higher temperatures, the guest radicals in each IC underwent anisotropic rotational diffusion in the CLPOT nanochannels. The rotational diffusion activation energy, Ea , associated with MeO-TEMPO or TEMPONE in the CLPOT nanochannels (6-7 kJ mol(-1) ), was independent of the size and type of substituent group and was similar to the Ea values obtained for TEMPO and 4- hydroxy-TEMPO (TEMPOL) in our previous study. However, in the case in which TEMP was used as a guest compound for dilution (spacer), the tilt of the rotational axis to the principal axis system of the g-tensor, and the rotational diffusion correlation time, τR , of each guest radical in the CLPOT nanochannels were different from the case with other 4-R-TEMP. These results indicate the possibility of controlling molecular orientation and dynamics of guest radicals in CLPOT ICs through the appropriate choice of spacer. Copyright © 2016 John Wiley & Sons, Ltd.

ESR study of molecular orientation and dynamics of nitronyl nitroxide radicals in CLPOT 1D nanochannels.

New inclusion compounds (ICs) were prepared using the organic 1D nanochannels of 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) as a nanosized template and nitronyl nitroxide (NN) radicals such as phenylnitronylnitroxide (PhNN) and p-nitrophenylnitronylnitroxide (p-NPNN). ESR measurements below 255 K for the CLPOT ICs diluted with spacer molecules gave rigid limit spectra similar to that for PhNN molecules in a glassy ethanol matrix at low temperature, which suggests isolation of the radical molecules. ESR measurements for them in the range of 290-400 K gave a modulated quintet ESR signal, which suggested uniaxial rotational diffusion of NN radicals in the nanochannels approximately around the principal y-axis of the g-tensors. In the ESR measurements to 430 K for the [(CLPOT)2-(p-NPNN)0.07] IC without spacers, the broader line width than the case in dilution was observed by inter-radical dipolar interaction. In every case, the rotational diffusion activation energies of NN radicals in the CLPOT nanochannels were several times larger than those of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical derivatives (4-X-TEMPO) in CLPOT nanochannels. This is expected due to the larger molecular size of NN radicals than 4-X-TEMPO or stronger interaction between NN radicals and the surrounding host or guest molecules.

Molecular orientation and dynamics of different sized organic radicals included in organic 1D nanochannels.

The molecular orientation and dynamics of di-t-butylnitroxide (DTBN) and 4-oxo-2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPONE) radicals in the organic 1D nanochannels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) were investigated by examining inclusion compounds (ICs) diluted by the co-inclusion of nonradicals using electron spin resonance (ESR). Spectral simulation showed that the axial rotation of DTBN or TEMPONE molecules is excited in TPP nanochannels with activation energies of 3 and 10 kJ mol(-1), respectively. The rotation axes for both DTBN and TEMPONE were determined to be almost parallel to the principal y-axis of the g tensor, which agrees with the result reported for 2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPO) in TPP nanochannels, which has the activation energy of 5 kJ mol(-1). These results indicate that the molecular orientations of guest nitroxide radicals are almost independent of the molecular sizes of the guest radicals in TPP nanochannels, although the molecular dynamics are dependent on the molecular sizes.

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.

Temperature dependence of one-dimensional hydrogen bonding in morpholinium hydrogen chloranilate studied by 35Cl nuclear quadrupole resonance and multi-temperature X-ray diffraction.

The temperature dependence of (35)Cl NQR frequencies and the spin-lattice relaxation times T(1) has been measured in the wide temperature range of 4.2-420 K for morpholinium hydrogen chloranilate in which a one-dimensional O-HO hydrogen-bonded molecular chain of hydrogen chloranilate ions is formed. An anomalous temperature dependence of the NQR frequencies was analyzed to deduce a drastic temperature variation of the electronic state of the hydrogen-bonded molecular chain. The hydrogen atom distribution in the OHO hydrogen bond is discussed from the results of NQR as well as multi-temperature X-ray diffraction. Above ca. 330 K, the T(1) showed a steep decrease with an activation energy of ca. 70 kJ mol(-1) and with an isotope ratio (37)Cl T(1)/(35)Cl T(1) = 0.97 ± 0.2. The orientational change of the z axis of electric field gradient tensor in conjunction with the hydrogen transfer between adjacent hydrogen chloranilate ions is suggested as a possible relaxation mechanism.

ESR study of the molecular orientation and dynamics of stable organic radicals included in the 1-D organic nanochannels of 2,4,6-tris-4-(chlorophenoxy)-1,3,5-triazine.

The molecular orientation and dynamics of the organic stable radicals such as 2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPO) or 4-hydroxy-TEMPO (TEMPOL) included in the one-dimensional (1-D) organic nanochannels of 2,4,6-tris-4-(chlorophenoxy)-1,3,5-triazine (CLPOT) were investigated by examining the inclusion compounds (ICs) diluted by the co-inclusion of non-radicals using ESR spectroscopy. Spectral simulation showed that the axial rotation of TEMPO or TEMPOL molecules is excited in the nanochannels with activation energies of 8 and 7 kJ mol(-1) , respectively. The rotation axis was estimated to be tilted towards the principal x direction in the axis system of the g-tensor of the respective radicals. This is quite different from that for similar ICs in the nanochannels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP), in which the radicals are axially rotating around the principal axis y of the g-tensor. The difference is attributed to the larger nanospace of the CLPOT nanochannels.

A 14N nuclear quadrupole resonance study of phase transitions and molecular dynamics in hydrogen bonded organic antiferroelectrics 55DMBP-H2ca and 1,5-NPD-H2ca.

The temperature dependence of the (14)N NQR frequencies has been measured in antiferroelectric and paraelectric 55DMBP-H(2)ca and 1,5-NPD-H(2)ca. In both compounds we observe two non-equivalent nitrogen positions (N(+)-H···O(-) and N···H-O) in the antiferroelectric phase. The two nitrogen positions become equivalent (N···H···O) in the paraelectric phase. The critical exponent of the local antiferroelectric order parameter has been determined from the NQR data. The principal values of the quadrupole coupling tensor correlate in both compounds. The correlation diagrams clearly show how a proton migrates from the antiferroelectric position towards the paraelectric position in the bifurcated hydrogen bond on increasing the temperature. A slow motion has been observed in 55DMBP-H(2)ca by the (1)H and (14)N spin-lattice relaxation. An analysis of the spin-lattice relaxation data suggests a slow exchange between two non-planar conformations of the bipyridine molecule.

Correlation between proton transfer and (35)Cl NQR frequency as well as molecular geometry of chloranilic acid in co-crystals with some organic bases.

Proton transfer in hydrogen-bonded organic co-crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The (35)Cl NQR frequencies of chloranilic acid molecule as well as (14)N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double-resonance methods, respectively. The extent of proton transfer in the O...H...N hydrogen bond was estimated from Townes-Dailey analysis of the (14)N NQR parameters. The (35)Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the pi-electron system of chloranilic acid. Geometry dependence of the O...H...N hydrogen bond, i.e. the H-N valence bond order versus the hydrogen-bond geometry correlation is also discussed.

14N NQR and proton NMR study of ferroelectric phase transition and proton exchange in organic ferroelectric (H2-TPPZ)(Hca)2.

The complete (14)N nuclear quadrupole resonance spectrum has been measured in ferroelectric (H(2)-TPPZ)(Hca)(2) using nuclear quadrupole double resonance. The quadrupole coupling tensors are assigned to various nitrogen positions in the crystal structure. Two types of asymmetric N-H(+)...N hydrogen bonds are observed in the ferroelectric phase. A slow dynamics influencing the (14)N NQR spectrum and relaxation has been observed in the paraelectric phase. The analysis of the (14)N NQR spectra in the paraelectric phase shows that above T(c) each hydrogen bond exchanges between the two types observed in the ferroelectric phase. The change of the type of hydrogen bond is associated with the transfer of protons within the bond.

Two solid phases of pyrimidin-1-ium hydrogen chloranilate monohydrate determined at 225 and 120 K.

The crystal structures of two solid phases of the title compound, C(4)H(5)N(2)(+) x C(6)HCl(2)O(4)(-) x H(2)O, have been determined at 225 and 120 K. In the high-temperature phase, stable above 198 K, the transition temperature of which has been determined by (35)Cl nuclear quadrupole resonance and differential thermal analysis measurements, the three components are held together by O-H...O, N...H...O, C-H...O and C-H...Cl hydrogen bonds, forming a centrosymmetric 2+2+2 aggregate. In the N...H...O hydrogen bond formed between the pyrimidin-1-ium cation and the water molecule, the H atom is disordered over two positions, resulting in two states, viz. pyrimidin-1-ium-water and pyrimidine-oxonium. In the low-temperature phase, the title compound crystallizes in the same monoclinic space group and has a similar molecular packing, but the 2+2+2 aggregate loses the centrosymmetry, resulting in a doubling of the unit cell and two crystallographically independent molecules for each component in the asymmetric unit. The H atom in one N...H...O hydrogen bond between the pyrimidin-1-ium cation and the water molecule is disordered, while the H atom in the other hydrogen bond is found to be ordered at the N-atom site with a long N-H distance [1.10 (3) A].

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.

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.

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.