The title compound, C₂₀H₂₂BNO₂, has a polarized π-system due to resonance between N—C(H)=C(H)—B and ionic N⁺=C(H)—C(H)=B⁻ canonical structures. The dihedral angles between the ethenyl plane (r.m.s. deviation for C₂H₂ = 0.0333 Å) with the ethenyl-<italic>C</italic>(NC₂-pyrrole) plane (r.m.s. deviation CNC₂ 0.0423 Å) and the ethenyl-C(BO₂-1,3,2-dioxaborolane) plane (r.m.s. deviation BCO₂ 0.0082 Å) are 45.86 (8) and 37.47 (8)°, respectively, and are greater than those found for the previously reported <italic>E</italic>-isomer [Hatayama &amp; Okuno (2012) <italic>Acta Cryst.</italic> E<bold>68</bold>, o84]. In comparison with the <italic>E</italic>-isomer, the reduced planarity of <italic>Z</italic>-isomer results in a decrease of the contribution of the N⁺=C(H)—C(H)=B⁻ canonical structure.

The title compound, C₂₄H₁₈N₂O, was been described previously in the space group <italic>P</italic>2₁/<italic>c</italic> with <italic>Z</italic> = 4 [Kawashima &amp; Okuno (2017). <italic>IUCrData</italic>, <bold>2</bold>, x170277]. The current <italic>P</italic>\overline{1} polymorph was obtained from a chloroform–ethanol solution. The molecular structure in this polymorph is slightly different from the previously reported structure, with different dihedral angles of the two <italic>N</italic>-phenyl groups to the ynamine plane; these are 79.99 (11) and 12.09 (11)° in the polymorph reported here. The molecules form dimers through four C—H...π interactions. Furthermore, in this polymorph, the molecules stack along the <italic>a</italic> axis to form a molecular arrangement that would be suitable to promote the solid-state polymerization of diacetylenes.

In the title pentanedinitrile derivative, C₁₁H₉IN₂, the iodophenyl group is connected at the 3-position. The central propylene chain of the pentanedinitrile moiety contains one <italic>gauche</italic> conformation as a result of steric repulsion with the phenyl ring. Intermolecular close contacts in the crystal comprise a weak C<italic>sp</italic>
³—H...N hydrogen bond and a C—I...N halogen bond.

The title compound, C₁₉H₁₄N₂O₄, was found to have two crystal polymorphs, in which the molecular structures of the diacetylenic compound are broadly similar. The main structural difference between the polymorphs concerns the intermolecular hydrogen-bonding motifs adopted, namely a one-dimensional zigzag polymer linked by N—H...N(py) (py is pyridine) interactions in polymorph I and a centrosymmetric dimeric motif formed by N—H...O=C interactions in polymorph II. The diacetylene cores of the molecules stack along the <italic>a</italic> and <italic>b</italic> axes in polymorphs I and II, respectively. It was found that only the molecular arrangement in polymorph II satisfies Baughman's criterion to afford polydiacetylenes (PDAs) by thermal annealing or irradiation with light. This predicted polymerization activity was confirmed by experiment.

In the title diacetylene derivative, C₁₆H₁₂N₂O, the amino plane makes dihedral angles of 3.90 (4) and 60.53 (4)°, respectively, with the pyridyl and phenyl rings, indicating that an electron-deficient pyridyl ring makes better conjugation with a lone pair of the amino nitrogen atom. In the crystal, molecules form inversion dimers<italic>via</italic>pairs of hydrogen bonds between the hydroxy and pyridyl groups, with an O...N distance of 2.7765 (16) Å. The dimers stack along the<italic>a</italic>axis, but the title compound shows little solid-state polymerization reactivity.

The title compound, C₁₉H₁₇Cl₂NSSi, is an enamine derivative, in which the N atom adopts a shallow trigonal–pyramidal geometry [displacement from the plane of its attached C atoms = 0.1383 (18) Å]. The dihedral angle between the plane through the three amino carbon atoms and the vinyl group is 89.47 (7)°. The phenothiazine unit has a butterfly structure and the central six-membered ring adopts a boat conformation. The fold angle between the benzene rings is 28.52 (7)°. The crystal structure features weak C<italic>sp</italic>³—H...Cl hydrogen bonds, H...S contacts and π–π stacking interactions between phenothiazine units.

In the title compound, C₂₉H₂₃N₃, the molecule has an unsymmetrical structure, although it can possess<italic>Cs</italic>symmetry. The NC_{<italic>3</italic>}units around the amino N atoms are approximately planar and make dihedral angles of 13.41 (5) and 31.05 (5)° with the pyridine ring. In the crystal, C—H...N interactions between the phenyl and pyridyl rings lead to a columnar stack along the<italic>b</italic>axis.

In the title compound, C₂₄H₁₈N₂O₁, the ynamine moiety has a near-planar structure (r.m.s. deviation = 0.0200 Å), and makes dihedral angles of 52.99 (7) and 27.91 (7)° with the phenyl rings. In the crystal, the molecules exhibit a dimeric form owing to bifurcated C—H...π interactions within a centrosymmetric dimer. Intermolecular N—H...O hydrogen bonds are also formed along the<italic>b-</italic>axis direction.

A novel diacetylene derivative, N,N'-bis[5-(3-tolylaminocarbonyloxy)-1,3-pentadiynyl]-N,N'-diphenyl-1,4- phenylenediamine (1), was prepared, where two diacetylene groups were connected by a 1,4-phenylenediamine moiety. The molecules stacked one-dimensionally and showed solid-state-polymerization reactivity above 80 degrees C. The decay of the monomers at 100 degrees C proceeded gradually without a marked induction period and was fully completed after 400 h. The obtained polymer was a crystalline solid judged by powder X-ray diffraction (PXRD) patterns and SEM imaging. The conjugated pi-system of the obtained polymer was classified as a two-legged conjugated ladder. The polymer showed a broad absorption from the visible to the near IR region, indicating a decrease in the optical band gap of ca. 1.0 eV, because of the expansion of the pi-conjugated system from a one-dimensional system to a ladder. The ladder polymer showed high conductivity after I(2) doping from sigma(293K) = 5 x 10(-12) S cm(-1) to 1.2 x 10(-5) S cm(-1). The conductivity depended heavily on the pressure of iodine and reached s373K 2.3 x 10(-1) S cm(-1). The activation energy of the ladder polymer was also estimated as 360 meV.

Novel ynamine. compounds, 5-hydroxy-1-(phenothiazine-10-yl)-1,3-pentadiyne (1), its S-oxide (2) and S-dioxide (3), were prepared. Compound 2 was found to show thermal reactivity to give polydiacetylene, however 1 and 3 did not show any reactivity. Compound 2 stacks along the c axis, forming a columnar structure. The condition of molecular arrangement satisfied Baughman's criterion. Significant intermolecular contact between the oxygen atoms of sulfoxide groups and the adjacent sulfur atoms was recognized.

Novel Ni-II(tdaS)(2) complexes, (m - or p-MPYNN)(2)Ni(tdas)(2) (MPYNN = N-methylpyridinium alpha-nitronyl nitroxide and tdas = 1,2,5-thiadiazole-3,4-dithiolate), were prepared. The Ni(tdaS)2 anions are located on the lattice points and at the lattice center in the crystal of (m -MPYNN)(2)Ni(tdas)(2). The m -MPYNN cations form a centrosymmetric dimer, and the anion is sandwiched by a pair of the dimers, forming alternate stacks along the a axis. In the crystal of the (p-MPYNN)2Ni(tdas)(2) complex, the Ni(tdas)(2) anions are located on the lattice points and at the center of the bc plane. The anion is surrounded by four p-MPYNN cations. The p-MPYNN cations also form a centrosymmetric dimer. Each cation has a short contact with a different Ni(tdas)(2) anion. The magnetic susceptibilities of both complexes decrease with decreasing temperature, indicating antiferromagnetic interaction within the radicals. The behavior of (m- and p-MPYNN)(2)Ni(tdas)(2) was understood with the singlet-triplet model and the Curie-Weiss law. (C) 2003 Elsevier Science Ltd. All rights reserved.

The electron spin density distributions of p-N-alkylpyridinium alpha-nitronyl nitroxides with alkyl = methyl (p-MPYNN) and n-butyl (p-BPYNN) were determined in their iodide salts from the temperature dependence of the solid-state high-resolution H-1 MAS NMR spectra. The results were compared with that of p-pyridyl alpha-nitronyl nitroxide (p-PYNN) to see how positive charge on the aromatic ring affects the spin density distribution. This effect was not significant contrary to the effect of incorporation of a nitrogen atom into the aromatic group. The change in the magnitude of the spin density can be ascribed to the dihedral angle between nitroxide and aromatic moieties. Relatively large hyperfine coupling constant of N-methyl proton, which is almost half as large as those of beta-methyl proton, implies the utility of the N-methyl group as an intermolecular magnetic coupler. (C) 2003 Published by Elsevier Science Ltd.

We have measured nuclear spin-lattice relaxation limes T-1 of H-1 in the organic salts mMPYNN(+). ClO4- and m-MPYNN+. BF4- in the temperature range between 2 K and 100 Ii under external fields up to 70 kOe. In these salts, two cationic (spin-1/2) radicals constitute a dimer due to the ferromagnetic interaction J(1). We interpreted the experimental results of T-1(-1) below about 10 K (similar to J(1)/k(B)) in terms of two relaxation processes based on the energy levels of the ferromagnetic dimer. The flip-flop and the direct processes which are due to longitudinal and transverse spin fluctuations become dominant at higher and lower fields, respectively, the crossover field being around 10 kOe. For the field dependence of T-1(-1) at higlrer temperatures, the spin diffusive model of spin-1/2 in a two-dimensional system is satisfactorily applied.

The electron spin density distribution was investigated for p- and m-pyridyl nitronyl nitroxides (p-PYNN and m-PYNN) in the crystalline phase by the temperature dependence of the solid state high resolution H-1-MAS NMR spectrum. The results were compared with that of phenyl nitronyl nitroxide (PNN) for elucidating the effect of incorporation of a nitrogen atom into the aromatic group. For p-PYNN, the magnitude of the negative spin density at 3 and 5 positions of the pyridyl group was suppressed by 30% in comparison with that of PNN and the positive spin density at 2 and 6 positions was slightly enhanced by 10%. On the other hand, the positive spin density at 2, 4 and 6 positions of pyridyl group of m-PYNN was suppressed by 30% in average and the negative one at 5 was also suppressed by 20%. The DFT calculation at UBLYP/6-31G(d, p) level suggested that the molecular geometry largely contributed to the change of the spin density in addition to the effect of incorporation of the nitrogen atom. In fact, the spin density distribution of the aromatic ring of p-PYNN was remarkably reduced in solution compared with that in the crystalline phase.

Zero- and longitudinal-field positive muon spin relaxation (mu(+) SR) measurements were carried out from 300 K to 30 mK to study a ground state of m-MPYNN . BF4 which is known to be a two-dimensional kagome antiferromagnet with S=1 by ac-susceptibility measurements. An implanted muon is expected to make a hydrogen bonding state with F- ions in the crystal. Muon-spin depolarization by a dynamically fluctuating component of an internal field was still observed at 30 mK. This fluctuating component is suggested to be caused by an intradimer ferromagnetic interaction of 2J(0)/k(B) = 23.3 K between radicals. No clear long-range magnetic ordering of the dimer spins was observed down to 30 mK, suggesting that the ground state of m-MPYNN . BF4 was nonmagnetic.

The crystal structure and magnetic properties of the layered perovskite, (p-chloroanilinium)(2)CuBr4 (1) have been investigated. The crystal of 1 belongs to the orthorhombic Pbca space group [a = 7.551(2) Angstrom, b = 32.082(10) Angstrom, c = 7.879(2) Angstrom, and Z = 4], which is typical of the material family. The temperature dependence of the ac susceptibility (chi(lac) = (partial derivative M/partial derivative H)) of a polycrystalline sample shows magnetic ordering at 15 K with an abrupt increase of the value. In the ordered state, the field dependence of chi(ac), namely the differential susceptibility, and the de magnetization indicate a hysteresis loop of the magnetization, which can be ascribed to the presence of spontaneous magnetization. Furthermore, single-crystal magnetic measurements indicate that the magnetic properties of 1 are quite anisotropic. When the field is along the b axis (perpendicular to the inorganic layer), the field dependence of chi(ac) shows the hysteresis behavior, as observed for the polycrystals, but when it is parallel to the a axis (parallel to the layer), chi(ac) shows metamagnetic transitions. The observed anisotropy can be understood in terms of a magnetic easy axis parallel to the a axis, an antiferromagnetic interlayer interaction, and a spin canting which produces spontaneous magnetization along the b axis.

The nuclear spin-lattice relaxation times T-1 of H-1 in organic radical salts m-MPYNN+.X-.1/3(acetone)(X = ClO4, BF4) were measured at ultra low temperatures down to 0.1 K. The T-1 in BF4 salt was almost temperature-independent below 1 K. The experimental results suggest that temperature-independent magnetic fluctuation is caused by frustration effect associated with quantum spin tunnelling in kagome antiferromagnet of S = 1 dimer. (C) 1998 Elsevier Science B.V. All rights reserved.

Low temperature properties of the organic spin-1 Kagome' antiferromagnet, m-MPYNN . BF4, have been studied by measuring heat capacity and magnetic susceptibility down to 35 mK. The heat capacity maximum due to a magnetic short-range order was observed at 1.4 K, which is about half of the antiferromagnetic interaction 2\J\/k(B)=3.1 K in the Kagome' lattice. As temperature decreases, the susceptibility begins to decrease below 0.24 K. The susceptibilities both parallel and perpendicular to the Kagome' lattice collapse to almost zero at the lowest temperature, which indicates a nonmagnetic ground state. The temperature dependence suggests that the gap energy of the magnetic state is about 0.25 K.

The crystal and magnetic structure of the 1:1 salt of Ni(dmit)(2) (dmit=1,3-dithiol-2-thione-4,5-dithiolate) anionic radical and p-EPYNN (p-N-ethylpyridinium alpha-nitronyl nitroxide) cationic radical has been studied. Ferromagnetic interaction with J/k(B)=0.16 K has been found to operate in the one-dimensional p-EPYNN chains, while the first molecular antiferromagnetic spin ladder has been found to form in the Ni(dmit)(2) chains.

We report unusual crystal structures and magnetic properties of nitronylnitroxide radical ions. (i) A nitronylnitroxide anion, p-(nitronyl nitroxide)ben to ate (p-NNBA), is found to crystallize with Mn2+ and water molecules in the form of Mn(p-NNBA)(2)(H2O)(2). In this crystal, the manganese(II) ion is in an octahedral environment, surrounded by two NO groups, two CO2 groups and two H2O. The magnetic properties are well interpreted in terms of the trimer model of [p-NNBA (S=1/2)][Mn2+ (S=5/2)]-[p-NNBA (S=1/2)]. (ii) A nitronylnitroxide cation, m-N-methylpyridinium nitronylnitroxide (m-MPYNN), crystallizes with I-, BF4-, or ClO4- into a trigonal space group, where the spin system is regarded as a spin-1 Kagome antiferromagnet with spin frustration. Low-temperature magnetic measurements reveal a spin-gap state below 0.24 K.

Intermolecular hydrogen-bonded complexes of p-nitronylnitroxide benzoic acid (p-NNBA-H) with m- and p-pyridylnitronylnitroxides (m-and p-PYNN, respectively) were prepared. The m-PYNN . p-NNBA-H complex crystallizes into the monoclinic P2(1)/c space group [a = 6.685(3) Angstrom, b = 17.657(2) Angstrom, c = 22.169(1) Angstrom, beta = 92.90(1)degrees, V = 261.3(1) Angstrom(3), Z = 4], while the crystal of p-PYNN. p-NNBA H belongs to the monoclinic P2(1)/n space group [a=12.199(3) Angstrom, b = 23.265(4) Angstrom, c = 9.522(2) Angstrom, beta = 101.84(2)degrees, V = 2644.9(9) Angstrom(3), Z = 4]. In their crystals, there is an intermolecular hydrogen bond between the nitrogen atom on the pyridyl ring of PYNN and one of the oxygen atoms of the carboxyl group of p-NNBA-H. The intermolecular N ... O distances are 2.642(5) Angstrom in m-PYNN . p-NNBA-H and 2.613(6) Angstrom in p-PYNN . p-NNBA-H, indicating rather intense hydrogen bonds. The magnetic properties of m-PYNN . p-NNBA-H and p-PYNN . p-NNBA-H are well interpreted in terms of the singlet-triplet model with 2J(AF)/k(B) = -16.0 K and the Curie-Weiss law with theta = -0.68 K, respectively.

Two cationic derivatives of alpha-nitronyl nitroxide (NN), p-PPYNN (p-N-n-propylpyridinium alpha-nitronyl nitroxide) and p-BPYNN (p-N-n-butylpyridinium alpha-nitronyl nitroxide), have been crystallized with the [Co(Pc)(CN)2](-) (dicyanophthalocyaninatocobalt(III)) counter anion. Obtained two kinds of 1:1 salt crystals have been found to be isomorphous; monoclinic, P2(1)/c, a = 15.585(6), b = 11.015(4), c = 26.111(3) Angstrom, beta = 89.95(2)degrees, V = 4482(3) Angstrom(3), Z = 4 for p-PPYNN[Co(Pc)(CN)(2)] and a = 15.830(3), b = 11.201(4), c = 25.709(3) Angstrom, beta = 90.29(1)degrees, V = 4558.4(17) Angstrom(3), Z = 4 for p-BPYNN[Co(Pc)(CN)(2)]. The magnetic interaction between the NN radicals in these two kinds of crystals has been found not to be the same; weak antiferromagnetic interaction operates in p-PPYNN[Co(Pc)(CN)(2)], while only paramagnetic behavior is observed for p-BPYNN[Co(Pc)(CN)(2)].

The complex p-NPNN . Cu(hfac)(2) (p - NPNN =p-nitrophenyl nitronylnitroxide and hfac=hexafluoroacetylacetonate) crystallizes into the triclinic P (1) over bar space group [a=12.515(3) Angstrom, b=12.540(2) Angstrom, c=11.610(3) Angstrom, alpha=106.18(2)degrees, beta=119.15(2)degrees, gamma=91.14(2)degrees, V=1501.7(6) Angstrom(3), Z=2]. The structure consists of an alternating chain of p-NPNN and Cu(hfac)(2) in which p-NPNN bridges two nonequivalent copper ions occupying the axial positions. The chains are connected by a pi-pi and head-to-tail overlap of the p-NPNN molecules, resulting in a two-dimensional network. The high-temperature magnetic susceptibilities can be interpreted in terms of a ferromagnetic intrachain interaction of J/k(B)=14.3 K and an antiferromagnetic interchain interaction of zJ'/k(B)=-2.6 K. The observed interchain interaction which would originate in the overlap of p-NPNN is much stronger than those in the related Cu(II) materials reported so far. The low-temperature magnetic susceptibilities indicate an antiferromagnetic order at T-N=1.22+/-0.01 K, followed by an enhancement of the susceptibility below T-c=0.6+/-0.1 K, probably due to a spin canting.

The HCl and DCl salts of phenyl-4-pyridyldiazomethane were prepared and irradiated at 6 K to generate the carbenes. Their ESR spectra indicated presence of plural triplet carbenes with slightly-different zero-field splitting constants. Besides the triplet species, we found a quintet species whose signal intensity decreases with increasing temperature. The quintet spin state was concluded to be a ground state which was produced by an intermolecular ferromagnetic interaction of the triplet carbenes. The ferromagnetic interaction would be explained by the McConnell mechanism, judging from the crystal structure of the HCl salt of phenyl-4-pyridylketone.

The crystal and magnetic structure of the 1:1 salt of Ni(1,3-dithiol-2-thione-4,5-dithiolate)(2) anionic radical and [Ni(dmit)(2)] p-N-ethylpyridinium alpha-nitronyl nitroxide (p-EPYNN) cationic radical have been studied. Ferromagnetic interaction with J/k(g)=0.16 K has been found to operate in the one-dimensional p-EPYNN chains, while the first molecular antiferromagnetic spin ladder has been found to form in the Ni(dmit)(2) chains.

The magnetic properties of the layered perovskite ferromagnet (p-cyanoanilinium(+))(2)CuCl42- have been studied under hydrostatic pressures up to 1 GPa. The ferromagnetic exchange gradually increases with increasing pressure and becomes 1.4 times as large at 1 GPa. The pressure dependence of the exchange constant can be semiquantitatively interpreted in terms of the shrinkage of the Cu-Cl-Cu superexchange pathway.

The crystal and magnetic structure of the 1:1 salt of Ni(Formula presented) anionic radical and [Ni(Formula presented)] (Formula presented)-ethylpyridinium (Formula presented)-nitronyl nitroxide ((Formula presented)-EPYNN) cationic radical have been studied. Ferromagnetic interaction with (Formula presented) K has been found to operate in the one-dimensional (Formula presented)-EPYNN chains, while the first molecular antiferromagnetic spin ladder has been found to form in the Ni(Formula presented) chains. © 1996 The American Physical Society.

The nuclear spill-lattice relaxation time T-1 of H-1 in the organic cation radical salt m-MPYNN(+)X(-) (S=ClO4, BF4) has been measured in the temperature range 1.5 similar to 200K and in the field range 1 similar to 70kOe. The experimental results in high fields were well interpreted in terms of flip-flop relaxation process involving the pairs of ferromagnetic dimers, whose energy scheme consists of lower triplet- and upper singlet-states with the gap energy of 20K. An appreciable increase of the relaxation rate in low fields below about 10kOe was explained by the direct relaxation process due to the band-like spread of each Zeeman level.

Organic radical cations, 4,4,5,5-tetramethyl-2-(1-methyl-3 or 4-pyridinio)-3-oxide-4,5-dihydro-1H-1-imidazolyloxyl (or, m- and p-N-methylpyridinium nitronyl nitroxides, abbreviated as m- and p-MPYNN+, respectively), were found to crystallize with magnetic counter anions, MCl4 2- (M = Mn2+ (S = 5/2) and Co2+ (S = 3/2)), although the MnCl4 2- salts were rather air-sensitive. X-Ray full-crystal analyses were carried out on the stable CoCl4 2- salts. The structure of (m-MPYNN+)2CoCl4 2- crystallizes in the monoclinic P21/c space group, while that of (p-MPYNN+)2CoCl4 2- belongs to the triclinic P1 space group. Although (m-MPYNN+)2MnCl2- 4 and (p-MPYNN+)2MnCl4 2- were not stable enough for an X-ray full data collection, they were indicated to be isostructural to the corresponding CoCl4 2- salts, respectively, by their diffractions of 20 &lt
θ &lt
25°. Variable-temperature magnetic susceptibility measurements reveal a clear contrast between the (m-MPYNN+)2MCl4 2- and (p-MPYNN+)2MCl4 2- salts. The two (m-MPYNN+)2MCl4 2- salts exhibit a ferromagnetic behavior independently of MCl4 2-, which is attributable to a m-MPYNN+ dimer. However, the magnetic properties of two (p-MPYNN+)2MCl4 2- salts are strongly dependent on the MCl4 2- anion: (p-MPYNN+)2MnCl4 2- exhibits an antiferromagnetic interaction in opposition to a ferromagnetic one in (p-MPYNN+)CoCl4 2-. The magnetic difference between them can be qualitatively understood in terms of a charge-transfer interaction between MCl4 2- and p-MPYNN+, in which the difference in the electronic structure between the Mn2+ and Co2+ ions is reflected.

(i) The magnetic properties of the series of a layered material, Cu-2(OH)(3)(n-CmH2m+1COO), are found to show an anomalous change, depending on the alkyl-chain length: the m=0 and 1 materials are metamagnetic while the m=7-9 materials become weak ferromagnets below 22 K. Further, 4-phenylazobenzoate and 2-anthracene carboxylate, which are derivatives of well-known photo-functional molecules, are intercalated into the copper hydroxides. The obtained materials are both antiferromagnetic in the whole temperature range of 3-280 K, However, the photochemical reactions do not take place by irradiation with a xenon lump. (ii) The magnetic properties of the layered perovskite ferromagnets (p-cyanoanilinium(+))(2)CuCl42- and (p-chloroanilinium(+))(2)CuBr42- are studied under hydrostatic high pressure of 1.0 GPa. Above T-c, they show an increase of the magnetization, which would due to enhancement of the ferromagnetic coupling, but, below T-c, they show different magnetic response to the pressure.

Temperature dependence of Fe-57 Mossbauer spectra for TBA[Fe(tdas)(2)] is measured to obtain the information on the spin state and the phase transitions. The large quadrupole splitting due to the S = 3/2 spin state increases reenteringly in the intermediate temperature region (190 - 230 K on cooling and 200 - 240 K on heating). The small increase in the quadrupole splitting and the continuous decrease in the isomer shift suggests the 3/2 spin state does not change, supporting the interpretation of the magnetic susceptibility.

Reaction of m- or p-pyridyl nitronyl nitroxide (m- or p-PYNN) with HBr gas gave a 2:1 complex between them. The IR spectra of (m- and p-PYNN)(2)HBr indicates an intermolecular [NHN](+) hydrogen bond between two pyridyl rings. (m-PYNN)(2)HBr shows ferromagnetic properties, while the p-isomer does antiferromagnetic properties. Furthermore, the HCl salt of phenyl-4-pyridylcarbene was generated by irradiation of the diazo precursor. The ESR spectrum shows signals of triplet and quintet spin species, latter of which indicates a ferromagnetic interaction between the triplet carbenes.

Crystal structures and magnetic properties of the layered pervoskite compounds, (p-X-C6H4NH3+)(2)CuCl42- with X=CN (1), Cl (2), and NO2 (3), were studied. The compound 1 crystallizes in the triclinic &lt;P(1)over bar&gt; space group. The structure consists of a CuCl layer and an organic bilayer in which the molecular axis of the cyanoanilinium is nearly perpendicular to the inorganic layer. At the middle of the organic bilayer, there is a layer of the CN group, in which the CN groups are arranged to cancel their electric dipoles. The compound 2 has a similar structure to that of 1. The crystal of 3 belongs to the orthorhombic Pbca space group, in which the structure also consists of an inorganic layer and an organic bilayer. The bilayer is formed by short contacts between the NO2 groups, which appear to incline the molecular axis of the nitroanilinium with respect to the normal to the CuCl layer. AC and DC magnetic susceptibility measurements were carried out on the three salts. Their behavior can be understood with two parameters, ferromagnetic transition temperature T-c and in-plane ferromagnetic coupling constant J. The obtained parameters are T-c=9.5 K and J/k(B)=24 K for 1, T-c=9.1 K and J/k(B)=23 K for 2, and T-c=7.0 K and J/k(B)=17 K for 3. The values of T-c and J of 3 are smaller than those of the other two. The distortion of the molecular arrangement in the organic layer of 3, is found to result in weakening the magnetic interaction in the CuCl layer.

EPR measurements were carried out on a single crystal of m-N-methylpyridinium nitronyl nitroxide perchlorate which consists of a 2-D bond-alternated hexagonal lattice. Angular dependence of the linewidth Delta H-pp shows minimums at the magic angles, and can be well interpreted with the theoretical equation for the 2-D magnetic system,Delta H-pp=A(3cos2 theta . 1)(2)+B. Temperature dependence of Delta H-pp shows an anomaly between 50 K and 100 K, which could be relevant to freezing of the orientational disorder of the perchlorate ion. Angular dependence of the g-value confirms the 2-D character of the magnetic system. Below 50 K, the EPR signal is affected by the demagnetizing effects.

Crystal structures and magnetic properties of m-N-methylpyridinium nitronyl nitroxide (abbreviated as m-MPYNN+) salts were studied. m-MPYNN+. ClO4-.(1/3)(acetone) is found to crystallize into the trigonal P3c1 space group, where the m-MPYNN+ molecules exist as a dimer and the dimer units form a 2-D triangular lattice. Temperature dependence of the magnetic susceptibility can be well interpreted in terms of a strong ferromagnetic intradimer interaction J(1) forming a triplet state and a weak antiferromagnetic interdimer interaction J(2). There is a possibility that this spin system can be characterized as a spin-1 Kagome antiferromagnet at very low temperatures. m-MPYNN+ makes salts with various anions, I-, Cl-, BF4-, ClO4- etc. and their mixtures. In an isostructural solid-solution system, m-MPYNN+.(ClO4-)(x) . l-(1-x).(1/3)(acetone) (0 less than or equal to x less than or equal to 1), J(2) quickly weakens with increasing the ratio of the ClO4- ion, in contrast to little dependence of J(1).

The magneto-structural correlation in some p-N-alkylpyridinium nitronyl nitroxide salts has been studied. In the iodide salts of p-N-R-pyridinium nitronyl nitroxides with R=methyl, ethyl, n-propyl, and n-butyl, the magnetic property varies from antiferromagnetic to ferromagnetic with the extension of the N-alkyl chain. The nearest-neighbor molecular arrangements of the nitroxides observed in the four crystals, can be classified into two groups: the radicals are connected by a intermolecular contact between the NO groups (Type I) or between the NO group and the pyridinium ring (Type II). The observed magnetic behaviors can be interpreted in terms of an antiferromagnetic intermolecular interaction for the Type I contact and a ferromagnetic for Type II. Effects of replacement of the I- ion by Br- or Cl-, have been also studied in the p-N-methyl derivative.

In this paper we study an organic system of geometrical spin frustration. m-N-methylpyridinium alpha-nitronyl nitroxide (m-MPYNN+) is a spin-1/2 organic radical. The simple salt, m-MPYNN+.ClO4-.1/3 (acetone), crystallizes in a trigonal P3c1 space group, where the m-MPYNN+ molecules exist as a dimer and the dimer units form a two-dimensional (2D) triangular lattice. One-third of the ClO4- ions are in the organic layer, joining the m-MPYNN+ molecules, and the remainder is between the layers, compensating the excess of positive charge in the organic layers. The single-crystal EPR measurements clearly indicate a 2D Heisenberg character of the magnetic system in it. m-MPYNN+ makes a crystalline solid-solution system, m-MPYNN+.(ClO4-)x.I1-x-.1/3 (acetone) (0 less-than-or-equal-to x less-than-or-equal-to 1), which also belongs to the trigonal system. Both the a and c axes are slightly lengthened with increasing the ratio of the ClO4- ion, x, in the solid solution: The unit-cell volume is increased by 3.2% when x runs from 0 to 1. The temperature dependence of the magnetic susceptibilities of the solid solutions can be well interpreted in terms of a strong ferromagnetic intradimer interaction J1 forming a triplet state and a weak antiferromagnetic interdimer interaction J2 which is expected to give rise to spin frustration among the triplet spin species on each side of the triangles. It is found that J2 quickly weakens with an increase in x, while J1 shows little dependence. There is a possibility that this organic system can be characterized as a spin-1 kagome anti-ferromagnet at very low temperatures.

Reaction of 2-(3-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1- oxyl 3-N-oxide (m-PYNN) and HBr gas gives rise to the complex (m-PYNN) 2HBr, in which the coexistence of an intermolecular ferromagnetic interaction and an [NHN]+ hydrogen bond is found.

Magnetic measurements and X-ray crystal analyses were carried out on iodide salts of p-N-alkylpyridinium a-nitronyl nitroxides [4-(4,4,5,5-tetramethyl-1-oxido-3-oxyl-4,5-dihydro-3H-imidazol-2'yl)-1-R-pyridinium, with R = methyl (1(+)), ethyl (2(+)), n-propyl (3(+)) and n-butyl (4(+))]. The strongly antiferromagnetic crystal of 1(+).l(-) consists of a radical dimer and the iodide ion is out of the plane of the pyridinium ring. 2(+).l(-), which is weakly antiferromagnetic, includes two crystallographically independent molecules, 2A(+) and 2B(+), each of which forms a centrosymmetric dimer. in the pyridinium ring of 2A(+) the iodides are 'out-of-plane' while for 2B(+) they are 'in-plane'. The ferromagnetic 3(+).l(-) and 4(+).l(-) have similar structures: the crystal consists of a two-dimensional (2D) layer formed by a contact between the pyridinium ring and in-plane iodides. In this series, the iodide ion changes position from out-of-plane to in-plane and the magnetism varies from antiferromagnetic to ferromagnetic. It is found that the nitronyl nitroxide with an out-of-plane iodide has a short intermolecular contact between the NO groups (type I), while that with an in-plane iodide forms a contact between the NO group and the pyridinium ring (type II). The observed magnetic behaviour can be interpreted in terms of an antiferromagnetic interaction for the type I contact and a ferromagnetic interaction for type II.

In this paper we study an organic system of geometrical spin frustration. m-N-methylpyridinium α-nitronyl nitroxide (m-MPYNN+) is a spin-1/2 organic radical. The simple salt, m-MPYNN+ClO4-1/3 (acetone), crystallizes in a trigonal P3c1 space group, where the m-MPYNN+ molecules exist as a dimer and the dimer units form a two-dimensional (2D) triangular lattice. One-third of the C1O4- ions are in the organic layer, joining the m-MPYNN+ molecules, and the remainder is between the layers, compensating the excess of positive charge in the organic layers. The single-crystal EPR measurements clearly indicate a 2D Heisenberg character of the magnetic system in it. m-MPYNN+ makes a crystalline solid-solution system, m-MPYNN+(ClO4-)xI1-x-1/3 (acetone) (0≤x≤1), which also belongs to the trigonal system. Both the a and c axes are slightly lengthened with increasing the ratio of the C1O4- ion, x, in the solid solution: The unit-cell volume is increased by 3.2% when x runs from 0 to 1. The temperature dependence of the magnetic susceptibilities of the solid solutions can be well interpreted in terms of a strong ferromagnetic intradimer interaction J1 forming a triplet state and a weak antiferromagnetic interdimer interaction J2 which is expected to give rise to spin frustration among the triplet spin species on each side of the triangles. It is found that J2 quickly weakens with an increase in x, while J1 shows little dependence. There is a possibility that this organic system can be characterized as a spin-1 kagomé antiferromagnet at very low temperatures. © 1994 The American Physical Society.

Nematic phase polymerization of diacetylenes proceeded without an induction period. The decay rate of monomers was found to be enhanced in a thin film sample. When an external electric field was applied to the thin film, the rate was accelerated with a threshold value of 2500 V/cm which corresponds to that for a dynamic scattering mode.

Novel unsymmetrically aryl-substituted diacetylene derivative (1), 4'-(5''-hydroxy-1'',3''-pentadiynyl)benzylidene-p-anisidine, was prepared. Reactivity of polymerization of 1 in the solid state was discussed based on its crystal structure revealed by an X-ray diffraction method.

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