Single-crystal magnetic susceptibility and specific heat studies of the one-dimensional copper complex [PM·Cu(NO3)2·(H2O)2]n (PM = pyrimidine) show that it behaves like a uniform S = 1/2 antiferromagnetic Heisenberg chain, characterized by the exchange parameter J/kB = 36 K. Specific heat measurements in the applied magnetic field, however, reveal the formation of a field-induced spin excitation gap, whose magnitude depends on the magnitude and direction of the field. This behaviour is inconsistent with the ideal S = 1/2 Heisenberg chain. In the low-temperature region, a contribution to the susceptibility, approximately proportional to 1/T, is observed which varies strongly with the varying direction of the magnetic field. The field-induced gap and the 1/T contribution are largest for the same field direction. Previous observations of a field-induced gap in the related compounds copper benzoate and Yb4As3 have been explained by the alternating g tensor and alternating Dzyaloshinkii-Moriya interaction, producing an effective staggered magnetic field at the Cu and Yb ions. We apply this model to [PM·Cu(NO3)2·(H2O)2]n and obtain a consistent quantitative explanation of the low-temperature susceptibility, the field-induced gap and their dependence on the magnetic-field direction.

A metal-radical polymer [Co(hfac)2.BPNN] showed a very large coercive field of 52 kOe (4.1 MA m-1) at 6 K, indicating that it is the hardest magnet ever reported. Above 10 K, a soft character appeared, owing to the fast dynamics of magnetization reorientation.

Lanthanide ions are supposed to be promising candidates for the elements of single-molecule magnets (SMMs) because of the large magnetic momentum and anisotropy. We have established the [Dy2Cu] complex as a new SMM. A plausible mechanism for quantum tunneling of magnetization is proposed for the first time among the 4f-3d heterometallic SMMs. The magnetic coupling parameter between Dy and Cu ions was well-defined as -0.155 K.

The title trinitroxide 4 was synthesized via the bis[m-(hydroxyamino)phenyl] nitroxides 9 and 10. The ESR spectra obtained in a toluene glass at 4.2 K was consistent with 4 in a quartet state with the zfs parameter ID(/hu of 0.0087 cm-'. The quartet state was shown to be the ground state by the magnetic measurement of its microcrystalline sample on a Faraday balance. The maximum of the effective moment was 3.53 pg at ca. 140 K. The Weiss constant and the energy gap between the lowest excited doublet and the ground quartet states were estimated to be -19 and +240 K, respectively.(7) Corey, E. J.; Venkateswarlu, A.

The cycloadducts of CG0 and typical dienes have been isolated by HPLC, and the anthracene and cyclopentadiene adducts characterized by FAB mass and NMR spectroscopy.Studies on fullerenesl have been extensive since the macroscopic synthesis of fullerenes was discovered in 1990.2 It is important to study the chemical reactivity of fullerenes,3.4 in order to gain fundamental knowledge for the development of fullerene derivatives with interesting physical and chemical properties. This paper reports the syntheses, isolation and characterization of several cycloadducts of C a with anthracene, cyclopentadiene, 1,3-diphenylisobenzofuran and 2,3-dimethylbutadiene. Although Diels-Alder reactions of c 6 0 have been reported recently by some groups,S-7 they mentioned that mass spectral characterization of the adducts was hampered by fragmentation into component molecules. Rubin et al. also reported that the reaction products between anthracene and C a could not be isolated and characterized. 6 We have now found that the Diels-Alder adducts of c 6 0 with anthracene or cyclopentadiene can be characterized unequivocally by means of negative ion FAB mass and 1H and 13C NMR spectroscopy.The addition reaction of c 6 0 with anthracene is typical. A mixture of C60 (18 mg), anthracene (5.4 mg) and benzene (5 ml) was refluxed for 12 h under nitrogen. After evaporation under reduced pressure below 50°C, the products were separated by HPLC (LC 908, Japan Analytical Industry, Co., Ltd.) by using gel permeation columns (Jaigel 1H + 1H) and toluene as eluent, to give 5.6 mg (25%) of the mono-adduct Cm(Cl4HI0) and 6.4 mg (24%) of di-adducts C60(C14H10)2.

Multifunctional π-expanded macrocyclic oligothiophene 6-mer 1, as well as 9- (2) and 12-mers (3), was synthesized using a McMurry coupling reaction as the key step. The 6-mer 1 was converted to cyclo[6](2,5-thienylene-ethynylene) (4) by using a bromination-dehydrobromination procedure. From X-ray analysis, the crystal structures of nonplanar 1 and round-shaped 2 and 4 were elucidated. STM showed that 4 formed a self-assembled monolayer at the liquid/solid interface to produce a hexagonal porous network. Chemical oxidation of 1, 2, and 4 with 1 and 2 equiv of Fe(ClO4)3 produced 1(•+) and 1(2+), 2(•+) and 2(2+), and 4(•+) and 4(2+), respectively. Although oligothiophene radical cations containing β,β-disubstituted thiophenes usually do not form π-dimers, 4(•+) clearly formed a π-dimer owing to its planar, round shape. As for the dications of 1, 2, and 4, 1(2+), which has 34π-electrons, exhibited a large diatropic ring current effect, whereas 34π dication 4(2+) only showed a medium diatropic ring current effect. In contrast to 1(2+) and 4(2+), 52π dication 2(2+) had biradical cationic character instead of Hückel-type cyclic conjugation. Interestingly, 6-mer 1 showed polymorphism and unusual melting point behavior due to the number of stable conformations in the solid state. Single crystals of 1 melted at 176 °C, whereas an amorphous film of 1 crystallized in the temperature range of 80-83 °C to form a lamellarly stacked microcrystalline film, which melted at 139 °C. The polymorphism of 1 was applied to either fluorescence switching or switching of field effect transistor (FET) activity and electrical conductivity.

Two novel copper(II) complexes with tert-butyl 2-pyridyl nitroxide (2pyNO(*)), [Cu(2+)(2pyNO(-))(2pyNO(*))](2)(BF(4)(-))(2) (1 x BF(4)) and [Cu(2+)(2pyNO(-))(2pyNO(*))](2)(ClO(4)(-))(2) (1 x ClO(4)), were prepared and structurally characterized. They contained mixed-valent ligands from 2pyNO, whose oxygen atoms were located at equatorial positions of the copper ion. The [Cu(2+)(2pyNO(-))(2pyNO(*))] unit was dimerized by mu-oxo bridges of the anion ligand, giving a zigzag linear spin system involving four paramagnetic S = 1/2 centers. The two compounds are isomorphous in an orthorhombic Pbca space group. Magnetic study revealed that 1 x ClO(4) showed ferromagnetic copper-radical coupling in all temperature ranges investigated here. On the other hand, 1 x BF(4) exhibited a structural phase transition at 64 K, where the magnetic susceptibility was drastically dropped on cooling. The copper-radical magnetic couplings were characterized as ferro- and antiferromagnetic for the high- and low-temperature phases, respectively. The crystallographic analysis clarified that the nitroxide oxygen atom remained at the equatorial position throughout the single-crystal-to-single-crystal phase transition, while the previously known spin-transition-like copper-radical compounds showed conversion of the roles of equatorial and axial positions. The orthogonal arrangement between the copper d sigma and nitroxide pi* orbitals is essential for the ferromagnetic coupling, and a slight dislocation of the radical oxygen atom from the chelate plane leads to violation of the orthogonal orbital arrangement, giving a practically diamagnetic low-temperature phase.

No abstract