We calculate the electronic states of the Mn-doped semiconductors and show that resonant states are formed at the top of the down spin valence band due to magnetic impurities and that they give rise to a strong and long-ranged ferromagnetic coupling between Mn moments. We propose that the coupling of the resonant states, in addition to the intra-atomic exchange interaction between the resonant and nonbonding states, is the origin of the ferromagnetism of (Ga-Mn)As. The mechanism is thus called "double resonance." The resonant states bring about the spin-dependent resistivity to produce magnetoresistive properties in (Ga-Mn)As and their junctions.

The spatial distribution of the nonequilibrium current in a series of two point contacts under a finite bias voltage is investigated numerically making use of a recursive Green-function method based on the Keldysh formalism. The results of the current distribution show an interesting behavior such as the existence of vortices in between the two barriers. The temperature dependence of the nonlinear current-voltage characteristic is also studied. ͓S0163-1829͑98͒02216-4͔

The first highly-resolved 19F n.m.r. spectra in the gas-phase have been observed for 1,2-difluoroethane, and the conformational energy difference between the gauche and trans states has been estimated to be about -0.8 kcal/mol (1 kcal = 4.184 kJ) from the coupling constants observed in the 19F and l H n.m.r. spectra.

The effect of on-site Coulomb repulsion on the process of resonant tunneling is studied in the tightbinding model of a quasi-one-dimensional system. The conductance through a small region where the Coulomb interaction is strong is calculated as a function of chemical potential with use of the Kubo formula. The Green's function and the number of electrons in the region are obtained self-consistently using the recursion method in the mean-field approximation. It is found that the conductance shows various doublet structures depending on the broadening of the virtual bound state and the Coulomb interaction.

Substitution-inert cobalt(II1) complexes containing an N-glycoside formed from ethylenediamine (en) and an aldose (o-mannose, L-rhamnose, or D-ribose) were synthesized by the oxidation of cobalt(l1) to cobalt(II1) in the presence of the diamine. It was found that [(en)2Co(02)(OH)Co(en)2]3+ is a reactive species toward aldoses in the reaction. The major product for each starting aldose was purified by column chromatography to yield red crystals. The isolated complexes were characterized by elemental analysis, conductivity measurements, and IH and I3C NMR, electronic absorption, and circular dichroism spectroscopies, the results of which show that the complexes are composed of a bidentate en and a tetradentate N-glycoside ligand. The structures of the sugar units were analyzed by means of the semiempirical AM1 calculations coupled with the conversion of the vicinal 'H-IH spin-spin coupling constants in the IH N M R spectra into torsion angles of the corresponding H-C-C-H fragments. The results of the calculations demonstrate that the D-mannose and L-rhamnose units take the pyranose form with the p-3S5 skew-boat conformation on the cobalt(II1) complexes, while the D-ribose unit adopts the furanose form with the w 2 E envelope conformation on the complex; in addition the sugar units of the N-glycoside ligands facially bind to the cobalt atom at three points through the donor atoms on CI, C2, and C3. The interaction of sugars with various metal ions is well-known and is of current interest in bioinorganic chemistry in connection with metal-containing enzymes and industrial applications. Despite such a wide interest, very little is systematically known about the structural details of sugar-metal complexes.2-6In order to elucidate the interaction between sugars and transition metals, we have extensively studied the synthesis and characterization of substitution-labile nickel(I1) complexes containing N-glycoside(s) derived from the reaction of sugars and diamines.'-'' During a series of our investigations about Nglycoside systems formed from an aldose and a diamine with primary amino groups such as ethylenediamine or tri-methylenediami~~e,'-~ the structures of [ N i (~-G l c N -e n '~)~] Br,. 4 H 2 0 * and [N~(L-R~~-~~'~),]B~~.~H~O.CH~OH~ were determined ( I ) Present address: (aTakizawa, S.; Sugita, H.; Takahashi, T.; Tsubomura, T.; Shioi, H.; Yoshikawa, S. Curbohydr. Res. 1985, (8) Yano, S.; Sakai, Y.; Toriumi, K.; Ito, T.; Ito, H.; Yoshikawa, S. Inorg. Chem. 1985. 24, 498-504. (9) Shioi, H.; Yano, S.; Toriumi, K.; Ito, T.; Yoshikawa, S. J . Chem. SOC., Chem. Commun. 1983, 201-202.