| Research Abstract |
The electron-density distributions of organic radical crystals and transition-metal complexes have been investigated using X-ray diffraction data measured at 100 K.Deformation electron-density distributions were calculated from the structure factors refined by the multipole expansion method.
1. Some of the 4-Ar-CH=N-TEMPO radicals (TEMPO=2,2,6,6-tetramethylpiperidyl-1-oxyl), showed intermolecular ferromagnetic interactions at an extremely low temperature. In these crystals, the ferromagnetic interactions are transferred through O--- H van der Waals' interactions of beta-H atoms of the neighboring TEMPO rings. From the electron-density distributions, it was suggested that the unpaired electron of the 0 radical atom was located on the of the N-O bond. The beta-H atoms of the neighboring TEMPO rings contact with the 0 atom from the directions to avoid the lonepairs of the O atom and to prefer to the pi*-orbital.
2. An unusually long radical N-O bond and a short intermolecular & O-O contact
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were observed in the crystals of 6,6-bis-(p-tolyl)-5,6-dihydro-phenanthridin-N-oxyl from the batch I . In the D-maps, significant peaks were observed on the O-O line. From the detailed refinements, a disordered structure, which contained a radical N-O bond and N-O-H bond forming an intermolecular O-H O hydrogen bond, were obtained, In the crystals from the batch II, the molecules showed the geometry of typical radicals, not showed a disordered structure. It is very interesting that the structure of the pure radical crystals are isomorphous with those constructed by the hydrogen-bonding.
3. The electron density distributions of [Cu(II)(NO_3) _2 (pm) _3] (1) (ferromagnetic interaction) and [Cu(II)(NO_3)_2(pm)_2(H_2O)_2] (2) (antiferromagnetic interaction) (pm=pyrimidine) were investigated. The Cu atom in 1 is coordinated square pyramidally by two 0 atoms and three N atoms. In 2, it is coordinated octahedrally by four 0 atoms and two N atoms. For 2, six peaks are observed around the Cu atom, which show 3d electrons. Electron densities for lone-pairs of ligands are also clearly observed. Less
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