| Research Abstract |
We succeeded in the preparation of good single crystals of a microporous crystal AlPO_4-5 having a micropore with a circular cross section of 7.3 A. To prepare one-dimensional molecular chains enclosed in this micropore, we tried to intercalate p-benzoquinone and hydroquinone molecules into AlPO_4-5 crystals. Using obtained single crystals of AlPO_4-5 contained these molecules we measured polarized IR and Raman spectra, ESR, NMR and electronic spectra at various temperature down to 4 K. From IR spectra, it was shown that the molecular axes in benzoquinone molecules are placed perpendicular to the pore direction. On the other hand, ESR spectra showed the formation of benzoquinone radicals in micropores, and a new fact that these anion radical orient with their molecular axes parallel to the 1-D pore direction.
In AlPO_4-5 intercalated hydroquinone molecules, molecular orientations in micropores were shown to be analogous to benzoquinone, but when intercalated more hydroquinone molecules, more radicals were shown from ESR measurements, and the crystal color which was originally white was changed and became blue greenish close to that of quinhydron. Our analysis of vibrational spectra in IR and Raman measurements revealed that hydroquinone molecules are oxidized in the micropores and the presence of semiquinone radicals and finally benzoquinone molecules was observed.
These remarkable results taking place in micropores were explained by chemical reactions occurring on the wall of micropores, and in these reactions oxygen in the air plays an important role for oxidation. The obtained orientations of molecules and radicals were explained by electrostatic interactions of π and σ electrons in molecules and oxygen atoms on the wall. In the hydroquinone system, it is expected that some kind of intermolecular electron transfers along the one-dimensional molecular array take place in the micropores.
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