In situ observations of the phase transition among cobalt(II) dichloride hydrates and crystal structures of the tetra- and hexahydrates.
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概要
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Transformation among cobalt(II) dichloride hydrates in aqueous solutions was studied by the optical microscopic method. Although there are three hydrates (CoCl<SUB>2</SUB>·6H<SUB>2</SUB>O, CoCl<SUB>2</SUB>·4H<SUB>2</SUB>O, and CoCl<SUB>2</SUB>·2H<SUB>2</SUB>O) in the phase equilibrium diagram, the only solution mediated transformation between CoCl<SUB>2</SUB>·6H<SUB>2</SUB>O and CoCl<SUB>2</SUB>·2H<SUB>2</SUB>O could be observed under the present experimental conditions and it was confirmed that CoCl<SUB>2</SUB>·4H<SUB>2</SUB>O hardly formed compared with the other two hydrates. In order to investigate the reason why CoCl<SUB>2</SUB>·4H<SUB>2</SUB>O was hardly crystallized at the transformation from CoCl<SUB>2</SUB>·6H<SUB>2</SUB>O through CoCl<SUB>2</SUB>·2H<SUB>2</SUB>O and vice versa, the crystal structure of CoCl<SUB>2</SUB>·4H<SUB>2</SUB>O was investigated by the X-ray diffraction method. The structure of CoCl<SUB>2</SUB>·6H<SUB>2</SUB>O was reexamined because previously reported results had a relatively large <I>R</I>-factor. The crystal of CoCl<SUB>2</SUB>·4H<SUB>2</SUB>O is monoclinic, space group <I>P</I>2<SUB>1</SUB>/<I>a</I> with <I>a</I>=11.548(1) Å, <I>b</I>=9.342(1) Å, <I>c</I>=6.056(1) Å, β=110.79(1)°, and <I>Z</I>=4. The complex has a slightly distorted octahedral geometry about Co<SUP>2+</SUP> ion and two Cl<SUP>−</SUP> ions are located at the cis-position. The crystal of CoCl<SUB>2</SUB>·6H<SUB>2</SUB>O is monoclinic, space group <I>C</I>2/<I>m</I> with <I>a</I>=10.380(2) Å, <I>b</I>=7.048(1) Å, <I>c</I>=6.626(1) Å, β=122.01(1)°, and <I>Z</I>=2. The geometry around the cobalt ion is also octahedral with four water molecules and two chloride ions at the equatorial and the axial positions, respectively. The remaining two water molecules are linked to the two Cl<SUP>−</SUP> ions by hydrogen bonding. The difficulty of crystallization of CoCl<SUB>2</SUB>·4H<SUB>2</SUB>O crystals in solutions was explained in terms of the relatively unstable cis-dichloro structure of the [CoCl<SUB>2</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>] moiety and its crystal structure stabilized by hydrogen bonding network between the cis-form moieties.
- 公益社団法人 日本化学会の論文
著者
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Ohtaki Hitoshi
Coordination Chemistry Laboratories Institute For Molecular Science
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Sunagawa Ichiro
Institute Of Mineralogy Petrology And Economic Geology Faculty Of Science Tohoku University
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Tsukamoto Katsuo
Institute Of Mineralogy Petrology And Economic Geology Faculty Of Science Tohoku University
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Masuda Hideki
Coordination Chemistry Laboratories, Institute for Molecular Science
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Waizumi Kenji
Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University
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