pH and molar ratio dependent formation of monomeric,dimeric and tetrameric cobalt malate complexes |
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| Authors: | Qiong-Xin Liu Lu-Bin Ni Fu-Pei Liang Zhao-Hui Zhou Hui-Lin Wan |
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| Institution: | 1. College of Chemistry and Chemical Engineering, State Key Laboratory of Physical Chemistry of Solid Surface, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, Xiamen University, Xiamen 361005, China;2. College of Chemistry and Chemical Engineering, Guangxi Normal University, Guilin 541004, China |
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| Abstract: | The reactions of cobalt(II) chloride with racemic malic acid (H3mal = C4H6O5) result in the isolation of monomeric, dimeric and tetrameric cobalt malato complexes: (NH4)2Co(R-Hmal)(S-Hmal)] · 2H2O (1), Co2(R-Hmal)(S-Hmal)(H2O)4]n · 2nH2O (2), K4Co4(OH)2(R-mal)2(S-mal)2(H2O)4] · 10H2O (3) and trans-Co(R-H2mal)(S-H2mal)(H2O)2] · 2H2O (4). The formations of the malato complexes are dependent on the pH value, the molar ratio of the solutions, the reaction temperature and the counterions. In the water-soluble compound 1, the CoII ion is octahedrally coordinated by two tridentate malates via their α-hydroxy, α-carboxy and β-carboxy groups. The malate ligands in 2 coordinate with the cobalt ion via their α-hydroxy and α-carboxy groups, while the β-carboxy group acts as a bridging ligand for the other two cobalt ions, forming a novel dimeric unit Co2(R-Hmal)(S-Hmal)(H2O)4], which further connects into a layered structure through links from the oxygen atoms of the β-carboxy groups. Complex 3 is a tetranuclear mixed-valence species. Both of the CoII ions exist in trans-Co(R-mal)(S-mal)(H2O)2] units, which are linked by a CoIII2(OH)2 unit with bridging α-alkoxy and β-carboxy groups. Compound 4 is the main product of reaction between cobalt chloride and excess malate under weakly acidic conditions. |
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| Keywords: | Cobalt Malic acid X-ray crystal structure Tetramer Mixed-valence complex Coordination polymer |
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