Polynuclear chromium(III) carboxylates. 3. Cyclic and cubane type hexachromium acetates |
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Authors: | Michal EshelAvi Bino |
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Affiliation: | Department of Inorganic and Analytical Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel |
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Abstract: | Heating an aqueous solution of the trinuclear ‘basic’ chromium(III) acetate led to the formation of several products which were separated by ion-exchange chromatography. Crystals of a new cyclic, hexanuclear Cr(III) compound, [Cr6(OH)10(O2CCH3)6(H2O)4]Cl2·13H2O (3·Cl2·13H2O) were obtained upon elution of the violet complex 3 with 0.5 M NaCl and slow evaporation of the eluent. The six chromium atoms in complex 3 form an almost planar, irregular hexagon with an overall symmetry close to C2h. By heating solid ‘basic’ chromium(III) acetate at 300 °C, followed by ion-exchange separation, a new hexanuclear complex, [Cr6O3(OH)(O2CCH3)9(H2O)4]2+ (4) has been obtained. Complex 4 has a {Cr6O4} core, which consists of a {Cr4O4} cubane type inner core with two external chromium centers attached to μ4-oxo(cube) ligands. A similar procedure, using ‘basic’ chromium(III) propionate led to the isolation of the dodecanuclear complex [Cr12O8(O2CCH2CH3)16(H2O)8]4+ (5) which has a {Cr12O8} core. The {Cr6O4} core in complex 4 can be regarded to be formed from a tetranuclear {Cr4O2} butterfly unit and a dinuclear {Cr2O2} unit. Similarly, the {Cr12O8} core in 5 can be considered to be constructed from two orthogonal {Cr6O4} units as in complex 4. |
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Keywords: | Crystal structures Chromium complexes Polynuclear complexes |
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