Competitive coordination aggregation for V-shaped [Co3] and disc-like [Co7] complexes: synthesis, magnetic properties and catechol oxidase activity.

Unique dependence on the nature of metal salt and reaction conditions for coordination assembly reactions of varying architecture and nuclearity have been identified in V-shaped [Co₃L₄] and planar disc-like [Co₇L₆] compounds: [CoII3L₂(μ-L)₂(μ-OH₂)₂(CF₃CO₂)₂] (1) and [CoII7(μ-L)₆(μ-OMe)₆]Cl₂ (2) (HL = 2-{(3-ethoxypropylimino)methyl}-6-methoxyphenol). At room temperature varying reaction conditions, cobalt-ligand ratios and use of different bases allowed unique types of coordination self-assembly. The synthetic marvel lies in the nature of aggregation with respect to the two unrelated cores in 1 and 2. Complex 1 assumes a V-shaped arrangement bound to L⁻, water and a trifluoroacetate anion, while 2 grows around a central Co^II ion surrounded by a {CoII6} hexagon bound to methoxide and L⁻. Magnetic measurements revealed that the intermetallic interactions are antiferromagnetic in nature in the case of complex 1 and ferromagnetic in the case of 2 involving high spin cobalt(ii) ions with stabilization of the high-spin ground state in the latter case. In MeCN solutions complexes 1 and 2 showed catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH₂) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in air. The kinetic study in MeCN revealed that with respect to the catalytic turnover number (k_cat) 2 is more effective than 1 for oxidation of 3,5-DTBCH₂. [ABSTRACT FROM AUTHOR]