Assembly of {Co14} nanoclusters from adenine-modified Co4-thiacalix[4]arene units

Abstract

Three cobalt-thiacalix[4]arene coordination clusters, namely, {[Co₁₄(T4A)₃(AD)₆(HAD)₂Cl₇(HCOO)₃](DMF)₄(H₂O)}[+solvent] (Co₁₄α), {Co₁₄(T4A)₃(AD)₆Cl₄(HCOO)₆(H₂O)}[+solvent] (Co₁₄β), and {Co₁₄(T4A)₃(AD)₆(OH)₃(CH₃COO)₇(H₂O)₂}[+solvent] (Co₁₄γ) (H₄T4A = p-H-thiacalix[4]arene, HAD = adenine), were prepared with a solvothermal self-assembly method by changing the reaction conditions. In these structures, the adenine-functionalized Co₄-T4A entity is a common secondary building unit (SBU). The cluster Co₁₄α is formed from two Co₄(T4A)Cl(HCOO)(AD)₂ units and one Co₄(T4A)Cl(HCOO)(HAD)₂ unit, all three being linked into an unsymmetrical triangular array by two additional triply bridging AD⁻ ligands, with the two Co₄(T4A)Cl(HCOO)(AD)₂ units being further bridged by {CoCl₂} entities bound to their AD⁻ ligands. The cluster Co₁₄β, obtained from a different solvent mixture, is a trigonal cage formed from three Co₄(T4A)Cl(HCOO)₂(AD)₂ units linked by imidazolate-N coordination to {CoCl/H₂O} bridgeheads. Substitution of DMA for the DMF co-solvent results in a similar trigonal cage, Co₁₄γ, but it is of lower symmetry and formed from two Co₄(T4A)(OH)(CH₃COO)₂(AD)₂ units and one Co₄(T4A)(OH)(CH₃COO)(H₂O)₂(AD)₂ unit linked by imidazolate-N coordination to two Co(CH₃COO) bridgeheads.