Solvent-controlled synthesis of an Al12-oxo molecular ring and Al24-oxo truncated metallo-cube

Abstract

Highly symmetrical molecules with beautiful geometries are ubiquitous in nature. It has inspired creative ideas of the perfect combination of geometry and molecular structural chemistry. Some metal clusters with regular geometric polyhedra have been reported, but such highly symmetric polyhedra for Al-oxo clusters are really scarce on account of the fast hydrolysis of Al³⁺ ions. Herein, a [Al₁₂(CH₃O)₂₄(NAP)₁₂]·4DMF·2H₂O·2CH₃OH (Al₁₂, NAP⁻ = 2-naphthoic acid) nanoring was synthesized by the solvothermal reaction of AlCl₃·6H₂O, 2-naphthoformic acid (HNAP) and triethylamine (Et₃N) in CH₃OH and DMF. Interestingly, the regulation from ring-shaped Al₁₂ to [Al₂₄(OH)₃₂(CH₃O)₂₂(CH₃OH)₂(NAP)₁₂]·6Cl·2H₂O·2CH₃OH (Al₂₄) metallocage is realized by only changing the reactive solvents. The Al₂₄ metallocage can be seen as one of 13 Archimedean polyhedra, a truncated cube composed of eight Al₃ triangles and six Al₈ octagons by sharing vertical Al³⁺ ions. In addition, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) reveals that the metallic skeletons of Al₁₂ and Al₂₄ can be maintained stable in CH₃OH and CH₂Cl₂. Furthermore, Al₁₂ and Al₂₄ emit blue luminescence and exhibit photocurrent responses under LED light illumination.