Self-assembly and host–guest chemistry of big metallosupramolecular M4L4 tetrahedra

Abstract

Metallosupramolecular tetrahedra M₈[L₄Ti₄] are easily obtained by self-assembly from the triangular ligands L-H₆ and titanoyl bis(acetylacetonate) in the presence of alkali metal carbonates as base. All the complexes can be well characterized by ¹H NMR in combination with ESI FT-ICR MS. Force field calculations reveal that the tetrahedra show Ti–Ti separations of 17 Å ([L¹₄Ti₄]⁸⁻) and 23.5 Å ([L²₄Ti₄]⁸⁻), respectively, leading to huge internal cavities. The cavity is readily shielded in the case of L¹ but possesses big pores with the bigger ligand L². [L¹₄Ti₄]⁸⁻ was used to investigate the host–guest chemistry of these container molecules and it was found that cationic organic guest species like anilinium can be introduced in the interior of the complex. Inclusion is nicely followed by NMR spectroscopy. Upon addition of one equivalent of guest the symmetry of the tetrahedron is lost but is regained after addition of significantly more than four equivalents.