Self-Assembled M2L4 Nanocapsules: Synthesis, Structure and Host-Guest Recognition Toward Square Planar Metal Complexes †

Metallosupramolecular cages of the general formulas [M₂(L)₄][X]₄ can be self-assembled in good yields, where M = Pd, X = NO₃, L = L¹ (1a); M = Pd, X = OTf, L = L¹ (1b); M = Pt, X = OTf, L = L¹ (2); M = Pd, X = OTf, L = L² (3); L¹ = 1,3-bis(pyridin-3-ylethynyl)-5-methoxybenzene; and L² = 2,6-(pyridin-3-ylethynyl)- 4-methoxyaniline, respectively. These cages have been fully characterized using ¹H, 13C NMR, elemental analysis, IR spectroscopy, and electrospray mass spectrometry. Additionally the molecular structure of [Pd₂(L¹)₄][OTf]₄ (1b) was confirmed using single crystal X-ray diffraction. The capacity of central cavities of M₂L₄ cages to accommodate square planar metal complexes was investigated. In particular, the tetracationic cage [Pd₂(L²)₄][OTf]₄ (3) was found to encapsulate the anionic metal complex [PtCl₄]2- through electrostatic interactions and also via hydrogen bonding with the amino groups of the bridging ligand displayed by this nanocage.