The self-assembly of a [Ga4L6](12-) tetrahedral cluster thermodynamically driven by host-guest interactions

The guest-induced synthesis of a [Ga4L6](12-) tetrahedral metal-ligand cluster resulting from a predictive design strategy is described. Each of the six dicatecholamide ligands spans an edge of the molecular tetrahedron with four Ga(III) ions at the vertices. Small cationic species not only were found to occupy the large void volume (ca. 300-400 A(3)) inside this cluster but also are necessary thermodynamically to drive cluster assembly via formation of a host-guest complex. NMe4(+), NEt4(+), and NPr4(+) all suit this purpose, and in addition the cluster exhibits a preference in the binding of these three guests: NEt4(+) is bound 300 times more strongly than NPr4(+), which is in turn bound 4 times more strongly than NMe4(+), as determined by 1H NMR spectroscopy. The K6(NEt4)6[Ga4L6] cluster was characterized by NMR spectroscopy, high- (Fourier transform ion cyclotron resonance, FT-ICR) and low-resolution electrospray ionization (ESI) mass spectrometry, elemental analysis, and single-crystal X-ray diffraction. The binding of the NEt4(+) guest molecule was confirmed in the solid state structure, which reveals that the molecule contains large channels in the solid state. As this result exemplifies, it is suggested that guest molecules will play an increasing role in the formation of larger, predesigned metal-ligand clusters.