Large M4L4 (M = Al(III), Ga(III), In(III), Ti(IV)) tetrahedral coordination cages: an extension of symmetry-based design

As an extension to a rational design for the formation of self-assembled coordination cages, the syntheses for very large M4L4 tetrahedra based on a hexadentate 3-fold symmetric ligand (1,3,5-tris(4'-(2' ',3' '-dihydroxybenzamido)phenyl)benzene (H6L2)) are described. Four tetrahedral M4L2(4) assemblies (M = Al(III), Ga(III), In(III), Ti(IV)), with cavity sizes of around 450 A3, have been characterized by elemental analysis, NMR spectroscopy, and high-resolution electrospray mass spectrometry. Differences in chiral resolution and dynamic behavior of host-guest interactions with previously reported tetrahedral M4L(N)6 and M4L1(4) architectures are highlighted for the ligands 1,5-bis(2',3'-dihydroxybenzamido)naphthalene (H4L(N)) and 1,3,5-tris(2',3'-dihydroxybenzamido)benzene (H6L1). An even larger 3-fold symmetric ligand, 1,3,5-tris(4'-(2' ',3' '-dihydroxybenzamido)-1',1' '-biphenyl)benzene (H6L3) has been prepared but, due to increased flexibility and deviation from the intended 3-fold symmetry, does not undergo self-assembly to form the M4L3(4) structure.