The complexes [Et2BL1]4·xylene (1), [Me2AlL1]4 (2), [Et2AlL1]4·toluene (3), [iBu2AlL1]4 (4), [Me2GaL1]4 (5), [Me2AlL2]4 (6), [Et2AlL2]4·toluene (7), [iBu2AlL2]4·toluene (8), and [Me2GaL2]4 (9) (L1=benzimidazolate and L2= 2-methylbenzimidazolate ; E =B, Al, Ga ; R = Me, Et, iBu) were prepared by treatment with L1 or L2 with ER3 in apolar solvents. These compounds have been characterized by spectroscopic methods and single crystal X-ray crystallography for 1-3, 5 and 7-9.
The molecular structures for the complexes with L1 ligand consist of four μ2-dialkylelement moieties bridged in a η1:η1 fashion by L1 forming a 16-membered macrocycle. These compounds show a cavity, which has been estimated assuming a spherical shape. For complexes 1-3 and 5 the radius of the sphere were measured with the more proximal carbon atoms of the two benzimidazole ligands that are coplanar with the macrocycle, giving a volume in the range of 82.4-98.5 Å3.
In the other hand, the molecular structures of complexes 7-9 with L2 ligand adopt a double-cone or 1,3-alternate conformation related to calixarenes. Complexes 7-9 are metallic analogues in which the bridging CH2 moiety of the classical calixarenes are replaced by the fragment MR2. The cavity for 7-9 has been estimated by assuming a truncated cone shape for each of its two components, giving a total volume of ca. 352 Å3 (V =2[(3/π)(h)(a2+ab+b2)]). The complexes 1, 3, 7-9 showed C–H∙∙π interactions of around 3.5 Å with the solvent.