Ligand Modifications for Tailoring the Binuclear Microenvironments in Schiff-Base Calixpyrrole Pacman Complexes

The synthesis and structures of two new octadentate, Schiff-base calixpyrrole macrocycles are presented in which modifications at the meso-substituents (L-1) or the aryl spacer between the two pyrrole-imine donor compartments (L-2) are introduced. The outcomes of these changes are highlighted in the structures of binuclear Pacman complexes of these macrocycles, [M-2(L-1)] and [M-2(L-2)]. Both palladium and cobalt complexes of the fluorenyl-meso-substituted macrocycle H4L1 adopt rigid, but laterally twisted geometries with enclosed bimetallic microenvironments; a consequence of this spatial constraint is an exo-exo-bonding mode of pyridine in the dicobalt complex [Co-2(py)(2)(L-1)]. In contrast, the use of an anthracenyl backbone between the two donor compartments (H4L2) generates a binuclear palladium complex in which the two PdN4 environments are approximately cofacial and separated by 5.3 angstrom, so generating a bimetallic complex that is structurally very similar to binuclear compounds of cofacial diporphyrins.