Metal-directed self-assembly of M3L2 (M=Zn, Cd) metal-organic architectures with a tripodal tris-bidentate chelator

Two discrete M3L2 metal-organic architectures, 1 and 2, have been constructed by reaction of a newly designed tripodal tris-bidentate ligand L with M(NO3)(2) (1: M=Zn; 2: M=Cd). Both complexes together with L have been structurally elucidated by single-crystal X-ray crystallography. Complex 1 exhibits a cationic M3L2 coordination architecture bearing three positive charges balanced by three uncoordinated nitrates, while 2 shows a neutral M3L2. 1 and 2 both adopt a compressed trigonal prism shape but show no internal cavity due to close ligand-to-ligand interactions. They display totally different intermolecular packing modes in the solid state, which strongly influence the intermolecular - interactions. Complex 1 has been arrayed such that each M3L2 is surrounded by three neighboring C-3-symmetry related ones, whereas 2 exhibits a columnar molecular stacking. The distinctive intermolecular packing modes in the solid state between 1 and 2 bring about a small but discernible red shift (4nm) corresponding to the - electronic absorption.