Lead(II) and Barium(II) Complexes of a Potentially Octadentate Macrocyclic Ligand (H4L), Capable of Providing Endogenous Alkoxy and Phenoxy Bridges. The X-Ray Crystal Structures of (Pb(H4L)) (ClO4)2, (Pb2(H2L)) (ClO4)2, and ((H6L)(H2O