X-ray Structures of a Phenanthroline-Strapped Porphyrin and Its Dihydrated Zinc(II) Complex: Convergent Distal Hydrogen Bonds and "CH···O" Interactions

The X-ray structure of a phenanthroline-(phen-)strapped 1,10-diphenylporphyrin 1 has been resolved. From the structure obtained, it is apparent that in spite of the rigidity of the strap the porphyrin ring is only slightly distorted, and that the substituents on the phen moiety define what would seem to be a hydrophobic pocket. Metallation of the free base 1 with zinc (II) acetate yields a metallic complex (1)Zn with a free axial coordination site. Crystallization of the zinc complex in the presence of a hindered base (N-methylimidazole, denoted N-MeIm) in organic solvents affords single crystals of a porphyrinatozinc(II) species, in which two water molecules are surprisingly present in the encumbered (distal) pocket of the phen site. One water molecule is axially bound to the zinc(II) ion, while the other is doubly hydrogen-bonded, as an H-bond donor to the phenanthroline and as an H-bond acceptor to the axial water ligand.