Gallium(III) and indium(III) octaethylporphyrin dimeric complexes with a single μ-hydroxo bridge: synthesis, structure and stability in anion-containing organic media

Abstract

The synthesis and single-crystal X-ray structures of the hydroxo-bridged complexes (μ-hydroxo)-bis(octaethylporphinato)gallium(III)perchlorate {[Ga(OEP)] 2OH}ClO 4 and (μ-hydroxo)-bis(octaethylporphinato)indium(III)tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate {[In(OEP)] 2OH}TFPB are reported. These complexes are prepared by the titration of monomeric metalloporphyrin species in dichloromethane with diluted perchloric acid or by the addition of stoichiometric amounts of the tetraphenylborate derivative salt. The structures show that complexes of two metalloporphyrins are joined by a single protonated metaloxygenmetal bridge with a nearly 150° bridge angle. The porphyrin rings of the dimers form dihedral angles of 15° Ga(III) and 23° In(III). In contrast to previously reported analogous dimeric Mn(III) and Fe(III) structures, the porphyrin rings of the present dimers are twisted by a much greater torsion angle of nearly 22°. In dichloromethane, high stability of the dimers is observed in the presence of perchlorate, but dissociation of the dimer species to monomers is found with increasing concentrations of halogen anions. This corresponds well with the observed anion selectivities recently reported for both electrochemical and optical anion sensors prepared with the respective Ga(III) and In(III) octaethylporphyrins in polymeric films.