The synthesis and characterization of a butadiyne linked Rh(III) porphyrin dimer containing a 4,4‘-bipyridine ligand are presented. The crystal structure is compared to the crystal structures of complexes of a monomeric Rh porphyrin with 4,4‘-bipyridine and pyridine, and with the results of molecular modeling.

The X-ray structures of the title complexes revealed that the two zirconium porphyrin moieties are joined either by three bridging hydroxo ligands or by one oxo and two hydroxo ligands. In both structures, the two porphyrin macrocycles are perfectly or nearly eclipsed and concomitantly one of the Zr-O bonds eclipses one of the Zr-N bonds. Such unprecedented eclipsed conformation found in both structures strongly suggests that it is stabilized by dπ-pπ interactions between Zr and O and N atoms despite the unfavorable steric interactions.

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