ZIRCONIUM(IV) SANDWICH COMPLEXES OF PORPHYRINS AND TETRAAZAPORPHYRINS- SYNTHESIS, STRUCTURE, AND NONLINEAR-OPTICAL PROPERTIES

A family of bis(porphyrin) zirconium sandwich complexes containing oct aethylporphyrin (OEP) and octaethyltetraazaporphyrin (OETAP) was synth esized and characterized by W-vis and NMR spectroscopies. The two liga nds are structural analogues yet have dramatically different redox pro perties (the redox potentials of OETAP complexes are much more positiv e than those of the corresponding OEP complexes). Cyclic voltammetry r esults indicate that Zr(OETAP)(2) is about 600 mV harder to oxidize an d about 600 mV easier to reduce than Zr(OEP)2, while the mixed sandwic h Zr(OEP)(OETAP) exhibits intermediate redox potentials. The structure s of Zr(OEP)(OETAP) and Zr(OETAP)2 were determined by X-ray crystallog raphy and compared to Zr(OEP)(2). The solid state structures were very similar, indicating that OEP and OETAP have similar steric parameters and that observed spectroscopic and electrochemical differences are d ue primarily to electronic factors. The one electron oxidized porphyri n sandwiches were also synthesized. Characterization by W-vis, near-IR , EPR, and IR spectroscopies confirm the it radical nature of these co mplexes. IR spectra indicate that the cation is delocalized over the e ntire complex in both [Zr(OEP)(OETAP)](+)[SbCl6](-) and [Zr(OETAP)(2)] (+)[SbCl6](-), consistent with a strongly coupled pi system. Additiona l evidence for strong coupling was obtained from measurement of the no nlinear optical properties of the mixed complex; the molecular hyperpo larizability is negative, indicating that the dipole moment reverses d irection upon electronic excitation.