Synthesis and physicochemical characterization of protonated and deprotonated forms in heteroleptic lanthanide(III) porphyrinate double-deckers. X-ray structure of (GdH)-H-III(oep)(tpp) at 298 and 21 K

The synthesis, spectroscopic characterization, and electrochemical study of eleven heteroleptic and their corresponding homoleptic lanthanide sandwich es are reported. Studies in solution have been carried out in solvents of d ifferent basicity, in order to elucidate the equilibrium between the proton ated and deprotonated form of these complexes. The investigated compounds a re represented by the formulas Ln(III)H(oep)(tpp) and [Ln(III)(oep)(tpp)](- ) corresponding to the protonated and deprotonated forms, respectively (in the case of heteroleptic), and the formulas Ln(III)H(tpp)(2) and [Ln(III)(t pp)(2)](-) (in the case of the homoleptic porphyrin double-deckers), where Ln Nd, ..., Lu (except Pm), oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate , and tpp = 5,10,15,20-tetraphenylporphyrinate). Various spectroscopic meth ods are used for the physicochemical characterization of the title complexe s. The electronic spectra of the complexes above present different features in CH2Cl2 and in DMF. In the latter solvent they reveal features similar t o those of the analogous actinide(IV) porphyrin double-decker. The electroc hemical studies carried out in CH2Cl2 and THF demonstrate clearly that the redox behavior of the double-deckers, heteroleptic or homoleptic, is strong ly dependent on the proton on the porphyrinic core. In CH2Cl2, four reversi ble oxidation processes and two quasi-reversible waves are observed for the protonated species in both homo- and heteroleptic double-deckers. In contr ast, two oxidations and two reductions are observed in THF for the homolept ic derivatives, while the corresponding heteroleptic ones undergo three oxi dations and one reduction process. The structure of the new heteroleptic do uble-decker (GdH)-H-III(oep)(tpp) was determined by X-ray diffraction at 29 8 and 21 K. Both structures are compared with the first analogous structure of (SmH)-H-III(oep)(tpp). According to the spectroscopic and structural da ta reported for the heteroleptic protonated derivatives, the oep macrocycle is the favored binding site of the proton in solutions as well as in the s olid state.