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Further symmetrical cerium(1V) bisporphyrinates are prepared from cerium(II1) acetylacetonate and tetraphenylporphyrin, tetra-p-chlorophenylporphyrin, and hexadecahydrotetrabenzporphyrin. In the latter case, a biscerium(II1) tripledecker is also found which is the only product in the case of octamethylporphyrin. From a mixture of two different porphyrins, namely octaethylporphyrin [H,(OEP)] and either tetraphenylporphyrin [HATPP)] or tetra-pchlorophenylporphyrin m,(TClP)], besides the symmetrical species Ce(OEP)2 and Ce(TPPk, the unsymmetrical ("mixed") double-deckers Ce(OEP)(TPP) or Ce(OEPXTC1P) are obtained which have different porphyrin rings in the sandwich system and can be separated by chromatography. The crystal structure analysis of Ce(OEP)(TPP) shows Ce" in a square-antiprismatic geometry of the pyrrole N atoms of the porphyrin rings. While the IR and NMR spectra of the unsymmetrical double-deckers are superpositions of the spectra of the individual rings, their W/vrS spectra and cyclic voltammograms indicate that the two porphyrin rings behave as a common n-electron system. The preparation of the x-cation radical salts [Ce(OEP)23C104 and [Ce(OEP)(TPP)]SbCI, is also described. In the latter, the defect electron seems to reside preferentially in the OEP ring.While sandwich-like metal(1V) bis(tetrapyrro1es) with square-antiprismatic geometry are known for a long time in the phthalocyanine series, e. g. Sn(Pc);' or Th(Pc):' , papers on the preparation of CeIV5' or Th" and U1' bisporphyrinates6' have not appeared before 1983 when the synthesis of the cerium(1V) bis(tetra-p-tolylporphyrinate) double-decker, Ce(TTP)2 (1 B, see Scheme I), was described ' I. Since these sandwich systems can be regarded as structural and spectroscopic models 5d-f~6b) of the special pair of bacteriochlorophyll molecules in the reaction centre of bacterial photosynthesis'), the photophysical properties9' and resonance Raman spectra"' have been measured; these studies were also promoted by the idea that these sandwich systems might serve as molecular metals"' or intrinsic semiconductors"' when one of the rings is oxidized to a radical as, e. g., in Lu(Pc)~'? Therefore, a somewhat broader variation of these molecules seems appropriate. These variations may include incorporation of two different kinds of tetrapyrrole ligands as was achieved for the first time with the tripledecker Nd2(Pc)2(TAP)'". Likewise, the mixed system Ce(OEP)(TTP)

In der Tat gelingt die Oxidation priiparativ durch Umsetzung der Ce'"-Doppeldecker Ce(TTP)2 rnit dem Hexachloroantimonat des Phenoxathiin-Radikalkation~~'] in 1,2-Dichlorethan (DCE) gemllj Gleichung (c):

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Q VCH Verlagsgeseiischaji mbH, 0-6940 Weinheim, 1986 0570-0833/86/0303-0287 $ OZ.ZO/O