Preparation and Properties of Gadolinium Homoleptic Double- and Triple-Decker Complexes Containing Tetrabenzoporphyrin Ligand

Two novel gadolinium sandwich-type complexes containing tetrabenzoporphyrin (TBP) ligands- Gd(TBP)(2) and Gd(TBP)(3) were prepared from porphyrin 1 and Gd(acac)(3)center dot nH(2)O under Ar by boiling 1, 2, 4-Tcb for 15 similar to 17h and 45 similar to 48 h respectively. Their structures are characterized by Uv-Vis, HR-MS and IR. The spectroscopic studies show that their longest-wavelength visible and near-IR absorption bands are obviously red-shifted due to the extension of the pi conjugated systems in the TBP ring. The magnetic studies indicate that the observed value of chi T-M for Gd(TBP)(2) is close to the combined value of Gd(III) and porphyrin radical anion at room temperature and that antiferromagnetic interaction possibly results from the intramolecular spin exchange between the porphyrin it-radical electron and that the gadolinium f unpaired electrons dominates its magnetic properties over the whole temperature range while there is no magnetic interactions between two Gd(III) ions in Gd(TBP)(3) in the range from room temperature down to 20K and very weak antiferromagnetic coupling exsits between two Gd(III) ions below 20K. Since Buchler and co-workers first reported bis (porphyrinato) metal complexes M(Por)(2) such as a cerium(IV) bisporphyrinate, Ce(TPP)(2) in 1983([1]), sandwich-type rare earth complexes containing porphyrin ligands have been the subject of intensive studies because of the unusual physical, spectroscopic, redox, electron transfer, and/or conductivity properties resulting from their strong pi-pi interactions([2-3]). Whereas the chemistry and properties of homoleptic sandwich complexes with the same pophyrinato ligands of various lanthanide, actinides and group 4 transition metals have been extensively studied([4]), and the heteroleptic analogus containing mixed macrocyclic ligands have also been described([5-6]) for an intensive investigation of the pi-pi interactions, actually all of them are confined to the sandwich-type complexes containing meso-substituted porphyrin ligands except for octaethylporphyrin (OEP) or octamethylporphyrin (OMP). Little is known about sandwich-like complexes with aromatic ring-fused porphyrin ligands that contain a more delocalized it system. In this paper, we will describe the preparation, spectroscopic characterization and magnetic properties of two novel gadolinium homoleptic double- and triple-decker sandwich-type complexes with tetrabenzoporphyrin (TBP) ligand (Fig.1)