Ferromagnetic versus Antiferromagnetic Exchange Interactions in Tetrathiafulvalene-Based 3d/4f Heterobimetallic Complexes

(TTF-salphen)M compounds (TTF-salphen(2-) = 4,5-bis(propylthio)tetrathiafulvalene-N,N'-phenylenebis(salicylideneimine) dianion; M = Cu-II and Ni-II) have been treated with Ln(hfac)(3)center dot 2H(2)O precursors (hfac(-) = 1,1,1,5,5,5-hexafluoroacetylacetonate anion; Ln = Gd-III, Tb-III, and Dy-III) to elaborate unprecedented 3d/4f TTF-based heterobimetallic complexes of formula [(TTF-salphen)MLn(hfac)(3)]. All the structures of these compounds have been resolved by X-ray diffraction on single crystals. The structures of these complexes are formed by a TTF-salphen(2-) ligand coordinated to the 3d metal ions in the inert tetradentate N2O2 site. The Ln(hfac)(3) fragment is coordinated to the (TTF-salphen)M one through the two phenolate bridges. Even if the complexes are similar in both Cu-II and Ni-II families, the crystal packing is different. In the first case, dimers of TTF-salphen(2-) donors constitute the organic network. In the other case, a reminiscent organic network is observed with S center dot center dot center dot S contacts. The photophysical properties of [(TTF-salphen)CuDy(hfac)(3)] (3) in chloroform solution highlight the redshift of the TTF -> salphen charge transfer (400 cm(-1)) relative to the analogue excitations in (TTF-salphen) Cu, which attest to the stability of these structures in solution. Static magnetic measurements have allowed us to quantify the ferromagnetic interactions (J=+1.29 cm(-1)) between Cu-II and Gd-III in the [(TTF-salphen)CuGd(hfac)(3)] complex. Finally, an empirical method that consists of the comparisons of the magnetic properties of [(TTF-salphen)CuTb(hfac)(3)] with [(TTF-salphen)NiTb(hfac)(3)] and [(TTF-salphen)CuDy(hfac)(3)] with [(TTF-salphen)NiDy(hfac)(3)] has established that ferromagnetic interactions take place between Cu-II and Tb-III ions, whereas unusual antiferromagnetic interactions have been identified between Cu-II and Dy-III ions.