Département de chimie moléculaire

Reacting the fluorous carboxylate C8F17CO2·HNEt3 with Cu(OTf)2 in acetone leads, depending on the carboxylate/Cu ratio, either to the neutral dimeric complex [Cu2(C8F17CO2)4(acetone)2] (2), or to the dianionic monomeric complex [Cu(C8F17CO2)4](HNEt3)2 (4). Both complexes were characterized by IR, UV-visible and EPR spectroscopies, magnetic susceptibility measurements and x-ray diffraction anal. 2 Displays the classical dimeric paddlewheel structure with four carboxylates bridging the two Cu(II) ions while 4 displays an unusual monomeric structure with four monodentate carboxylates bounded to the Cu(II) in a square planar geometry. In contrast to 4, the complex 2 shows a very high affinity for H2O vapors in the solid state and behaves as a magnetic sponge. When exposed to air, ground crystals of 2 rapidly trap up to 6 H2O mols. per Cu ion decreasing the magnetic coupling from 2J = -480 cm-1 to 2J = -7 cm-1. The hydration process is accompanied by drastic changes of the EPR and FTIR spectra, revealing that the binding of the H2O mols. to the Cu atoms leads to the release of the acetone ligands from the solid and to the shifting of two carboxylates from bridging bidentate to nonbridging monodentate coordination mode. When hydrated 2 is exposed to high vacuum, the H2O mols. are removed from the solid. The dehydration process leads to the partial recovery of the antiferromagnetic coupling between the Cu(II) ions as revealed by EPR and magnetic susceptibility measurements. The hydration/dehydration process is not accompanied by a fully reversible structural rearrangement in the solid state. The unusual affinity for H2O and consequently, the modification of the magnetic properties, is obsd. neither with the fluorous dimeric complex 1, nor with the dianionic monomeric complex 4. [on SciFinder(R)]