Département de chimie moléculaire

The syntheses and single-crystal x-ray structures of mononuclear [Cu(bmet)](ClO4)2·H2O, [Cu(bmet)]Br2·2MeCN, and [Zn(bmet)](ClO4)2·H2O ( bmet = N,N'-bis(2,2'-bipyridin-6-ylmethyl)ethane-1,2-diamine) are described. All three complexes feature a central metal ion bound to all six N atoms of the bmet ligand, which displays a meridional-facial-facial-meridional (mffm) configuration. The three complexes show one N-M-N axis to be significantly shorter than the others in agreement with an apparent compressed octahedral geometry. The x-ray structures of a single crystal of [Cu(bmet)](ClO4)2·0.375H2O resolved from data recorded at different temps. display no remarkable structural modifications. However, they all display both as a powder and, in soln., an axial g1 {\textgreater} g2 ⪆ g3 {\textgreater} ge EPR pattern at low temp., which is indicative of tetragonally elongated octahedra, while at room temp. the Q-band EPR spectra display a more rhombic g1 ⪆ g2 {\textgreater} g3 {\textgreater} ge pattern. The fully d. functional theory optimized structure of the CuII complexes displays significant structural modifications only along one Nimine-M-Namine axis resulting in an elongated octahedral structure. Also, the EPR parameters predicted from this structure are comparable to those detd. exptl. from the axial EPR signal recorded at low temp., consistent with the unpaired electron residing mainly in the {\{}3dx2-y2{\}} orbital. The structural and electronic properties of [Cu(bmet)]2+ are different from those in other previously described dynamic Jahn-Teller systems. Probably these data can should be rationalized by a dynamic Jahn-Teller effect perturbed by the strain of the hexadentate bmet ligand. [on SciFinder(R)]