title: Effect of chelate ring expansion on Jahn-Teller distortion and Jahn-Teller dynamics in copper(II) complexes.
abstract: The expanded ligand N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridin-2,6-diamine (ddpd) coordinates to copper(II) ions in a meridional fashion giving the dicationic complex mer-[Cu(ddpd)(2)](BF(4))(2) (1). In the solid state at temperatures below 100 K the cations of 1 localize in Jahn-Teller elongated CuN(6) polyhedra with the longest Cu-N bond pointing in the molecular x or y directions while the z axis is constrained by the tridentate ddpd ligand. The elongated polyhedra are ordered in an antiferrodistortive way giving an idealized zincblende structure. At higher temperature dynamically averaged (fluxional) polyhedra in the molecular x/y directions are observed by multifrequency variable temperature electron paramagnetic resonance (EPR) and by variable temperature X-ray diffraction studies. Compared to [Cu(tpy)(2)](2+) (tpy = 2,2';6',2″-terpyridine) the Jahn-Teller splitting 4δ(1) of 1 is larger. This is very probably caused by the much more favorable orbital overlap in the Cu-N bonds in 1 which results from the larger bite angle of ddpd as compared to tpy. The "freezing-in" of the Jahn-Teller dynamics of 1 (T ≈ 100 K) occurs at higher temperature than observed for [Cu(tpy)(2)](2+) (T < 77 K) which is also probably due to the larger Jahn-Teller distortion of 1 resulting in a larger activation barrier.
authors: Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-University of Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
authors: Katharina
authors: K
authors: Mack
authors: Anica
authors: A
authors: Wünsche von Leupoldt
authors: Christoph
authors: C
authors: Förster
authors: Maria
authors: M
authors: Ezhevskaya
authors: Dariush
authors: D
authors: Hinderberger
authors: Karl W
authors: KW
authors: Klinkhammer
authors: Katja
authors: K
authors: Heinze