Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-University of Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
Inorg Chem. 2012 Jul 16;51(14):7851-8. doi: 10.1021/ic300929g. Epub 2012 Jul 2.
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)(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) (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) (T < 77 K) which is also probably due to the larger Jahn-Teller distortion of 1 resulting in a larger activation barrier.
扩展配体 N,N'-二甲基-N,N'-二吡啶-2-基-吡啶-2,6-二胺（ddpd）以顺式方式与铜（II）离子配位，形成阳离子配合物 mer-Cu(ddpd)(2)(2)（1）。在低于 100 K 的温度下，1 的阳离子在 Jahn-Teller 拉长的 CuN(6)多面体中局部化，最长的 Cu-N 键指向分子的 x 或 y 方向，而 z 轴受到三齿 ddpd 配体的约束。拉长的多面体以反铁磁扭曲的方式有序排列，形成理想的闪锌矿结构。在较高温度下，通过多频变温电子顺磁共振（EPR）和变温 X 射线衍射研究观察到分子 x/y 方向上动态平均（通量）多面体。与 Cu(tpy)(2)（tpy = 2,2';6',2″-三联吡啶）相比，1 的 Jahn-Teller 分裂 4δ(1)更大。这很可能是由于 1 中 Cu-N 键的轨道重叠更有利，这是由于 ddpd 的咬合角度比 tpy 大。1 的 Jahn-Teller 动力学的“冻结”（T ≈ 100 K）发生在比观察到的 Cu(tpy)(2)（T < 77 K）更高的温度下，这也可能是由于 1 的 Jahn-Teller 变形更大，导致活化能垒更大。
