Munshi Musleh Uddin, Martens Jonathan, Berden Giel, Oomens Jos
Radboud University , Institute for Molecules and Materials, FELIX Laboratory , Toernooiveld 7 , 6525 ED Nijmegen , The Netherlands.
University of Amsterdam , Science Park 904 , 1098 XH Amsterdam , The Netherlands.
J Phys Chem A. 2019 May 16;123(19):4149-4157. doi: 10.1021/acs.jpca.9b00793. Epub 2019 May 7.
We report the fingerprint IR spectra of mass-isolated gaseous coordination complexes of 2,2'-bipyridine (bpy) and 1,4,8,11-tetra-azacyclotetradecane (cyclam) with a copper ion in its I and II oxidation states. Experiments are carried out in a quadrupole ion trap (QIT) mass spectrometer coupled to the FELIX infrared free-electron laser. Dications are prepared using electrospray ionization (ESI), while monocations are generated by charge reduction of the dication using electron transfer-reduction (ETR) in the QIT. Interestingly, [Cu(bpy)] can also be generated directly using ESI, so that its geometries as produced from ETR and ESI can be compared. The effects of charge reduction on the IR spectra are investigated by comparing the experimental spectra with the IR spectra modeled by density functional theory. Reduction of Cu(II) to the closed-shell Cu(I) ion retains the square-planar geometry of the Cu-cyclam complex. In contrast, for the bis-bpy complex with Cu, charge reduction induces a conversion from a near-square-planar to a tetrahedral geometry. The geometry of [Cu(bpy)] is identical to that of the complex generated directly from ESI as a native structure, which indicates that the ETR product ion thermalizes. For [Cu(cyclam)], however, the square-planar geometry of the 2+ complex is retained upon charge reduction, although a (distorted) tetrahedral geometry was predicted to be lower in energy. These differences are attributed to different barriers to rearrangement.
我们报道了处于I和II氧化态的铜离子与2,2'-联吡啶（bpy）和1,4,8,11-四氮杂环十四烷（环胺）形成的质量分离气态配位络合物的指纹红外光谱。实验在与FELIX红外自由电子激光耦合的四极杆离子阱（QIT）质谱仪中进行。使用电喷雾电离（ESI）制备双阳离子，而单阳离子则通过在QIT中使用电子转移还原（ETR）对双阳离子进行电荷还原产生。有趣的是，[Cu(bpy)]也可以直接使用ESI生成，从而可以比较由ETR和ESI产生的其几何结构。通过将实验光谱与密度泛函理论模拟的红外光谱进行比较，研究了电荷还原对红外光谱的影响。将Cu(II)还原为闭壳层Cu(I)离子保留了Cu-环胺络合物的平面正方形几何结构。相比之下，对于含铜的双bpy络合物，电荷还原会导致从近平面正方形几何结构转变为四面体几何结构。[Cu(bpy)]的几何结构与作为天然结构直接由ESI生成的络合物相同，这表明ETR产物离子发生了热弛豫。然而，对于[Cu(环胺)]，尽管预测（扭曲的）四面体几何结构能量较低，但在电荷还原后2+络合物的平面正方形几何结构得以保留。这些差异归因于重排的不同势垒。
