Karlsruhe Institute of Technology, Institut für Physikalische Chemie , Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany.
J Phys Chem A. 2014 Jan 16;118(2):369-79. doi: 10.1021/jp411149e. Epub 2013 Dec 30.
We present structures and photoelectron spectra of Mn(III) and Cu(II) meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) multianions, as well as of homomolecular dimers and trimers thereof. The structural assignments are based on a combination of mass spectrometry, ion mobility measurements, and semiempirical as well as density functional theory (DFT) calculations. Depending on the type of central metal atom, two completely different dimer structural motifs are found. With a central Mn(III), the monomeric units are connected via sulfonic-acid-manganese bonds resulting in a tilted stack arrangement of porphyrin rings. With Cu(II) as the central atom, the sulfonic acid groups preferentially bind to the sodium counterions, resulting in a flat dimer structure with coplanar porphyrins. Photoelectron spectra were recorded for monomers, dimers, and trimers, each in a number of different negative charge states as determined by protonation degree (+nH). In some cases, e.g., Cu(II)TPPS, (Mn(III)TPPS)2 + H, and (Mn(III)TPPS)3 + 3H, we observe electron detachment energies close to zero, or even slightly negative. In all cases, we find a large repulsive Coulomb barrier. The observed trends in detachment energies can be interpreted in terms of a simple electrostatic model.
我们展示了 Mn(III)和 Cu(II) 中四(4-磺酸钠基苯基)卟啉(TPPS)多阴离子的结构和光电子能谱，以及它们的同分子二聚体和三聚体。结构分配是基于质谱、离子迁移率测量以及半经验和密度泛函理论(DFT)计算的结合。根据中心金属原子的类型，发现了两种完全不同的二聚体结构基序。对于中心为 Mn(III)的二聚体，单体单元通过磺酸-锰键连接，导致卟啉环呈倾斜堆叠排列。对于中心为 Cu(II)的二聚体，磺酸基团优先与钠离子抗衡离子结合，导致具有共面卟啉的平面二聚体结构。记录了单体、二聚体和三聚体的光电子能谱，每种都有几个不同的荷电状态(nH)确定的正电荷。在某些情况下，例如Cu(II)TPPS、(Mn(III)TPPS)2 + H和(Mn(III)TPPS)3 + 3H，我们观察到电子离解能接近零，甚至略为负值。在所有情况下，我们都发现了一个很大的排斥库仑势垒。观察到的离解能趋势可以用简单的静电模型来解释。
