Department of Chemistry , UiT-The Arctic University of Norway , Tromsø N-9037 , Norway.
Advanced Light Source , Lawrence Berkeley National Laboratory , Berkeley , California 94720-8229 , United States.
Inorg Chem. 2018 Aug 20;57(16):9656-9669. doi: 10.1021/acs.inorgchem.8b00537. Epub 2018 Jun 6.
Presented herein is a detailed multitechnique investigation of ligand noninnocence in S = / manganese corrole derivatives at the formal Mn oxidation state. The Soret maxima of Mn[T pXPC]Cl (T pXPC = meso-tris( p-X-phenyl)corrole, where X = CF, H, Me, and OMe) were found to red-shift over a range of 37 nm with increasing electron-donating character of X. For Mn[T pXPC]Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole-like ligand for the MnCl complexes and an innocent corrole ligand for the MnPh complexes. Single-crystal X-ray structures of three Mn[T pXPC]Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn[T pOMePC]Ph. B3LYP density functional theory (DFT) calculations on Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities, consistent with an antiferromagnetically coupled Mn-corrole description. By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an essentially Mn-corrole description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of 0.6 eV for the Mn K-pre-edge of Mn[T pCFPC]Ph and a striking enhancement of the pre-edge intensity, relative to Mn[T pCFPC]Cl, consistent with a more oxidized, i.e., Mn, center in Mn[T pCFPC]Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn[T pCFPC]Ph results from the extra 3d hole, which mixes strongly with the Mn 4p orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. Cyclic voltammetry measurements revealed highly negative first reduction potentials for the Mn[T pXPC]Ph series (∼-0.95 V) as well as large electrochemical HOMO-LUMO gaps of ∼1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the Mn-Ph bond.
本文详细研究了在形式 Mn 氧化态下 S=/锰卟啉衍生物中配体的非中性。发现 Mn[T pXPC]Cl（T pXPC=meso-三（p-X-苯基）卟啉，其中 X=CF、H、Me 和 OMe）的 Soret 最大值随着 X 的供电子特性的增加而红移了 37nm。相比之下，对于 Mn[T pXPC]Ph，复合物的 Soret 包络在很大程度上与 X 无关。这些观察结果表明，MnCl 配合物中的配体是非中性卟啉样的，而 MnPh 配合物中的配体是中性卟啉样的。三个 Mn[T pXPC]Cl 配合物的单晶 X 射线结构显示出骨架键长交替，表明存在非中性卟啉，而 Mn[T pOMePC]Ph 则没有观察到这种交替。对 Mn[TPC]Cl 的 B3LYP 密度泛函理论（DFT）计算得出，α和β自旋密度有很强的空间分离，与反铁磁耦合的 Mn-卟啉描述一致。相比之下，对于 Mn[TPC]Ph，发现α和β自旋密度的空间分离相对较小，与基本的 Mn-卟啉描述一致。近边 X 射线吸收光谱（XANES）显示，Mn[T pCFPC]Ph 的 Mn K 边预边带蓝移了 0.6eV，且相对于 Mn[T pCFPC]Cl，预边强度显著增强，这与 Mn[T pCFPC]Ph 中更氧化的 Mn 中心一致。时间依赖的 DFT 计算表明，Mn[T pCFPC]Ph 的 Mn K 边预边强度的增强是由于额外的 3d 空穴，它与 Mn 4p 轨道强烈混合。结合对 Fe[TPC]Cl 和 Fe[TPC]Ph 的类似结果，本研究强调了金属 K 边 XANES 在探测第一过渡金属卟啉中的配体非中性方面的巨大潜力。循环伏安测量显示 Mn[T pXPC]Ph 系列的第一个还原势非常负（约-0.95V），并且 HOMO-LUMO 能隙约为 1.7V。然而，第一个还原是不可逆的，这表明 Mn-Ph 键的断裂。
