Fachbereich Chemie and Forschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
J Chem Phys. 2021 Dec 28;155(24):244305. doi: 10.1063/5.0064966.
Infrared photodissociation (IR-PD) spectra of iron cluster dinitrogen adsorbate complexes [Fe(N)] for n = 8-20 reveal slightly redshifted IR active bands in the region of 2200-2340 cm. These bands mostly relate to stretching vibrations of end-on coordinated N chromophores, a μ end-on binding motif. Density Functional Theory (DFT) modeling and detailed analysis of n = 13 complexes are consistent with an icosahedral Fe core structure. The first adsorbate shell closure at (n,m) = (13,12)-as recognized by the accompanying paper on the kinetics of N uptake by cationic iron clusters-comes with extensive IR-PD band broadening resulting from enhanced couplings among adjacent N adsorbates. DFT modeling predicts spin quenching by N adsorption as evidenced by the shift of the computed spin minima among possible spin states (spin valleys). The IR-PD spectrum of (17,1) surprisingly reveals an absence of any structure but efficient non-resonant fragmentation, which might indicate some weakly bound (roaming) N adsorbate. The multiple and broad bands of (17,m) for all other cases than (17,1) and (17,7) indicate a high degree of variation in N binding motifs and couplings. In contrast, the (17,7) spectrum of six sharp bands suggests pairwise equivalent N adsorbates. The IR-PD spectra of (18,m) reveal additional features in the 2120-2200 cm region, which we associate with a μ side-on motif. Some additional features in the (18,m) spectra at high N loads indicate a μ tilted end-on adsorption motif.
铁核氮吸附配合物[Fe(N)]中 n = 8-20 的红外光解（IR-PD）谱在 2200-2340cm 区域显示出略微红移的 IR 活性带。这些带主要与端接配位 N 发色团的伸缩振动有关，即 μ 端接键合模式。密度泛函理论（DFT）建模和对 n = 13 配合物的详细分析与二十面体 Fe 核结构一致。正如关于阳离子铁团簇对 N 吸收动力学的伴随论文所指出的，第一个吸附物壳层闭合在 (n,m) = (13,12) 处，伴随着相邻 N 吸附物之间增强的耦合导致广泛的 IR-PD 带展宽。DFT 建模预测了 N 吸附引起的自旋猝灭，这表现在计算的自旋能谷中可能的自旋态（自旋谷）之间的自旋最小位置的移动。（17,1）的 IR-PD 光谱令人惊讶地没有显示出任何结构，但却显示出有效的非共振断裂，这可能表明存在一些弱结合（漫游）的 N 吸附物。除了 (17,1) 和 (17,7) 之外，对于所有其他情况的 (17,m)，其多而宽的带表明 N 结合模式和耦合的高度变化。相比之下，（17,7）的六组锐带光谱表明了成对等效的 N 吸附物。（18,m）的 IR-PD 谱在 2120-2200cm 区域揭示了额外的特征，我们将其与 μ 侧接模式相关联。在高 N 负载下，（18,m）谱的一些额外特征表明存在 μ 倾斜的端接吸附模式。
