Lawson Daku Latévi M
Département de Chimie Physique, Université de Genève Quai E. Ansermet 30 CH-1211 Genève 4 Switzerland
RSC Adv. 2020 Dec 7;10(71):43343-43357. doi: 10.1039/d0ra09499d. eCollection 2020 Nov 27.
In order to achieve an in-depth understanding of the role played by the solvent in the photoinduced low-spin (LS) → high-spin (HS) transition in solvated Fe(ii) complexes, an accurate description of the solvated complexes in the two spin states is required. To this end, we are applying state-of-the-art molecular dynamics (AIMD) simulations to the study of the structural and vibrational properties of iron(ii) polypyridyl complexes. Two aqueous LS complexes were investigated in this framework, namely, [Fe(bpy)] (bpy = 2,2'-bipyridine) [Lawson Daku and Hauser, , 2010, , 1830; Lawson Daku, , 2018, , 6236] and [Fe(tpy)] (tpy = 2,2':6',2''-ter-pyridine) [Lawson Daku, , 2019, , 650]. For aqueous [Fe(bpy)], combining the results of forefront wide-angle X-ray scattering experiments with those of the AIMD simulations allowed the visualization of the interlaced coordination and solvation spheres of the photoinduced HS state [Khakhulin , , 2019, , 9277]. In this paper, we report the extension of our AIMD studies to the spin-crossover complex [Fe(tpen)] (tpen = ,,','-tetrakis(2-pyridylmethyl)ethylenediamine) in acetonitrile (ACN). The determined LS and HS solution structures of the complex are in excellent agreement with the experimental results obtained by high-resolution transient X-ray absorption spectroscopy [Zhang , , 2019, , 6375]. The first solvation shell of [Fe(tpen)] consists of ACN molecules located in the grooves defined by the chelating coordination motif of the tpen ligand. Upon the LS → HS change of states, the solvation number of the complex is found to increase from ≈9.2 to ≈11.9 and an inner solvation shell is formed. This inner solvation shell originates from the occupancy by about one ACN molecule of the internal cavity which results from the arrangement of the 4 pyridine rings of the tpen ligand, and which becomes accessible to the solvent molecules in the HS state only thanks to the structural changes undergone by the complex. The presence of this inner solvation shell for the solvated HS complex probably plays a key role in the spin-state dependent reactivity of [Fe(tpen)] in liquid solutions.
为了深入了解溶剂在溶剂化铁（II）配合物的光致低自旋（LS）→高自旋（HS）转变中所起的作用，需要对两种自旋态下的溶剂化配合物进行准确描述。为此，我们正在应用最先进的分子动力学（AIMD）模拟来研究铁（II）多吡啶配合物的结构和振动性质。在此框架下研究了两种水相LS配合物，即[Fe(bpy)]（bpy = 2,2'-联吡啶）[劳森·达库和豪泽，2010年，1830；劳森·达库，2018年，6236]和[Fe(tpy)]（tpy = 2,2':6',2''-三联吡啶）[劳森·达库，2019年，650]。对于水相[Fe(bpy)]，将前沿广角X射线散射实验结果与AIMD模拟结果相结合，得以可视化光致HS态的交错配位和溶剂化球层[哈胡林，2019年，9277]。在本文中，我们报告了将AIMD研究扩展至乙腈（ACN）中的自旋交叉配合物[Fe(tpen)]（tpen = N,N,N',N'-四（2-吡啶甲基）乙二胺）。该配合物确定的LS和HS溶液结构与通过高分辨率瞬态X射线吸收光谱法获得的实验结果[张，2019年，6375]高度吻合。[Fe(tpen)]的第一溶剂化层由位于tpen配体螯合配位基序所定义凹槽中的ACN分子组成。随着状态从LS变为HS，发现该配合物的溶剂化数从约9.2增加到约11.9，并形成了一个内部溶剂化层。这个内部溶剂化层源于tpen配体的4个吡啶环排列所形成的内部空腔被约一个ACN分子占据，并且只有由于配合物发生的结构变化，该空腔在HS态下才对溶剂分子可及。溶剂化HS配合物中这种内部溶剂化层的存在可能在[Fe(tpen)]在液体溶液中自旋态依赖性反应性中起关键作用。
