Mononuclear and Dinuclear Complexes of Isoeilatin

This work describes the synthesis and characterization of mononuclear and dinuclear Ru(II) and Os(II) complexes
based on the symmetrical bridging ligand isoeilatin (1). The crystal structure of 1·[HCl]2 consists of layers of tightly
π-stacked molecules of the biprotonated isoeilatin. The mononuclear complexes [Ru(bpy)2(ieil)]2+ (22+) and [Os(bpy)2(ieil)]2+ (32+) form discrete dimers in solution held together by face-selective π-stacking interactions via the
isoeilatin ligand. Coordination of a second metal fragment does not hinder the π-stacking completely, as demonstrated
by the concentration dependence of the 1H NMR spectra of the dinuclear complexes [{Ru(bpy)2}2{μ-ieil}]4+ (44+),
[{Os(bpy)2}2{μ-ieil}]4+ (54+), and [{Ru(bpy)2}{μ-ieil}{Os(bpy)2}]4+ (64+) and supported by the solid-state structure
of meso-4·[Cl]4. The bridging isoeilatin ligand conserves its planarity even upon coordination of a second metal
fragment, as demonstrated in the solid-state structures of meso-4·[Cl]4, meso-4·[PF6]4, and meso-5·[PF6]4. All of
the dinuclear complexes exhibit a preference (3/2−3/1) for the formation of the heterochiral as opposed to the
homochiral diastereoisomer. Absorption spectra of the mononuclear complexes feature a low-lying dπ(M) → π*(ieil) MLCT band around 600 nm that shifts to beyond 700 nm upon coordination of a second metal fragment.
Cyclic and square-wave voltammetry measurements of the complexes exhibit two isoeilatin-based reduction waves
that are substantially anodically shifted compared to [M(bpy)3]2+ (M = Ru, Os). Luminescence spectra, quantum
yields, and lifetime measurements at room temperature and at 77 K demonstrate that the complexes exhibit 3MLCT
emission that occurs in the IR region between 950 and 1300 nm. Both the electrochemical and photophysical data
are consistent with the low-lying π* orbital of the isoeilatin ligand. The dinuclear complexes exhibit two reversible,
well-resolved, metal-centered oxidation waves, despite the chemical equivalence of the two metal centers, indicating
a significant metal−metal interaction mediated by the bridging isoeilatin ligand.

本研究阐述了基于对称桥联配体异伊拉丁（1）的单一核和二核Ru(II)和Os(II)配合物的合成与表征。异伊拉丁·[HCl]2的晶体结构由紧密π-堆积的双质子化异伊拉丁分子层组成。单一核配合物[Ru(bpy)2(ieil)]2+ (22+)和[Os(bpy)2(ieil)]2+ (32+)在溶液中形成离散的二聚体，这些二聚体通过异伊拉丁配体的面选择性π-堆积相互作用而稳定。第二金属片段的配位并未完全阻碍π-堆积，这由二核配合物[({Ru(bpy)2})2{μ-ieil}]4+ (44+)、[({Os(bpy)2})2{μ-ieil}]4+ (54+)和[({Ru(bpy)2}{μ-ieil}{Os(bpy)2})4+] (64+)的1H NMR谱图的浓度依赖性以及中位-4·[Cl]4的固态结构得到证实。桥联异伊拉丁配体在配位第二金属片段后仍保持其平面性，如中位-4·[Cl]4、中位-4·[PF6]4和中位-5·[PF6]4的固态结构所示。所有二核配合物均表现出对形成杂手性二构体而非同手性二构体的偏好（3/2−3/1）。单一核配合物的吸收光谱显示出在约600 nm的低能级dπ(M) → π*(ieil) MLCT带，该带在配位第二金属片段后移至700 nm以上。该配合物的循环伏安法和方波伏安法测量显示出两个基于异伊拉丁的还原波，这两个波相对于[M(bpy)3]2+ (M = Ru, Os)显著地向阳极偏移。室温及77 K下的发光光谱、量子产率和寿命测量表明，这些配合物在950至1300 nm的近红外区域表现出3MLCT发射。电化学和光物理数据均与异伊拉丁配体的低能级π*轨道一致。尽管两个金属中心在化学上是等价的，但二核配合物表现出两个可逆的、分辨良好的金属中心氧化波，这表明通过桥联异伊拉丁配体介导的显著的金属-金属相互作用。