Sequential Aggregation of Heterometallic {M4X4}‑Cubanes to Wheel-Shaped In10Ni8‑Oxo Clusters for Optical Limiting Application

It is extremely challenging but critical to regulate the structural attributes and physicochemical behaviors of metal-oxo clusters in a controllable manner. Connecting versatile building units and importing aromatic ligands into crystalline materials facilitates the construction of unprecedented structures and provides a platform for the interpretation of structure–activity relationships at the molecular level. In this work, the solvent effect and organic-ligand-induced effect are exploited to formulate and regulate the variety and connection modes of cuboidal {M4X4} building units (M= In, Ni; X= O, Cl) in a controlled and incremental fashion. Not only were the inorganic basic-cubane and its dimeric analogue isolated but also their hexameric aggregation into an In10Ni8-oxo cluster with a wheel-shaped architecture was realized with the assistance of aromatic carboxylates. The In10Ni8-oxo cluster presents the largest size record in the realm of InOCs, and its peripheral surface could be modified to modulate their corresponding physicochemical properties; in particular, the benzoate and naphthoate groups can bring in abundant π···π stacking interactions. Based on the results of Z-scan third-order nonlinear optical (NLO) measurements, these clusters present high reverse saturable absorption (RSA) suitable as optical limiting (OL) materials and constitute an instructive comparison that the general trend of the OL effect is gradually enhanced with the accumulation of more {M4X4}-cubanes including heavy atoms as well as richer and stronger π···π stacking interactions and better delocalization. This work not only starts the research on InOCs-based optical limiting materials but also provide strategies of regulating building units for constructing heterometallic clusters.以可控方式调控金属氧簇（metal-oxo clusters）的结构属性与物理化学行为极具挑战性，却至关重要。将多功能结构基元与芳香配体引入晶体材料，不仅有助于构建前所未有的结构体系，更为在分子水平阐释构效关系提供了理想平台。本研究利用溶剂效应与有机配体诱导效应，以可控且渐进的方式构建并调控立方体型{M₄X₄}结构基元（M为铟In、镍Ni；X为氧O、氯Cl）的种类与连接模式。研究中不仅分离得到了无机基立方烷及其二聚体类似物，还借助芳香羧酸盐配体，成功实现了这类基元的六聚体聚集，得到具有轮状结构的In₁₀Ni₈氧簇。该In₁₀Ni₈氧簇是目前铟氧簇（Indium-Oxo Clusters, InOCs）领域中尺寸最大的体系，其外围表面可通过修饰调控相关物理化学性质；其中苯甲酸根与萘甲酸根基团可引入丰富的π···π堆积相互作用。通过Z扫描三阶非线性光学（third-order nonlinear optical, NLO）测试表征发现，这类簇合物表现出优异的反饱和吸收（reverse saturable absorption, RSA）性能，可作为光限幅（optical limiting, OL）材料使用；进一步对比分析可知，随着体系中含重原子的{M₄X₄}立方烷结构基元数量增加、π···π堆积相互作用更丰富且更强、电子离域性更优异，光限幅效应的整体强度也随之逐步提升。本研究不仅开启了基于铟氧簇的光限幅材料研究方向，同时为构建异金属簇合物提供了调控结构基元的可行策略。