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.