Atomically accurate site-specific ligand tailoring of highly acid- and alkali-resistant Ti(iv)-based metallamacrocycle for enhanced CO 2 photoreduction.

Skillfully engineering surface ligands at specific sites within robust clusters presents both a formidable challenge and a captivating opportunity. Herein we unveil an unprecedented titanium-oxo cluster: a calix[8]arene-stabilized metallamacrocycle (Ti 16 L 4 ), uniquely crafted through the fusion of four "core-shell" {Ti 4 @(TBC[8])(L)} subunits with four oxalate moieties. Notably, this cluster showcases an exceptional level of chemical stability, retaining its crystalline integrity even when immersed in highly concentrated acid (1 M HNO 3 ) and alkali (20 M NaOH). The macrocycle's surface unveils four specific, customizable μ 2 -bridging sites, primed to accommodate diverse carboxylate ligands. This adaptability is highlighted through deliberate modifications achieved by alternating crystal soaking in alkali and carboxylic acid solutions. Furthermore, Ti 16 L 4 macrocycles autonomously self-assemble into one-dimensional nanotubes, which subsequently organize into three distinct solid phases, contingent upon the specific nature of the four μ 2 -bridging ligands. Notably, the Ti 16 L 4 exhibit a remarkable capacity for photocatalytic activity in selectively reducing CO 2 to CO. Exploiting the macrocycle's modifiable shell yields a significant boost in performance, achieving an exceptional maximum CO release rate of 4.047 ± 0.243 mmol g -1 h -1 . This study serves as a striking testament to the latent potential of precision-guided surface ligand manipulation within robust clusters, while also underpinning a platform for producing microporous materials endowed with a myriad of surface functionalities.