Beyond Structural Analogy: Electronic and Functional Divergence in Isostructural Zr, Hf, and Th Metal–Organic Frameworks

Zr(IV), Hf(IV), and Th(IV) exhibit closely related coordination chemistry and can form structurally analogous materials, underpinning the widespread use of Zr as a nonradioactive surrogate for Th(IV). Here we demonstrate that such structural analogy does not necessarily extend to electronic and functional properties through a comparative study of three isostructural M6-ADC (M = Zr, Hf, and Th;ADC = 9,10-anthracenedicarboxylate) metal–organic frameworks. Despite their nearly identical framework structures, Th6-ADC exhibits optical and electronic characteristics distinct from its Zr and Hf analogues, including distinctive red coloration, extended visible-to-near-infrared absorption, and a pronounced ligand-centered radical signature. These electronic differences are further manifested in their functional behavior, with Th6-ADC displaying substantially enhanced photothermal conversion under near-infrared irradiation. These results reveal a clear divergence between structural and electronic similarity among Zr-, Hf-, and Th-based frameworks.