Eliminating Aromaticity Unlocks Broad and Enhanced Areal Negative Thermal Expansion in Metal–Organic Frameworks

Metal–organic frameworks (MOFs) combine structural flexibility with chemical tunability, offering an ideal platform for engineering extreme thermal expansion behavior. Herein, we report two nearly isostructural ytterbium tricarboxylates, Yb-BTC (BTC = 1,3,5-benzenetricarboxylate) and Yb-CTC (CTC = 1,3,5-cyclohexanetricarboxylate), that exhibit rare areal negative thermal expansion (NTE). Intriguingly, replacing the aromatic BTC ligand with its non-aromatic CTC analogue can simultaneously broaden and strengthen the NTE response. The Yb-CTC shows NTE over an ultrawide temperature range from 100 to 900 K, surpassing most inorganic ceramics and setting a benchmark for MOF-based NTE materials. Comprehensive experimental and theoretical investigations reveal that this enhancement arises from two cooperative effects: stronger Yb–O coordination significantly improves thermal stability, while the reduced carboxylate rotational barrier introduces abundant low-frequency phonons with negative Grüneisen parameters. These synergistic effects demonstrate a new strategy for regulating NTE in MOFs, enabling simultaneous control over both temperature range and contraction magnitude.