Atomic-scale origin of charge density wave-driven metal-semiconductor transition in an incommensurately modulated metal-organic framework

TL;DR

This study directly links atomic-scale structural modulation to a macroscopic metal-semiconductor transition in a metal-organic framework, revealing the electronic origin of charge density waves at the atomic level.

Contribution

First direct resolution of incommensurate structural modulation in a conductive metal-organic framework linked to electronic phase transition.

Findings

Reversible metal-semiconductor transition at 350 K coincides with disappearance of structural modulation.

Structural modulation stabilized by guest water molecules affecting inter-linker interactions.

Established experimental criterion for one-dimensional charge density wave in metal-organic frameworks.

Abstract

The intrinsic incommensurate charge density wave in metal-organic frameworks has remained elusive due to the lack of direct evidence linking atomic-scale structural modulation to macroscopic electronic properties. Using high-quality Pr3HHTP2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) single crystals as a model system, we precisely resolve, for the first time, the incommensurately modulated structure of a conductive metal-organic framework at 100 K (modulation vector q = 0.39143(12) c*) via temperature-dependent single-crystal X-ray diffraction. The subsequent observation of a reversible metal-semiconductor transition around 350 K, which perfectly synchronizes with the disappearance of the structural modulation, provides convincing evidence for the electronic origin of the lattice distortion. Guest water molecules stabilize the modulated phase by synergistically regulating the relative rotation of the linkers and the interlayer spacing, thereby optimizing the inter-linker interactions. This work establishes a concrete experimental criterion for one-dimensional charge density wave in metal-organic frameworks and provides an ideal platform for probing coupled electronic-lattice modulations.