Ligand-Directed Valence Band Engineering in Pb²⁺ Hybrid Crystals: Achieving Dispersive Bands and Shallow Valence Band Maximum

While crystalline hybrid solids hold great potential as novel semiconductors, most semiconductive hybrids utilize transition metal ions, which inherently limit carrier mobility due to the small band dispersion derived from the d orbitals. The filled s orbitals of post-transition metal ions offer the potential to design dispersed valence bands, but a method to translate the local structure design of these metal ions to valence band engineering is still in development. This study focuses on Pb²⁺-containing hybrid crystals, developing a simple strategy to control the Pb²⁺ coordination geometry through the molecular design of azole ligands. By preprogramming the coordination number of Pb²⁺ with azolate ligands, we succeeded in obtaining an isotropic coordination environment at a higher coordination number, resulting in a dispersed valence band and shallow valence band maximum while having a wide band gap. Detailed analysis of the band structures reveals that the energy levels and symmetry of the molecular orbitals of the anions play important roles in realizing these antinomic properties. This ligand-directed approach achieves both isotropy and covalency in the coordination bond by exploiting the diversity of the molecular orbitals. Our findings provide a foundation for future design strategies to optimize electronic structures in hybrid materials, advancing their application in semiconductive devices.