Unconventional Heterobidentate Coordination of 4‐Hydroxypyridine Leading to Remarkably Strong Second‐Harmonic Generation in Zn(C5H4NO)2

Herein, we report an unconventional heterobidentate coordination mode of conventional 4-hydroxypyridine ligand in a novel compound Zn(C₅H₄NO)₂. The strong heterobidentate coordination interactions between Zn²⁺ and 4-hydroxypyridine ligands promote a uniform alignment of the polarization of each [ZnO₂N₂] tetrahedral building unit, resulting in remarkably strong second-harmonic generation (SHG) with an intensity that is the largest among all UV-transparent Zn-containing metal-organic compounds reaching 13.6×KDP. Moreover, Zn(C₅H₄NO)₂ processes a suitable optical band gap of 4.40 eV, high thermal stability up to 300 °C, excellent air stability, and strong water resistance, demonstrating great application potential. Additionally, Zn(C₅H₄NO)₂ exhibits photoluminescence with a significantly enhanced lifetime of 558 ms, accompanied by a rare blue afterglow visible to the naked eye, lasting up to 5 s.