A PN(Pz)P ligand protected Au2Cu2 complex for photoluminescent ultra-low humidity detection with reversible single-crystal-to-single-crystal transformations

Abstract

Reliable and sensitive detection of sub-ppm level, ultra-low humidity is critical for a number of important technologies. We herein report the reaction of a P/N hybrid ligand 3-dppmapz-1-ol with Au(I) and Cu(I) salts resulting in a heteronuclear Au₂Cu₂ cluster complex [Au₂Cu₂(3-dppmapz)₂](PF₆)₂·4MeOH (1·4MeOH) that undergoes reversible single-crystal-to-single-crystal (SCSC) transformations into analogues 1 and 1·2H₂O. The photoluminescent emission of 1·2H₂O at 625 nm shifted to 617 nm within 24 h and 622 nm after 65 h in P₂O₅ dried air, and returned to green in MeOH/H₂O or MeOH/EtOH vapour. Crystals of 1 could rapidly detect ultralow humidity of 0.21 ppm (w/w).