Achieving High-Sensitivity and High-Selectivity Nitric Acid Vapor Sensors at Room Temperature: A Mixed-Ligand Cu2I2(P-( m -Tol)3)2(4VP)2 Cluster

Nitric acid (HNO3) vapor is highly corrosive and hazardous yet developing room-temperature chemiresistive sensors for its sensitive and selective detection remains challenging. Herein, we report a mixed-ligand copper iodide cluster, Cu2I2(P-(m-Tol)3)2(4VP)2, as a molecularly engineered sensing material for HNO3 vapor detection. The incorporation of complementary phosphine and pyridine ligands simultaneously enhances the structural stability of the copper(I) iodide framework and provides accessible recognition sites for acidic gas molecules. The chemiresistive sensor exhibits excellent HNO3 sensing performance at room temperature, delivering a high response of 925% toward 100 ppm of HNO3, low theoretical limit of detection of 235 ppb and limit of quantitation of 784 ppb, rapid response/recovery times of 13/8.8 s, as well as outstanding selectivity, humidity tolerance and cycling stability. Density functional theory calculations reveal that HNO3 are anchored on the cluster surface via cooperative dual-site adsorption involving an O–H···I hydrogen-bond-like interaction and an O···H–C interaction with the 4VP ligand. The cooperative adsorption mode induces interfacial charge redistribution, accompanied by electron transfer from the n-type cluster to HNO3 molecules, thereby modulating the electrical resistance. This work establishes a molecular-level relationship between ligand regulation, acidic gas recognition, and chemiresistive response, providing a rational strategy for cluster-based sensors for highly corrosive gas detection.