Raman Detected Sensing of Volatile Organic Compounds by Vapochromic Cu[AuX2(CN)2]2 (X = Cl, Br) Coordination Polymer Materials

Two vapochromic coordination polymers Cu­[AuX2(CN)2]2 (X = Cl, 1; X = Br, 2) were prepared and spectroscopically characterized. Exposure of these solid materials to the volatile organic compounds dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, 1,4-dioxane, and ethylene glycol (glycol) resulted in distinct color, and IR and Raman changes. The thermal stability of the analyte-bound materials was assessed by thermogravimetric analysis. Single-crystal structures of Cu­(analyte)4[AuX2(CN)2]2 (analyte = DMF, DMSO; X = Cl, Br) revealed an isostructural set of 1-D coordination polymer chains, where the analyte molecules were equatorially O-bound to the Cu­(II) centers while axially bound [AuX2(CN)2]− units bridged these Cu­(II) centers, while Cu­(glycol)4[AuBr2(CN)2]2 is molecular, with monodentate glycol units. The structure of Cu2(OH2)4[AuCl2(CN)2]4·4dioxane is a 2-D coordination polymer network with H2O-bridged Cu­(II) centers and dioxane units hydrogen bonded between the 2-D sheets. The intense Raman vCN stretches for 1, 2, and their adducts form distinct, signature patterns. These “antenna” Raman vCN stretches are an effective means for sensing VOCs, and their characteristic patterns can be used to identify the VOC being detected.