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[AuX 2 (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 [AuX 2 (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 [AuX 2 (CN) 2 ] − units bridged these Cu(II) centers, while Cu(glycol) 4 [AuBr 2 (CN) 2 ] 2 is molecular, with monodentate glycol units. The structure of Cu 2 (OH 2 ) 4 [AuCl 2 (CN) 2 ] 4 ·4dioxane is a 2-D coordination polymer network with H 2 O-bridged Cu(II) centers and dioxane units hydrogen bonded between the 2-D sheets. The intense Raman v CN stretches for 1, 2, and their adducts form distinct, signature patterns. These “antenna” Raman v CN stretches are an effective means for sensing VOCs, and their characteristic patterns can be used to identify the VOC being detected.