Highly Sorbent Films Derived from Ni(SCN)₂(4-picoline)₄ for the Detection of Chlorinated and Aromatic Hydrocarbons with Quartz Crystal Microbalance Sensors

A quartz crystal microbalance (QCM) spray-coated with a Ni(SCN)(2)(4-picoline)(4) film is a sensitive detector for small aromatic (benzene, toluene) and chlorinated (trichloroethylene, perchloroethylene) vapors with a planar molecular geometry. Frequency changes during transient exposures to these vapors are rapid and reversible. In contrast, frequency changes during transient exposures to carbon tetrachloride vapor exhibit a very slow rise and decay. Impedance studies demonstrate that the QCMs are responding only to mass changes in the film. Calibration curves exhibit both linear and near-saturation responses, depending on the vapor and vapor concentration. Partition coefficients obtained from the linear response regimes of the calibration curves are in the 10 000-100 000 range, more than an order of magnitude larger than the partition coefficients for a prototypical soft polymer, poly(isobutylene). Despite the absence of evidence for crystallinity by optical or X-ray diffraction methods, the spray-coated films appear to be forming clathrates with the organic vapors. The Ni(SCN)(2)(4-picoline)(4) film is promising for the development of very sensitive and partially selective piezoelectric sensors for nonpolar or weakly polar organic vapors in air.