Influence of substituent and ligand electronic factors on the measurement of gas phase olefins using a surface acoustic wave oscillator coated with trans-PtCl,( olefin) ( amine) complexes

Certain olefin gases and vapors can be measured selectively at low concentrations using surface acoustic wave (SAW) sensors vated with reagents of the general formula trans-PtClz(olefin)(amine). The sensor response depends on the steady-state rate of mass change associated with substitution of the initially complexed olefin by the free olefin analyte. This paper examines the effects of changes in the electronic nature of substituents on the free olefin and the olefin and amine ligands in the complex on the sensitivity and selectivity obtained with this class of SAW sensor coatings. For a given reagent, higher reaction rates are generally observed with electron-donating substituents on the double bond of the free olefin. For a given free olefin, varying the 4-substituent of the pyridine ligand in PtCl,(ethyleneX4-X-pyridine) gives a maximum response at an intermediate degree of amine basicity. Replacing pyridine by aniline, pyridine N-oxide or the 4-substituted derivatives of these ligands results in reduced responses for the olefins tested. Changing the initially complexed olefin leads to large changes in response, the pattern of which varies with the nature of the free olefin. Results demonstrate the potential for controlling the response of SAW sensors through subtle structural modifications of these coating reagents.