Potentiometric Anion Selectivity and Analytical Applications of Polymer Membrane Electrodes Based on Novel Mn(III)- and Mn(IV)-Salophen Complexes

New Mn(III)-L and Mn(IV)-L complexes were prepared from the highly lipophilic salophen ligand (L): phenol 2,2'-[(4,5-dimethyl-1,2-phenylene)bis[(E)-nitrilomethylidyne]]bis[4,6-bis(1,1-dimethylethyl). The prepared complexes were fully characterized and used for the construction of thiocyanate membrane electrodes. Optimized membrane electrodes contained 33.0 mg PVC, 66.0 mg o-nitrophenyloctylether, 50 or 5 (mole%) tetrakis(trifluoromethyl) phenyl borate and 1 mg Mn(III)-L (sensor 2) or Mn-(IV)-L (sensor 12), respectively. Such electrodes exhibited linear responses toward thiocynate in a concentration range of 10(-1)-10(-5) M and detection limits of 8.3 x 10(-6), 8.9 x 10(-6) M for sensor 2 and 12, respectively. Optimized membrane electrodes exhbited high selectivty toward thiocayante compared to more lipophilic anions. The observed thiocyanate selectivity of the optimized membranes was confirmed by formation constant calculations for Mn(III)-L and Mn(IV)-L with SCN-, beta=10(14.1) and 10(12.5), which was measured potentiometrically using the sandwich membrane method. Furthermore, computational study using DFT calculations was performed to at DFT/B3LYP level of theory to confirm the observed selectivity data. The response times were 3 and 0.5 min for low and high concentrations. The lifetimes of the optimized electrodes were similar to 4-6 weeks. The analytical utility of the optimized membrane electrodes was demonstrated by the analysis of thiocyanate level in different saliva samples.