Spectroscopic studies of ion-solvation and ligand-metal coordination: Towards surface spectroscopy.

摘要

A spectroscopic study of ion solvation in LiClO4, NaClO 4, and tetraethylammonium perchlorate-acetonitrile solutions was performed using attenuated total reflection (ATR) FTIR spectroscopy. It was demonstrated that the C≡N stretching band of acetonitrile molecules associated with C1O4-- has a significantly different molar absorption coefficient from that band of self-associated acetonitrile. The spectra of the LiClO4, and NaClO4, solutions were shown to be a linear combination of one basis spectrum that accounts for self-associated acetonitrile molecules and another that accounts for the acetonitrile molecules associated with cations and ClO4--.;Solutions of AlCl3 with picolinate (2-pyridinecarboxylate), quinolinate (2,3-pyridinedicarboxylate), or phthalate (1,2-benzenedicarboxylate) were investigated using ATR-FTIR spectroscopy, 27Al-NMR, and potentiometry. The infrared spectra of the protonation states of each ligand were isolated by a factor analysis and assigned. The 27Al-NMR spectra of the solutions containing the picolinate and quinolinate ligands were analyzed to determine the concentrations of the Al(H2O) 63+ species and the Al(III)-ligand complexes. These data were subsequently fit with a speciation model in order to determine the conditional formation constants of the Al(III)-ligand complexes. The infrared spectra of the protonation states of the ligand and the results of the 27Al-NMR speciation analysis were used to constrain the infrared spectra of the Al(III)-ligand solutions and isolate the spectra of the Al(III)-ligand complexes. The assignment of the spectra of these complexes indicates that both picolinate and quinolinate coordinate to Al(III) through the nitrogen of the pyridine ring and one oxygen of a carboxylate substituent. A speciation model could not be determined that would explain the 27Al-NMR spectra of the solutions containing the plithalate ligand, and therefore the infrared spectra of the Al(III)-phthalate complexes could not be isolated.;Overlayer attenuated total reflectance (O-ATR) infrared spectroscopy was evaluated as a surface analytical tool for investigating adsorbates at surfaces exposed to aqueous solutions. Through modeling an O-ATR system by assuming it to be comprised of either three, four, or n phases of homogeneous refractive index, an electric-field analysis was used to determine how surface specificity and signal-to-noise depend on adsorption free energy, overlayer thickness, angle of incidence, and the refractive index of the internal-reflection element.