Theoretical analysis of the oxocarbons: The solvent and counter-ion effects on the structure and spectroscopic properties of the squarate ion

Abstract

The squarate anion and their coordination compounds with Li⁺, Na⁺ and K⁺ are studied in gas phase and aqueous solution using ab initio quantum chemical methods and a sequential Monte Carlo/quantum mechanical procedure. The infrared and Raman spectra were calculated and the vibrational modes assigned at the second order Møller–Plesset perturbation (MP2) level of theory, employing standard split-valence basis set with inclusion of polarization and diffuse functions (6-31G(d), 6-31+G(d), 6-311+G(d), 6-311+G(2d), 6-311+G(2df)) on the O and C atoms. The vibrational analysis showed an important role played by the polarization functions on the low frequency vibrations. The solvent and counter-ions effects on the electronic spectrum are analyzed showing that both should be included in the calculation in order to reproduce the observed UV spectrum. This conclusion supports our previous analysis on the oxocarbon series.