Structure and vibrational assignment of magnesium acetylacetonate: A density functional theoretical study

Abstract

Molecular structure of magnesium bis-acetylacetonate, Mg(acac) 2, has been investigated by means of ab initio and density functional theory (DFT) calculations and the results were compared with its gas-phase electron diffraction data. For comparison, the structure of Mg(acac) 2 was also optimized at the MP2 level using the 6-31G∗ basis set. The harmonic vibrational frequencies of Mg(acac) 2 were obtained at a variety of density functional theory levels using the 6-31G∗, 6-311G∗, 6-311++G∗∗, and lanL2DZ basis sets. The vibrational frequencies 2,4- 13C and 2- 13C derivatives of Mg(acac) 2 were also calculated at the B3LYP/6-311++G∗∗ level. The calculated frequencies are compared with the experimental Fourier transform IR and Raman spectra. All of the measured IR and Raman bands were interpreted in terms of the calculated vibrational modes. The scaled theoretical frequencies and the structural parameters are in excellent agreement with the experimental data. Analysis of the vibrational spectra indicates a strong coupling between the chelated ring modes. Four bands at the 1021, 664, 569, and 414 cm −1 are found to be mainly due to the metal oxygen stretching motions. The very strong Raman band at 414 cm −1 is assigned to the totally symmetric Mg O stretching mode. The corresponding band in beryllium bis-acetylacetonate, Be(acac) 2, appears at a considerably higher frequency (480 cm −1). This frequency difference is consistent with their different stability constants.