New complexes of guanidinewith acetic, trichloroacetic and trifluoroacetic acids - The DFT structural and vibrational investigations

The density functional theory (DFT) methods were used for theoretical studies of three compounds. The guanidine molecule is a main structural unit in these complexes, while the studied acids have similar chemical character. The family of simple guanidinium compounds is intensively investigated as potential materials with ferroic phase transitions. Among studied guanidinium complexes, those with crystal structure without macroscopic center of inversion, exhibit NLO properties. For three compounds: CN3H5CH3COOH, CN3H5CCl3COOH and CN3H5CF3COOH the detailed theoretical calculations were performed. For each complex the equilibrium geometry was obtained. The calculated geometrical parameters (bond lengths and angles) of all investigated complexes are compared. The theoretical vibrational frequencies and potential energy distribution (PED) of three guanidinium compounds were calculated by B3LYP method. On the basis of PED calculations the detailed assignments of bands for new chemical complexes are presented. The real crystals were obtained in the case of CN3H5CH3COOH compound, only. The theoretical results can be used in future, when the synthesis of trichloroacetic and trifluoroacetic analogues of CN3H5CH3COOH will be done. (c) 2007 Elsevier B.V. All rights reserved.