Fourier transform infrared spectrum: Vibrational assignments using density functional theory and natural bond orbital analysis of the bis(guanidoacetate)nickel(II) complex

Theoretical and experimental band assignments for the Fourier transform infrared spectrum of the [Ni(GAA)(2)] center dot 2 H2O (bis(guanidoacetate)nickel(11) complex) trans isomer has been made based on the DFT: B3LYP/6-311G(d,p) procedure, second derivative spectrum, and band deconvolution analysis. Bond orbital analysis was used to determine the effect of electronic delocalization involving Ni-O and Ni-N bonds and their neighbour groups. Also, natural bond orbital analysis was extended to Ni-O and Ni-N interactions, indicating in both cases that the sp(2.01)d(1.01) Ni(II) hybridization is adequate for the planar stricture around the Ni(II) cation. The calculated infrared spectrum, based On the proposed geometrical structure of the trans bis(guanidoacetate)nickel(II) complex without crystallization water, shows an excellent agreement with the experimental spectrum, and matches better than the calculated spectra for the [Ni(GAA)(2)] cis isomer. The calculated energy for the [Ni(GAA)(2)] trans isomer complex is 21.75 kcal/mol more stable than that of the cis isomer.