Effect of water on zinc (II), cadmium (II) complexes with pyridylimidazole: Theoretical study of stability and electronic spectrum

The geometry structures of complexes such as [Zn(PIm)₂(H ₂O)] and [Cd(PIm)₂(H₂O)₂] [PIm = (2-(2′-pyridyl) imidazole)] are optimized by density functional theory (DFT) B3LYP methods. On the basis of their stable structures, the stability of the coordinated water existing in the complexes is analyzed quantitatively in terms of the interaction between the central metal and the coordinated water. The interaction energy of the Zn pyridylimidazole complex increased obviously by considering the intermolecular hydrogen bond (O-H⋯N). The theoretical calculation well explained penta- and hexa-coordinated conformation, respectively, in Zn and Cd pyridylimidazole complexes. The spectral properties of the Zn Cd complexes have been studied by time-dependent density functional theory (TD-DFT). The calculation results show that the coordinated waters in Cd complexes have little effect on their spectral properties. While the axially coordinated waters in Zn pyridylimidazole cause a red shift in the absorption wavelength and change the pattern of charge transfer as a result of the effect of polarization from intermolecular hydrogen bond.