Structure, UV-Vis Spectroscopy and Reactivity Properties of Melamine Metal(II) Complexes

Melamine is an important precursor of induced stones in the human kidney. Using density functional theory (DFT), conceptual DFT and time-dependent (TD) DFT, the structure, spectroscopy and reactivity properties of melamine (L) and its metal complexes ML2(OH)(2) (M=Ca, Mg, Fe, Cu, Zn, Ni) were systematically investigated in this work. We found that ML2(OH)(2) complexes were structurally and spectroscopically different from their precursors (L) and more reactive in electrophilic and nucleophilic reactions. A few quantitative linear relationships were discovered between bonding interactions, charge distributions, and DFT chemical reactivity indices with R-2=0.889-0.997, respectively. Results from frontier molecular orbital and electrostatic potential analyses show that ML2(OH)(2) systems from transition metal cations such as FeL2(OH)(2), CuL2(OH)(2) and NiL2(OH)(2) tend to be more covalently bound and they possess larger molecular twists and more electrophilic regions on the molecular contour surface. These results are believed to be implicative in our better understanding of the melamine stone production mechanism in the human body.