A combined experimental and quantum mechanical investigation on some selected metal complexes of l-serine with first row transition metal cations

• Solid phase metalation of l-serine under solventless conditions.
• Ab initio- and density-functional studies of metalated l-serine.
• Effectiveness of the BHandHLYP functional for Cu+2 complexes.

In the current study a joint solvent-free synthetic and computational approach has been adopted to explore the coordination properties of l-serine with the doubly charged cations of nickel, copper and zinc. The reaction products were characterized by elemental analyses, molar conductance, EDAX–SEM, TEM, TG/DTA, infrared, electronic absorption and fluorescence spectroscopy. Quantum chemical calculations, carried out in gas and aqueous phase using the BHandHLYP and MP2 methods in conjunction with 6-311++G(d,p) basis set, provide valuable insights concerning the interaction enthalpies and free energies; vibrational and absorption spectra along with various other molecular and electronic properties of the metal complexes. This study reveals that l-serine binds to the metal ions in a bi-dentate manner through its amino and carboxylate groups exhibiting highest binding affinity towards Cu(II) among the three metal ions considered here. As compared to the MP2 method, the spin-delocalized situations of the open-shell Cu(II) complex of l-serine have been better described at the BHandHLYP level. The physical origin of the molecular interactions of l-serine with the metal ions has also been examined by performing energy decomposition analysis (EDA). Effects of the aqueous environment are evident on the structure and stability of the metal complexes. The vibrational spectroscopic data furnished at MP2/6-311++G(d,p) level, which provide a good account of the structural changes inflicted in the molecular geometry of l-serine as a result of metal coordination, are in better agreement with our experimental observations as compared to those produced at the BHandHLYP/6-311++G(d,p) level.

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