Unlike chemical bonds present in organic molecules, compounds containing transition metals shows a synergism in its bonds with the ligands present in their coordination spheres which are essential to the reactivity of these compounds. The metal-ligand interactions in the first coordination sphere will determine the properties of these compounds and impact on the absorption and emission spectroscopies thereof. The challenge comes from the fact that transition metals usually have unpaired electrons in orbitals and the interaction with a given ligand can lead to complexes with different spin multiplicities showing different reactivity and spectroscopic properties. Modern Methods of electronic structure calculations, in conjunction with electron density analysis methods have been used in our group for understanding the nature of the metal-ligand interactions and to understand the spectroscopic properties of organometallic compounds and metal complexes.
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Representative publications:
da Silva, J. C. S.; Rocha, W. R. Insights into the coordination chemistry of alkanes to metal carbonyls from quantum chemical calculations. J. Organomet. Chem. 2015, 793, 241–247. 
Aguilar, C. M.; Rocha, W. R. The nature of the M–NO bond in [M(Imidazole)(PPIX)(L)]q complexes (M=Fe2+, Ru2+; L=NO+, NO and NO−; PPIX=Protoporphyrin IX). Inorganica Chim. Acta 2013, 408, 18–26.
Chagas, M. A.; Rocha, W. R. Solvent effects on the metal-to-ligand charge transfer transition of the complex [Ru(NH3)5(Pyrazine)]2+. Chem. Phys. Lett. 2014, 612, 78–83.
Ferreira, D. E. C.; De Almeida, W. B.; Neves, A.; Rocha, W. R. Broken symmetry density functional study of biomimetic models for Purple Acid Phosphatases of the type Fe(III)–M(II) (M=Fe, Cu, Ni, Co and Mn). Comput. Theor. Chem. 2012, 979, 89–95.
Da Silva, J. C. S.; De Almeida, W. B.; Rocha, W. R. Theoretical investigation of the structure and nature of the interaction in metal–alkane σ-complexes of the type [M(CO)5(C2H6)] (M=Cr, Mo, and W). Chem. Phys. 2009, 365 (1–2), 85–93.
Ferreira, D. E. C.; De Almeida, W. B.; Neves, A.; Rocha, W. R. Broken symmetry density functional study of a mixed-valence unsymmetrical dinuclear iron complex. Int. J. Quantum Chem. 2009, 110 (5), 1048-1055.
Aguilar, C. M.; De Almeida, W. B.; Rocha, W. R. Solvation and electronic spectrum of Ni2+ ion in aqueous and ammonia solutions: A sequential Monte Carlo/TD-DFT study. Chem. Phys. 2008, 353 (1–3), 66–72.