A density functional theory investigation of the interaction of the tetraaqua calcium cation with bidentate carbonyl ligands.
Calcium complexes with bidentate carbonyl ligands are important in biological systems, medicine and industry, where the concentration of Ca2+is controlled using chelating ligands. The exchange of two water molecules of [Ca(H2O)6]2+for one bidentate monosubstituted and homo disubstituted dicarbonyl ligand was investigated using the B3LYP/6-311++G(d,p) method. The ligand substituents NH2, OCH3, OH, CH3, H, F, Cl, CN and NO2are functional groups with distinct electron-donating and -withdrawing effects that bond directly to the sp2C atom of the carbonyl group. The geometry, charge and energy characteristics of the complexes were analyzed to help understand the effects of substituents, spacer length and chelation. Coordination strength was quantified in terms of the enthalpy and free energy of the exchange reaction. The most negative enthalpies were calculated for the coordination of bidentate ligands containing three to five methylene group spacers between carbonyls. The chelate effect contribution was analyzed based on the thermochemistry. The electronic character of the substituent modulates the strength of binding to the metal cation, as ligands containing electron-donor substituents coordinate stronger than those with electron-acceptor substituents. This is reflected in the geometric (bond length and chelating angle), electronic (atomic charges) and energetic (components of the total interacting energy) characteristics of the complexes. Energy decomposition analysis (EDA)-an approach for partitioning of the energy into its chemical origins-shows that the electrostatic component of the coordination is predominant, and yields relevant contribution of the covalent term, especially for the electron-withdrawing substituted ligands. The chelate effect of the bidentate ligands was noticeable when compared with substitution by two monodentate ligands. Graphical abstract The affinity of 18 bidentate carbonyl ligands toward the [Ca(H2O)4]2+cation is evaluated in terms of energetic, geometric and electronic parameters of the isolated ligands and the substituted aqua complexes. The electronic effects-inductive and mesomeric-intrinsic to the molecular structure of each ligand are found to modulate the strength of the metal-ligand interaction. The effects of polysubstitution, chelation and the length of the alkyl spacers between the anchor points of the ligand are also analyzed.
Programa de Pós-Graduação em Química, Universidade Federal Fluminense, Outeiro de São João Batista, s/n, 24020-141, Niterói, RJ, Brazil.
Daniel Garcez S
DG
Quattrociocchi
Faculdade de Farmácia, Universidade Federal Fluminense, Rua Mario Viana 523, 24241-000, Niterói, RJ, Brazil.
Marcos Vinicius Monsores
MV
Meuser
Programa de Pós-Graduação em Química, Universidade Federal Fluminense, Outeiro de São João Batista, s/n, 24020-141, Niterói, RJ, Brazil.|Departamento de Química Inorgânica, Universidade Federal Fluminense, Niterói, RJ, Brazil.
Glaucio Braga
GB
Ferreira
Programa de Pós-Graduação em Química, Universidade Federal Fluminense, Outeiro de São João Batista, s/n, 24020-141, Niterói, RJ, Brazil.|Departamento de Química Inorgânica, Universidade Federal Fluminense, Niterói, RJ, Brazil.
José Walkimar
JW
de M Carneiro
Natural Resources Canada, Canmet ENERGY-Devon, 1 Oil Patch Drive, Devon, AB, T9G 1A8, Canada. stanislav.stoyanov@canada.ca.|Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 2V4, Canada. stanislav.stoyanov@canada.ca.
Stanislav R
SR
Stoyanov
Programa de Pós-Graduação em Química, Universidade Federal Fluminense, Outeiro de São João Batista, s/n, 24020-141, Niterói, RJ, Brazil. lmcosta@id.uff.br.|Programa de Pós-Graduação em Ciência e Tecnologia Ambiental, Centro Universitário Estadual da Zona Oeste, Av. Manuel caldeira de Alvarenga, 1203, 23070-200, campo Grande, RJ, Brazil. lmcosta@id.uff.br.|Departamento de Química Orgânica, Universidade Federal Fluminense, Niterói, RJ, Brazil. lmcosta@id.uff.br.
Leonardo Moreira
LM
da Costa
Bidentate carbonyl ligands; Ca2+ cation; Chelate effect; Density functional theory (DFT); Energy decomposition analysis; Inorganic scaling; Ionophore