title: The importance of the oxidative character of doubly charged metal cations in binding neutral bases. [Urea-M]2+ and [thiourea-M]2+ (M = Mg, Ca, Cu) complexes.
abstract: Different analysis of the electron density, namely AIM, ELF and NBO, yield coherent descriptions of the bonding in [urea-M](2+) and [thiourea-M](2+) (M = Mg, Ca, Cu) complexes, whose geometries have been optimized at the B3LYP/6-311+G(d,p) level of theory. The interactions of these two bases with the alkaline-earth dications are essentially electrostatic, whereas the bonding with Cu(2+) has a non-negligible covalent character. As a consequence and in spite of the fact that Cu(2+) has practically the same ionic radius as Mg(2+), the calculated Cu(2+) binding energies are about 1.5 and 2 times larger than Mg(2+) and Ca(2+) binding energies, respectively. The main difference, however, between Mg(2+) or Ca(2+) with respect to Cu(2+) complexes is due to the fact that Cu(2+) is able to oxidize the base. Hence, both [urea-Cu](2+) and [thiourea-Cu](2+) complexes can be viewed as the interaction between urea(+*) or thiourea(+*) radical cations and Cu(+).
authors.affiliation: Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Trujillo
authors.forename: Al Mokhtar
authors.initials: AM
authors.lastname: Lamsabhi
authors.forename: Otilia
authors.initials: O
authors.lastname: Mó
authors.forename: Manuel
authors.initials: M
authors.lastname: Yáñez
mesh_terms: D002118:Calcium / Q000737:chemistry*; D002412:Cations; D002627:Chemistry, Physical / Q000379:methods*; D003300:Copper / Q000737:chemistry*; D004583:Electrons; D006860:Hydrogen Bonding; D007477:Ions; D008274:Magnesium / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry*; D013890:Thiourea / Q000737:chemistry; D014508:Urea / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D002412:Cations; D007477:Ions; D008670:Metals; D014867:Water; D003300:Copper; D014508:Urea; D013890:Thiourea; D008274:Magnesium; D010100:Oxygen; D002118:Calcium