A new five-coordinated CuIP2NO2 system: XRD structure of 6-acetyl-1,3,7-trimethyl-pteridine-2,4(1H,3H)-dione and its Cu(I) (N5,O61,O4)-tridentate complex with triphenylphosphine. An AIM study of the nature of metal-ligand bonds.

The second example of a five-coordinated CuIP2NO2 system, [Cu(DLMAceM)(PPh3)2]ClO4 (DLMAceM=6-acetyl-1,3,7-trimethyl-pteridine-2,4(1H,3H)-dione), is reported. The structural characterization of both the DLMAceM ligand and the Cu(I) compound has been achieved by IR, 13C and 1H NMR and XRD methods. The metal is coordinated to the PPh3 molecules (Cu-P 2.224(2) and 2.258(2) A) and the pyrazine N(5) atom (Cu-N(5) 2.058(6) A) in a trigonal planar arrangement; two additional semi-coordinated atoms (Cu...O(4) 2.479(5) and Cu...O(61) 2.559(5) A) can be observed, forming an intermediate SP/TBP polyhedron. To define the nature of the metal-ligand bonds for the Cu(I) compound, especially in regards to the semi-coordinated oxygen atoms, a topological analysis of the electron density rhob within the framework provided by the quantum theory of atoms in a molecule (QTAIM) using Hartree-Fock and DFT(B3LYP) levels of theory has been performed. Five bond critical points (BCP) have been found, whose associated bond paths connect the Cu metal with the atoms P(1), P(2), O(4) O(61) and N(5). The type of interaction between the Cu and ligand binding sites has been characterized in terms of the Laplacian of the electron density, nabla2rhob, the total energy density, Hb, and the delocalization index, deltaAB.