Density functional theory study of the binding capability of tris(pyrazol-1-yl)methane toward Cu(I) and Ag(I) cations

Density functional theory (DFT) has been used to look into the electronic structure of [M(tpm)](+) molecular ion conformers (M = Cu, Ag; tpm = tris(pyrazol-1-yl)methane) and to study the energetics of their interconversion. Theoretical data pertaining to the free tpm state the intrinsic instability of its kappa(3)-like conformation, thus indicating that, even though frequently observed, the kappa(3)-tripodal coordinative mode is unlikely to be directly achieved through the interaction of M(I) with the kappa(3)-like tpm conformer. It is also found that the energy barrier for the kappa(2)-[M(tpm)](+) -> kappa(3)-[M(tpm)](+) conversion is negligible. As far as the bonding scheme is concerned, the tpm -> M(I) donation, both sigma and pi in character, is the main source of the M(I)-tpm bonding, whereas back-donation from completely occupied M(I) d orbitals into tpm-based pi* levels plays a negligible role.