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 k3-like conformation, thus indicating that, even though frequently observed, the k3-tripodal coordinative mode is unlikely to be directly achieved through the interaction of M(I) with the k3-like tpm conformer. It is also found that the energy barrier for the k2-[M(tpm)]+ → k3-[M(tpm)]+ conversion is negligible. As far as the bonding scheme is concerned, the tpm → M(I) donation, both σ and π 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 π* levels plays a negligible role.