Tris(pyrazol-1-yl)borate and tris(pyrazol-1-yl)methane: A DFT study of their different binding capability toward Ag(I) and Cu(I) cations

Density functional theory has been used to study the electronic structure of [M(tp)] and [M(tpm)](+) conformers (M = Cu, Ag; tp = tris(pyrazol-1-yl)borate anion, tpm = tris(pyrazol-1-yl) methane) and the energetics of their interconversions. Results for the free tp ligand are similar to those of tpm [M. Casarin, D. Forrer, F. Garau, L. Pandolfo, C. Pettinari, A. Vittadini, J. Phys. Chem. A 112 (2008) 6723], indicating an intrinsic instability of the tripodal conformation (kappa(3)-like). This points out that, though frequently observed, the kappa(3)-coordinative mode is unlikely to be directly achieved through the interaction of M(I) with the kappa(3)-like tp/tpm conformer. Analogously to the [M(tpm)](+) molecular ions, the energy barrier for the kappa(2)-[M(tp)] -> kappa(3)-[M(tp)] conversion is computed to be negligible. Though kappa(n)-[M(tp)] and kappa(n)-[M(tpm)](+) (n = 1, 2, 3) have similar metal-ligand covalent interactions, the negative charge associated to the tp ligand makes the M-tp bonding stronger.