Lanthanide coordination compounds modeling: Sparkle/PM3 parameters for dysprosium (III), holmium (III) and erbium (III)

The Sparkle model, recently parameterized for all trivalent lanthanide ions using the AM1 semiempirical quantum chemical model, is now parameterized to PM3 method. In a recent paper [R.O. Freire, G.B. Rocha, A.M. Simas, Chem. Phys. Lett. 425 (2006) 138] we defined the Sparkle/PM3 model for Tm(III). Now the Sparkle/PM3 is extend to dysprosium (III), holmium (III) and erbium (III) ions. In the parameterization procedure, we used the same three sets of 15 complexes used to parameterize Sparkle/AM1 for each of these three lanthanide ions, with various representative ligands. The Sparkle/PM3 unsigned mean error, for all interatomic distances between the trivalent lanthanide ion and the ligand atoms of the first sphere of coordination, is 0.072 Å for Dy(III); 0.064 Å for Ho(III); and 0.072 Å for Er(III). These figures are similar to the Sparkle/AM1 ones of 0.066 Å, 0.054 Å, and 0.064 Å, respectively, indicating they are all comparable parameterizations. Moreover, their accuracy is similar to what can be obtained by present-day ab initio effective core potential calculations on such lanthanide complexes. Hence, the choice of which model to use remains with the researcher who must evaluate the impact of either AM1 or PM3 on the quantum chemical description of the organic ligands.