Structures, binding and clustering energies of Cu2+(MeOH)n=1-8 clusters and temperature effects: A DFT study

The study of Cu2+-methanol interactions allows the understanding of metal-alcohol interactions present in many biological and biochemical processes. This work proposes to explore the potential energy of surfaces of the Cu2+(MeOH)(n=1-8) clusters in gas phase, temperature-dependence of the relative population, binding and clus-tering energies of the solvated Cu2+ ion in methanol using M06-2X DFT functional method associated with the 6-31++G** basis set. It emerges new structures are presented for the first time in the literature and the stability rules are respected in almost all sizes. Moreover, the comparison of the length distances of dative bonds obtained with the M06-2X method are in agreement with the experimental results and with the ab initio MP2 method. The M06-2X method is thus presented as an alternative to the MP2 method. The investigation of the temperature dependence of the isomer distribution shows that the most stable and compact structures dominate the population of the studied clusters. For sizes n = 2-4, two isomers contribute to the relative population with a dominance of structures in which the methyl group is symmetric, particularly at low temperature. For n >= 6, at least three isomers participate in the population of clusters. Thus, the hexa-, penta-and tera-coordinated structures compete the population of clusters. We also predicted binding and clustering energies as a function of the cluster size, up to n = infinity. We propose new values of the electronic binding energy, the binding enthalpy and the free binding energy for the solvation of the Cu2+ ion in methanol. These values are respectively -7150.3, -5974.3 and -4069.5kJ mol(-1). Similarly, the values of clustering energies, clustering enthalpy and clustering free energy of Cu2+(MeOH)(n) clusters, are -113.5,-115.8 and -47.9kJ mol(-1) respectively. These energy analyzes are in agreement with the MP2 results and the experimental results obtained in methanol with other dications.