First-principles calculations on the micro-solvation of 3d-transition metal ions: solvation versus splitting water.

Molecular level understanding of 3d-transition metal interaction with water molecules in various electronic states is of fundamental significance in chemistry and biology. This study systematically presents the propensity of 3d-transition metals in their variable electronic and spin states towards solvation and splitting water molecules. The topological analysis affirmed that neutral and mono-cationic complexes are prone to be partially covalent in nature from moving low to high spin states; however, coordinate bonding is observed in di- and tri-cationic ion–water complexes. Potential energy surface analysis showed a profound influence of electronic states of 3d-transition metals on the relative feasibility of bond scission and solvation competing pathways. The early neutral, high spin mono-cationic, and di-cationic transition metals prefer solvation over splitting the water molecule. Similarly, mid- and late-transition metal ions in the first two electronic states, irrespective of the spin state, show higher preferences towards solvation. In contrast, neutral and tri-cationic ions tend to form either insertion complexes, hydroxides, or hydrides over the ion–water complexes, suggesting a preference to split the water molecule. Thus, tuning the electronic and micro-environment will help in the design of transition metals catalysts for water splitting. [ABSTRACT FROM AUTHOR]