The Jahn-Teller effect in mixed aqueous solution: the solvation of Cu2+ in 18.6% aqueous ammonia obtained from ab initio quantum mechanical charge field molecular dynamics

The solvation structure and dynamics of Cu2+ in 18.6 % aqueous ammonia have been investigated using an ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation approach at the Hartree–Fock (HF) level of theory applying the LANL2DZ ECP and Dunning DZP basis sets for Cu2+, ammonia and water, respectively. During a simulation time of 20 ps, only NH3 molecules are observed within the first solvation shell of Cu2+, resulting in the formation of an octahedral [Cu(NH3)6]2+ complex. While no exchange of these ligands with the second solvation shell are observed along the simulation, the monitoring of the associated N-Ntrans distances highlight the dynamics of the associated Jahn-Teller distortions, showing on average 2 elongated axial (2.19 Å) and 4 equatorial Cu–N bonds (2.39 Å). The observed structural properties are found in excellent agreement with experimental studies. In addition, an NBO analysis was carried out, confirming the strong electrostatic character of the Cu2+–NH3 interaction.

Solution-phase electronegativity scale: insight into the chemical behaviors of metal ions in solution

By incorporating the solvent effect into the Born effective radius, we have proposed an electronegativity scale of metal ions in aqueous solution with the most common oxidation states and hydration coordination numbers in terms of the effective ionic electrostatic potential. It is found that the metal ions in aqueous solution are poorer electron acceptors compared to those in the gas phase. This solution-phase electronegativity scale shows its efficiency in predicting some important properties of metal ions in aqueous solution such as the aqueous acidities of the metal ions, the stability constants of metal complexes, and the solubility product constants of the metal hydroxides. We have elaborated that the standard reduction potential and the solution-phase electronegativity are two different quantities for describing the processes of metal ions in aqueous solution to soak up electrons with different final states. This work provides a new insight into the chemical behaviors of the metal ions in aqueous solution, indicating a potential application of this electronegativity scale to the design of solution reactions.

Hydration of highly charged ions

Based on a series of ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulations, the broad spectrum of structural and dynamical properties of hydrates of trivalent and tetravalent ions is presented, ranging from extreme inertness to immediate hydrolysis. Main group and transition metal ions representative for different parts of the periodic system are treated, as are 2 threefold negatively charged anions. The results show that simple predictions of the properties of the hydrates appear impossible and that an accurate quantum mechanical simulation in cooperation with sophisticated experimental investigations seems the only way to obtain conclusive results.