New Insights into the Jahn–Teller Effect through ab initio Quantum‐Mechanical/Molecular‐Mechanical Molecular Dynamics Simulations of Cu^II in Water

Abstract

The CuII hydration shell structure has been studied by means of classical molecular dynamics (MD) simulations including three-body corrections and hybrid quantum-mechanical/molecular-mechanical (QM/MM) molecular dynamics (MD) simulations at the Hartree-Fock level. The copper(II) ion is found to be six-fold coordinated and [Cu(H2O)6]2+ exhibits a distorted octahedral structure. The QM/MM MD approach reproduces correctly the experimentally observed Jahn-Teller effect but exhibits faster inversions (< 200 fs) and a more complex behaviour than expected from experimental data. The dynamic Jahn-Teller effect causes the high lability of [Cu(H2O)6]2+ with a ligand-exchange rate constant some orders or magnitude higher than its neighbouring ions NiII and ZnII. Nevertheless, no first-shell water exchange occurred during a 30-ps simulation. The structure of the hydrated ion is discussed in terms of radial distribution functions, coordination numbers, and various angular distributions and the dynamical properties as librational and vibrational motions and reorientational times were evaluated, which lead to detailed information about the first hydration shell. Second-shell water-exchange processes could be observed within the simulation time scale and yielded a mean ligand residence time of approximelty 20 ps.

Cuii in Liquid Ammonia: An Approach by Hybrid Quantum‐Mechanical/Molecular‐Mechanical Molecular Dynamics Simulation

“…Our recent work on Cu II in water yielded a coordination number of six [2] and a clearly defined Jahn ± Teller behavior (in agreement with many experimental results [1, 3±7] and in contrast to a previous Car ± Parrinello simulation of Pasquarello et al, which yielded a fivefoldcoordinated hydrate complex). [8] Numerous experimental investigations have been performed to determine the coordination of Cu II in liquid ammonia and some discrepancies concerning coordination number and geometry of solvates have remained unsolved to date.…”

Unraveling the Coordination Geometry of Copper(II) Ions in Aqueous Solution through Absorption Intensity

“…The geometrical description in terms of coupling to the a 2u mode has been implicitly observed through QM/MM molecular dynamics calculations, where the average equilibrium geometry (4 2.03 + 1 2.15 + 1 2.30 CuO distances), indeed reflects non-centrosymmetric a 2u distortions. [13,27] The fast dynamics associated with water ligands would be related to jumps among different configurational minima. Based on the absorption intensity of crystals and solution, we foresee that the initial Cu(H 2 O) 6 2+ complex, which would be stable at low temperature ( (Figure 2).…”

The hydration of Cu2+: Can the Jahn-Teller effect be detected in liquid solution?

“…13 On the theoretical side, contradictory results have been recently provided by molecular-dynamics ͑MD͒ simulations. While in one case, Blumberger et al 14 show that the Cu͑II͒ hydrate fluctuates between tetragonally distorted octahedral, square pyramidal, and trigonal bipyramidal coordination, in another case, Schwenk and Rode 15 support a single distorted octahedral structure. In the latter case, the existence of the standard JT distortion was derived from the appearance of a weak shoulder of the asymmetric peak at 2.17 Å in the RDF.…”

“…In the latter case, the existence of the standard JT distortion was derived from the appearance of a weak shoulder of the asymmetric peak at 2.17 Å in the RDF. 15 Amira et al 16 have recently proposed by means of Car-Parrinello MD computations a fivefold coordination exhibiting a square pyramid where the axial water molecule is elongated with respect to the four equatorial water molecules.…”