Electronic Structure of 3d [M(H₂O)₆]³⁺ Ions from Sc^III to Fe^III:  A Quantum Mechanical Study Based on DFT Computations and Natural Bond Orbital Analyses

Abstract

The metal-donor atom bonding along the series of 3d[M(H2O)6](3+) ions from Sc(3+) to Fe(3+) has been investigated by density-functional calculations combined with natural localized bond orbital analyses. The M-OH(2) bonds were considered as donor-acceptor bonds, and the contributions coming from the metal ion's 3d sigma-, 3d pi-, and 4s sigma-interactions were treated individually. In this way, the total amount of charge transferred from the water oxygen-donor atoms toward the appropriate metal orbitals could be analyzed in a straightforward manner. One result obtained along these lines is that the overall extent of ligand-to-metal charge transfer shows a strong correlation to the hydration enthalpies of the aqua metal ions. If the contributions to the total ligand-to-metal ion charge transfer are divided into sigma- and pi-contributions, it turns out that Cr(3+) is the best sigma-acceptor, but its pi-accepting abilities are the weakest along the series. Fe(3+) is found to be the best pi-acceptor among the 3d hexaaqua ions studied. Its aptitude to accept sigma-electron density is the second weakest along the series and only slightly higher than that of Sc(3+) (the least sigma-acceptor of all ions) because of the larger involvement of the Fe(3+) 4s orbital in sigma-bonding. The strengths of the three types of bonding interactions have been correlated with the electron affinities of the different metal orbitals. Deviations from the regular trends of electron affinities along the series were found for those [M(H2O)6](3+) ions that are subject to Jahn-Teller distortions. In these cases (d(1) = [Ti(H2O)6](3+), d(2) = [V(H2O)6](3+), and d(4) = [Mn(H2O)6](3+)), ligand-to-metal charge transfer is prevented to go into those metal orbitals that contain unpaired d electrons. A lowering of the complex symmetry is observed and coupled with the following variations: The Ti(3+)- and V(3+)-hexaaqua ions switch from T(h)() to C(i)() symmetry while the Mn(3+)-hexaaqua ion moves to D(2)(h)() symmetry. The loss of orbital overlap leading to a diminished ligand-to-metal charge transfer toward the single occupied metal orbitals is compensated by amplified bonding interactions of the ligand orbitals with the unoccupied metal orbitals to some extent.

Structure and Dynamics of the Cd2+ Ion in Aqueous Solution: Ab Initio QM/MM Molecular Dynamics Simulation.

“…The six coordination number was observed with the water exchange between the first hydration shell and the bulk ((s M ) 258C 5 6.0 3 10 24 ). 9 Using the B3LYP/6-311G*(5d,7f) level of theory, 10 the C i symmetrical arrangement represents potential energy minima for V 31 aqua ion. 8 These observations are in contrast to T h symmetry with the average V 31 -O bond distance of 2.063 Å predicted by ab initio SCF calculation.…”

“…3,4 Because of the complexity of the V 31 ion in aqueous solution, it has been an interesting area for both experimental and theoretical studies. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] In solution the hexahydrated V 31 is easily oxidized. 19 The oxygen-17 and proton magnetic resonance absorption were employed to investigate the coordination number and the water exchange processes in the hydration shell of vanadium(III) ion in aqueous solution.…”

“…8 These observations are in contrast to T h symmetry with the average V 31 -O bond distance of 2.063 Å predicted by ab initio SCF calculation. 9 Using the B3LYP/6-311G*(5d,7f) level of theory, 10 the C i symmetrical arrangement represents potential energy minima for V 31 aqua ion. Several spectroscopic techniques [11][12][13][14][15][16]20 were applied to evaluate the hydration structure and spectroscopic data of the V 31 ion in b-alums and salts.…”

Dehydrogenation Free Energy of Co2+(aq) from Density Functional Theory-Based Molecular Dynamics

“…24,86 More precisely, the valence band maximum of water is placed at a too high position and (due to hybridization of the solute levels with the band states) the ionization potential of the solute is underestimated. 24,30,85 This effect is most pronounced in species with high, positive redox potentials, and levels close to the valence band maximum of the solvent, but does not strongly depend on hydrogen-bonding, or other structural features. 24,85 Furthermore, misalignment of the water bands leads to a spurious deviation from the linear response regime that could also be mitigated with hybrid functionals.…”

Origins of contrasting copper coordination geometries in crystalline copper sulfate pentahydrate

“…[31][32][33][34] Yet these aspects are of critical importance in determining the various physical properties of a material, such as molecular structure, electronic absorption and emission profiles, and catalytic potential. [35][36][37][38][39] Solid-state DFT has proven to be a powerful tool for the study of crystals containing transition metals, and enables direct investigation of these fundamental interactions. 40,41 The utilization of periodic boundary conditions in solid-state DFT permits the simulation of observable properties with greater accuracy as compared to isolated cluster calculations (when using the same level of theory), allowing for even subtle bulk effects to be captured.…”