Water exchange rates and mechanisms in tetrahedral [Be(H₂O)₄]²⁺ and [Li(H₂O)₄]⁺ complexes using DFT methods and cluster‐continuum models

Abstract

The water exchange reactions in aquated Li 1 and Be 21 ions were investigated with density functional theory calculations performed using the [Li(H 2 O) 4 ] 1 Á14H 2 O and [Be(H 2 O) 4 ] 21 Á8H 2 O systems and a cluster-continuum approach. A range of commonly used functionals predict water exchange rates several orders of magnitude lower than the experimental ones. This effect is attributed to the overstabilization of coordination number four by these functionals with respect to the five-coordinated transition states responsible for the associative (A) or associative interchange (I a ) water exchange mechanisms. However, the M06 and M062X functionals provide results in good agreement with the experimental data: M062X/TZVP calculations yield a concerted I a mechanism for the water exchange in [Be(H 2 O) 4 ] 21 Á8H 2 O that gives an average residence time of water molecules in the first coordination sphere of 260 ls. For [Li(H 2 O) 4 ] 1 Á14H 2 O the water exchange reaction is predicted to follow an A mechanism with a residence time of inner-sphere water molecules of 25 ps. K E Y W O R D S berylium, density functional calculations, lithium, water exchange

A Phosphine Oxide-Functionalized Cyclam as a Specific Copper(II) Chelator

“…For the aquo complexes, we performed calculations on the [M­(H 2 O) 6 ] 2+ ·12H 2 O systems, which incorporate 12 explicit second-sphere water molecules (Tables S8–S11 and Figure S26). , This allowed us to overcome the known convergence problems faced when optimizing the [M­(H 2 O) 6 ] 2+ systems using polarized continuum models . Our DFT calculations afford Δ G ° values of −76, −52, and −46 kJ mol –1 for M = Co, Ni, and Zn, respectively.…”

“…Solvent effects were incorporated using a polarized continuum model with the default parameters implemented in Gaussian [scrf = (pcm, solvent = water)]. The structures of the [M­(H 2 O) 6 ] 2+ ·12H 2 O systems were optimized using input structures from previous computational studies …”

“…50,51 This allowed us to overcome the known convergence problems faced when optimizing the [M-(H 2 O) 6 ] 2+ systems using polarized continuum models. 52 Our DFT calculations afford ΔG°values of −76, −52, and −46 kJ mol −1 for M = Co, Ni, and Zn, respectively. This is in line with the Irving−Williams order, which predicts the following trend in complex stability: Co 2+ < Ni 2+ < Cu 2+ > Zn 2+ .…”

“…The structures of the [M(H 2 O) 6 ] 2+ •12H 2 O systems were optimized using input structures from previous computational studies. 52 The 63 Cu hyperfine coupling tensors and g tensors were calculated with the ORCA program package (version 5.0.3). 62,63 Hyperfine coupling constants were obtained using DFT with the TPSSh functional 64 and the Def2-QZVPP 60 basis set.…”

Benchmarking of DFT methods using experimental free energies and volumes of activation for the cycloaddition of alkynes to cuboidal Mo3S4 clusters

“…Here, we have instead computed Δ V ‡ values based on the differences between the vdW volumes of transition state structures and reactants, a methodology successfully used, for instance, to study water exchange processes at transition metal complexes. [ 66,67 ]…”