A Computational Analysis of the Intrinsic Plasticity of Five‐Coordinate Cu(II) Complexes and the Factors Leading to the Breakdown of the Orbital Directing Effect in Paddlewheel Secondary Building Units

Abstract

Quantum chemical calculations on model copper paddlewheel (CPW) complexes of general formula [Cu2(μ2‐O2CR)4L2] establish two local coordination geometries at the metal centers depending on the balance between equatorial and axial ligand fields. When the equatorial field is stronger than the axial field (large ligand field asymmetry), dominates the stereochemical activity of the d9 shell resulting in a relatively rigid, “orbitally directed” planar or square pyramidal structure. However, if the axial field is significantly increased, or the equatorial field moderately weakened, a small ligand field asymmetry results and both and are involved in the stereochemical activity. This results in a “plastic,” distorted trigonal bipyramidal geometry where the former axial ligand moves into one of the original four equatorial positions. Linkers already used to synthesize zinc‐dabco MOFs (dabco = 1,4‐diazabicyclo[2.2.2]octane) are shown to generate plastic CPW secondary building unit analogs with potential implications for conferring breathing behavior for MOFs which would currently be assumed to be rigid. © 2019 Wiley Periodicals, Inc.

London Dispersion Governs the Interaction Mechanism of Small Polar and Nonpolar Molecules in Metal–Organic Frameworks

“…We recently presented the possibility to perform molecular dynamics (MD) simulations of DUT8-(Ni) by employing ligand field molecular mechanics (LFMM) for the description of the metal nodes . Alzahrani and Deeth lately also confirmed the applicability of LFMM for the description of flexibility in MOFs …”

“…25 Alzahrani and Deeth lately also confirmed the applicability of LFMM for the description of flexibility in MOFs. 29 Experimental adsorption energies of chlorinated methanes (CH x Cl 4-x , x = 0 to 3) in DUT-8(Ni) (−25 to −40 , −35 to −50 , −30 to −40 and −20 to −40 kJ mol −1 for CCl 4 to CH 3 Cl respectively, see Figure 2b) 26,30 suggest, in agreement with chemical intuition, a significant impact of the guest's dipole moment on the adsorption energy. From the experimental data, a trend relating the adsorption energies with the electrostatic interactions could be suspected (see Figure 2a), even though the reported energy ranges are large.…”

“…25 Alzahrani and Deeth lately also confirmed the applicability of LFMM for the description of flexibility in MOFs. 29 From the experimental adsorption energies of chlorinated methanes (CH x Cl 4−x , x = 0−3) in DUT-8(Ni) (−25 to −40, −35 to −50, −30 to −40, and −20 to −40 kJ mol −1 for CCl 4 to CH 3 Cl respectively, see Figure 2b), 26,30 a significant influence of the guest's dipole moments (i.e., the electrostatic interactions) is anticipated because of the high adsorption energy of CH 3 Cl (see Figure 2a), even though the reported energy ranges are large. Herein, we investigate the contributions of electrostatic and London dispersion interactions upon the adsorption energies of chlorinated methanes (CH x Cl 4−x , x = 0−4) in DUT-8(Ni) by using LFMM simulations.…”

Ab Initio Study of Hydrostable Metal–Organic Frameworks for Postsynthetic Modification and Tuning toward Practical Applications

“…During the optimization, Cu–Cu and the gas molecule were free to move, while the remaining structure was constrained. This allows for the structural transformations that occur during adsorption, − while minimizing computational cost. The geometry optimization strategy was validated by comparing a fully optimized MOF–gas complex without restrictions (CO, CO 2 , and H 2 O) to the partially optimized structure, where only the Cu atoms and gas molecules were free to move.…”

London Dispersion Governs the Interaction Mechanism of Small Polar and Non-Polar Molecules in Metal-Organic Frameworks

“…25 Alzahrani and Deeth lately also confirmed the applicability of LFMM for the description of flexibility in MOFs. 29 Experimental adsorption energies of chlorinated methanes (CH x Cl 4-x , x = 0 to 3) in DUT-8(Ni) (−25 to −40 , −35 to −50 , −30 to −40 and −20 to −40 kJ mol −1 for CCl 4 to CH 3 Cl respectively, see Figure 2b) 26,30 suggest, in agreement with chemical intuition, a significant impact of the guest's dipole moment on the adsorption energy. From the experimental data, a trend relating the adsorption energies with the electrostatic interactions could be suspected (see Figure 2a), even though the reported energy ranges are large.…”