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 |
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Authors: | Khalid A H Alzahrani Robert J Deeth |
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Institution: | 1. Department of Chemistry, King Abdulaziz University, Jeddah, 21589 Saudi Arabia;2. Inorganic Computational Chemistry Group, Department of Chemistry, University of Warwick, Coventry, CV4 7AL United Kingdom |
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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-diazabicyclo2.2.2]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. |
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Keywords: | copper paddlewheel flexible MOFs orbital directing effect quantum chemical calculations |
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