Deciphering the bonding mode of the trihalide ligands in a series of halogen carrier homo- and hetero-trihalide Cu(II) Schiff base complexes
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Tsipis, A. C.
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Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
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Tsipis, A. C.
(EN)
Electronic structure calculation techniques (DFT) have been used to decipher the bonding of the trihalide ligands in a series of homo- and hetero-trihalide Cu(II) Schiff base complexes formulated as [Cu(RdienR)(X)(XY2)] (RdienR = Schiff base; R = furan, thiophene or pyrrol; X = Cl or Br; Y = Cl, Br or I). The association of the incoming Y-2 halogen molecule with one of the halide X ligands of the precursor [Cu(RdienR)(X)21 complexes alters their distorted trigonal bipyramidal stereochemistry which is transformed to a distorted square pyramidal geometry. The bonding mechanism between the halogen Y2 molecule and the halide X ligand was thoroughly explored by means of various electronic parameters and charge decomposition analysis techniques. The bond dissociation energy of the Cu-XY2 bond, BDECu-XY2, was estimated in the range of 61.9-68.4 kcal/mol, while the bond dissociation energy of the X-Y-2 bond, BDECu-XY2, was found in the range of 10.6-12.5 kcal/mol. It was found that the X...Y-2 interactions correspond to weak hyperconjugative donor-acceptor interactions between a non-bonding n(X) molecular orbital (donor orbital) localized on the coordinated halide X ligand and an antibonding sigma*(Y-Y) molecular orbital (acceptor orbital) localized on the Y-2 halogen molecule. The n(X) -> sigma*(Y-Y) donor-acceptor interactions are associated with a second-order perturbation stabilization energy, Delta E(2) of 34.5-52.5 kcal/mol. The loose association of the halogen molecules with the coordinated halide ligand renders the [Cu(RdienR)(X)(XY2)1 complexes good halogen carrier molecules. (C) 2007 Elsevier Ltd. All rights reserved.
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