Correlation between DFT calculated and X-ray structures from CSD,for Cu(II) and Cu(I) coordination spheres when coordinated to four acyclic amine ligands. A reconsideration of copper(II) planarity |
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Authors: | Francesco Caruso Miriam Rossi Alessio Caruso |
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Institution: | 1. Department of Chemistry, Vassar College, Poughkeepsie, NY, USACaruso@vassar.edu;3. Department of Chemistry, Vassar College, Poughkeepsie, NY, USA |
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Abstract: | The Cambridge Crystallographic Database (CSD) shows CuIIL4]2+ complexes, L = acyclic amine, fitting well with theoretically calculated structures to describe a planar-to-flat tetrahedral transformation pathway. Statistically, the CuII “planar” coordination sphere shows two distinct sets of trans N–Cu–N bond angles, 180° and near 150°, with the latter somewhat energetically favored according to DFT results. The planar structure is not confirmed theoretically when an example of these molecules in the CSD is geometrically minimized, suggesting that crystallographic or packing forces help to generate the planar structure in the crystal. Results of energy calculations from DFT seem to explain this feature. Less planar and more tetrahedral examples in the CSD are also found and compare well with theoretically converged related molecules. Trans N–Cu–N bond angles near 130° seem feasible for both CuI and CuII coordination spheres. These copper complexes having the copper coordination sphere in a less tetrahedral geometry are suggested as potential alternative models for blue proteins, and they deserve further exploration. |
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Keywords: | Tetrahedral planar configuration DFT Crystal structure Blue protein Packing forces |
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