Extended X-ray absorption fine structure, crystal structures at 295 and 173 K, and electron paramagnetic resonance and electronic spectra of bis[tris(2-pyridyl)-methane]copper(II) dinitrate

Astley, Timothy, Ellis, Paul J., Freeman, Hans C., Hitchman, Michael A., Keene, F. Richard, and Tiekink, Edward R.T. (1995) Extended X-ray absorption fine structure, crystal structures at 295 and 173 K, and electron paramagnetic resonance and electronic spectra of bis[tris(2-pyridyl)-methane]copper(II) dinitrate. Dalton Transactions (4). pp. 595-601.

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Abstract

The crystal structure of bis[tris(2-pyridyl)methane]copper(II) dinitrate, [Cu{(C₅H₄N)₃CH}₂][NO₃]₂ has been determined. At 295 K the Cu atom lies on a special position so that all six Cu–N bonds are crystallographically equivalent [Cu–N 2.103(4)Å]. The structure at 173 K is very similar [Cu–N 2.095(3)Å]. However, the electronic spectrum suggests that the Cu²⁺ ion experiences a ligand field of tetragonal symmetry. This has been confirmed by the EXAFS of the compound, which shows four nitrogen atoms at 2.04 Å and two at 2.25 Å from the copper. The apparent trigonal symmetry revealed by the X-Ray analysis is thus due to disorder of the long and short Cu–N bonds about the three-fold axis. The EPR spectrum shows an isotropic signal at 295 K, but a signal characteristic of a tetragonally elongated octahedral complex at 150 K. This suggests that the directions of the long and short bonds interchange rapidly on the EPR time-scale at room temperature, but that the complexes become frozen into particular orientations on cooling.

Item ID: 22752
Item Type: Article (Refereed Research - C1)
Keywords: jahn-teller distortions; pyrazole-derived ligands; coordination; chemistry; angular-overlap; complexes; tris(2-pyridyl)phosphine; tris(2-pyridyl)methane; redetermination; copper(II); dependence
ISSN: 1477-9234
Date Deposited: 16 Aug 2012 06:13
FoR Codes: 03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030207 Transition Metal Chemistry @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 100%
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