Dynamic processes in crystals examined through difference displacement parameters .DELTA.U: pseudo-Jahn-Teller distortion in cis-Cu(II)N4O2 coordination octahedra

Jahn–Teller distortions of six-coordinate CuII compounds: cis or trans?

“…Remarkably, there are compounds with two crystallographically independent molecules presenting cis and trans distortions, respectively. 18,34 Although these data should be taken with care, given the possibility of a dynamic Jahn-Teller effect or static disorder, 6,9,35 they are consistent with our computational results and seem to provide a good starting point for more accurate crystallographic studies.…”

The geometry of metal–ligand interactions relevant to proteins

“…For Cu, this intermediate geometry seen is easily understood on the basis of the Jahn±Teller effect; the primary bond, MÐO2, is a short bond within the square-planar base, 1.91±2.03 A Ê , and the secondary bond, MÐO1, is to oxygen in a near axial position and is usually 2.2±2.6 A Ê . Even some of those which appear to be symmetrical bidentate may be unsymmetrical and disordered (Stebler & Burgi, 1987;Simmons et al, 1987). Zinc is different.…”

Synthesis and structural characterisation of the isotypic complexes MIIL2(py)2·2H2O (M = Cu, Zn); the interplay of lattice imposed ligand disposition and Jahn–Teller distortions [HL = 5-(4-methoxyphenyl)pyrazole-3-carboxylic acid] †

“…In contrast to the zinc centres in 5, the coordination geometries of the two unique copper centres in 6 are significantly different, with each copper demonstrating a different apparent distortion: Cu(1) has a small elongation along the Cu-N(py) axis whereas Cu(2) has a pronounced elongation along the Cu-O axis. In both cases the Cu-N(pz) bond is the shortest at 1.978 (7) (2). For the Cu(1) site a clear cut tetragonal distortion is not evident.…”

“…However, the presence of static/dynamic disorder of two or more structures can be identified by comparing the components of the anisotropic displacement parameters (U ) for the copper atom and the ligand donor atom along the M-X bond. 7 The nature of the pseudo-Jahn-Teller distortion in transdiaquabis(methoxyacetato)copper() has been recently reported at a selection of temperatures over the range 4.2-325 K. 8 The apparent tetragonal compression (short Cu-carboxylate distance) at room temperature is described as a planar dynamic Jahn-Teller system which upon cooling converts to a static tetragonal elongation (long Cu-methoxy distance). In this case the corresponding nickel() complex is isostructural and at room temperature has a nearly regular octahedral coordination, whereas the zinc() complex adopts the alternative cisdiaqua structure.…”