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

Abstract

Unlike their octahedral analogues, copper(II) compounds with trigonal prismatic stereochemistry undergo an elongation of two bonds in cis positions due to a Jahn-Teller effect, a behavior that can also occur in slightly twisted octahedra.

The Trigonal Prism in Coordination Chemistry

“…Such a distortion corresponds to an E' mode (see Scheme 2 and Table 1), which induces the simultaneous elongation of two cis and shortening of the other four bonds or vice versa, [85] with a possible additional SOJT distortion of the resulting C 2v complex that implies the asymmetrization of the two long metal-ligand bonds. [28] In our preliminary communication we provided evidence for the presence of the cis Jahn-Teller distortion in a variety of Cu II compounds, including minerals and metalloenzymes. As an example, we show in Figure 12 the coordination polyhedron of copper in Sr 3 CuRhO 6 .…”

“…[90] For intermediate geometries along the Bailar interconversion path (D 3 point group), both the cis and trans distortions are Jahn-Teller active, as theoretically predicted and confirmed by structural data for Cu II compounds. [28] One should expect the same distortions to be present in high-spin complexes of d 4 ions such as Mn III or Cr II . Since all Cr II centers in the CSD have been found to be nearly octahedral (octahedral shape measures smaller than 2.0), we search for the bond-stretch distortion among the Mn III compounds.…”

“…e) An interesting example of the influence of the electron configuration on the stereochemical choice is found in a compound that bears one Mn II and one Mn IV center with ligand 4 c. While the former is trigonal prismatic, the latter presents a nearly octahedral coordination. [89] Bond-stretch distortions: In a recent communication, [28] we have shown that the (a' 1 ) 2 A C H T U N G T R E N N U N G (2e') 4 (e") 3 electron configuration of a trigonal-prismatic copper(II) complex is susceptible to a first-order Jahn-Teller distortion associated to the inhomogeneous occupation of e''. Such a distortion corresponds to an E' mode (see Scheme 2 and Table 1), which induces the simultaneous elongation of two cis and shortening of the other four bonds or vice versa, [85] with a possible additional SOJT distortion of the resulting C 2v complex that implies the asymmetrization of the two long metal-ligand bonds.…”

“…It was further shown that for copper(II) coordination spheres intermediate between the octahedron and the trigonal prism both cis and trans distortions can be observed. [28] In that work, a qualitative molecular orbital analysis suggested that such a Jahn-Teller distortion should also be present in d 4 metal ions surrounded by a trigonal-prismatic set of donor atoms.…”

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…In the following, we focus on the effects of the coordination features on magnetic anisotropy in mononuclear hexacoordinated complexes. Qualitative d orbital splitting diagrams for a hexa-coordinated complex with regular octahedral (O h ) [127][128][129], tetragonal elongated [127][128][129], and trigonal prism (D 3h ) [130] geometries are shown in Scheme 6. Scheme 6.…”