Change in electronic structure in a six-coordinate copper(II) complex accompanied by an anion order/disorder
Colin A Kilner1, Malcolm A Halcrow
1Department of Chemistry, University of Leeds, Leeds LS2 9IT, England.
Abstract:
A variable-temperature crystallographic study of [Cu(L(OH))(2)][ClO(4)](2).2(CH(3))(2)CO [L(OH) = 2,6-bis(hydroxyiminomethyl)pyridine] between 30 and 300 K is presented. The complex exhibits an unusual electronic structure at room temperature with a {d(z(2))}(1) ground state, corresponding to an axially compressed ligand coordination geometry about the copper ion. This reflects a suppression of the pseudo-Jahn-Teller distortion that is normally shown by copper(II) compounds with this ligand geometry [Halcrow et al. (2004). New J. Chem. 28, 228-233]. On cooling the compound undergoes an abrupt structural change at 157 +/- 3 K, that does not involve a change in the space group (P1), but causes significant changes to c and the unit-cell angles. This reflects a conformational rearrangement of the complex dication, towards a more typical pseudo-Jahn-Teller elongated coordination geometry. This occurs concurrently with a crystallographic ordering of one of the two perchlorate anions, and a significant displacement of the two lattice acetone molecules. The transformation involves displacements of up to 0.5 A in the non-H atoms of the structure at 30 K, compared with their positions at 300 K. The change in coordination geometry of the complex around 157 K is reflected in a small reduction in its magnetic moment near that temperature.
More Related Videos
Related Concept Videos
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:42Valence Bond Theory
02:57Coordination Number and Geometry
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:34Structural Isomerism
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...