The square-planar to flattened-tetrahedral CuX4(2-) (X = Cl, Br) structural phase transition in 1,2,6-trimethylpyridinium salts.

Abstract

The abrupt green-to-yellow thermochromism observed for certain A2CuCl4 compounds has long been attributed to the presence of strong N-H hydrogen bonding in the low-temperature phase that favors square-planar CuCl4(2-) (green in color) through reduction of ligand-ligand repulsion. Weakening of the hydrogen bonding at higher temperature results in the transformation to (far more common) flattened-tetrahedral geometry - the expected geometry for CuBr4(2-) complexes due to their greater ligand-ligand repulsion. The square-planar to flattened-tetrahedral transitions in (1,2,6-trimethylpyridinium)2CuX4 provide the first examples of this phase transformation in the absence of N-H hydrogen bonding and for a CuBr4(2-) complex. These results suggest that the square-planar to flattened-tetrahedral transformation in CuX4(2-) systems may be more common than previously thought.

DOI: 10.1107/S205252061402664X

Cite this paper

@article{Kelley2015TheST, title={The square-planar to flattened-tetrahedral CuX4(2-) (X = Cl, Br) structural phase transition in 1,2,6-trimethylpyridinium salts.}, author={Annette F Kelley and Sowjanya Nalla and Marcus R. Bond}, journal={Acta crystallographica Section B, Structural science, crystal engineering and materials}, year={2015}, volume={71 Pt 1}, pages={48-60} }