Geometry of the Pentachlorocuprate(II) Ion

Abstract

The geometry of the [CuCl 5 ] 3- unit was studied by the Extended Huckel Method with distance-dependent off-diagonal elements in an attempt to explain why the unit exists at >280 K as a compressed trigonal bipyramid (TBP) with symmetry D 3h and at <280 K AS AN ELONGATED PYRAMID WITH SYMMETRY C 2υ . Three routes for D 3h -C 2υ interconversion were considered: Berry pseudorotation exchanging the TBP axial and equatorial ligands without (path 1) or with (path 2) equatorial bond stretching, where one bond is pivotal in this process; bending and stretching only in the equatorial plane with the two axial bonds being pivotal (path 3)