The geometry of the [CuCl5]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 D3h and at <280 K as an elongated pyramid with symmetry C2v. Three routes for D3h-C2v 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). The three paths are governed by the TBP’s totally symmetric 2alpha1’ and degenerate 3epsilon’ vibrational modes taken in different combinations. The global energy minimum as a function of the TBP vibrational coordinates occurs for the C2v symmetry. The compressed TBP structure (D3h) is a local minimum readily accessible from the C2v structure at >280 K. Route 3 with fixed axial bonds dominates the interconversion process. The two totally symmetric modes alpha1’ play a very important role in this process since they compress the TBP and facilitate the equatorial bond changes.