[Pd(MeCN) 4 ] 2+ •MeCN complex in the gas phase The transition state (TS) structure corresponding to pentacoordinated trigonal bipyramid was obtained at the TPSS0-D3BJ/def2-TZVP level of theory (Fig. ) and was used as a starting point for a 2D relaxed PES scan along the two Pd-N bonds involved in the ligand exchange. These bonds are of equal length in the TS (2.28 Å); while the length of the remaining three Pd-N bonds is equal to 1.95 Å. The PES scan resulted in a total of 25 structures (5x5 grid). In the following paragraphs, TS refers to the transition state structure of [Pd(MeCN) 4 ] 2+ •MeCN obtained from the PES scan mentioned above, while reactant state (RS) refers to the structure obtained from the geometry optimization of TS in gas-phase with TPSS0-D3BJ/def2-TZVP.