The IP vs. VDE competition as a key factor determining the stability of the MgBX5 (XÂ =Â F, Cl) compounds

► The MgBX5 (X = F, Cl) molecules are kinetically and thermodynamically stable species in the gas phase. These molecules should not be susceptible to any fragmentation process, including the intuitively most likely MgBX5 → MgX2 + BX3 reaction. ► The stability of the MgBX5 compounds is caused by the strong electron acceptor properties of the BX4 subunits (i.e., its ability to significantly ionize the MgX fragment). ► The OBX5 species (X = F, Cl) are not thermodynamically stable molecules (the spontaneous fragmentations leading to OX2 and BX3 are predicted). This instability is primarily caused by the high ionization potential of OCl2 molecule and the BX4 subunits inability to overcome it. ► The competition between the IP and VDE values (characterizing the fragments that the MgBX5 and OBX5 species consist of) is proposed to be a key factor determining the stability of these compounds.