The mixed-valence sesquioxides A4O6 (A = alkali metal) are particularly intriguing molecular materials comprising of non-magnetic (O2)2- and magnetic (O2)- anions. Our recent diffraction work at ISIS has unveiled a very complex structural phase diagram at ambient pressure also characterised by extreme sensitivity to thermal protocols and thermal history of the sample. With the present experiments we will extend our investigations to high pressure and initiate a systematic neutron diffraction study of these systems at elevated pressures in an attempt to investigate the nature of the structural evolution with pressure and compare the structural (andelectronic/magnetic) response with that at ambient pressure.