The mixed-valence sesquioxides A4O6 (A = alkali metal) are particularly intriguing magneticmaterials comprising of non-magnetic (O2)2- and magnetic (O2)- anions. Recent theoretical work has revealed the importance of electron correlations in describing their electronic structure, while magnetisation measurements have unveiled a very complex magnetic phase diagram culminating to a magnetic low-temperature electronic state. With the presentexperiments we will initiate a systematic neutron diffraction study of these systems in an attempt to both characterise the low-temperature crystalline and magnetic state andinvestigate the nature of the structural and maagnetic evolution with temperature.