A survey of the crystal structures containing simple {M4O4} cubane units is reported. It shows that the average M–M distance in these complexes is relatively constant for a given metal ion M. The structures are all distorted from the idealised cube to a Td structure, and most show a further distortion which, however, usually maintains some elements of symmetry. A system for classifying the different types of ligand in these complexes is proposed. Two new cubanes of cobalt(II) and nickel(II) with the ligand (R,R)-bis-1,2-(1-methylbenzimidazol-2-yl)ethane-1,2-diol, (R,R)-1 or its enantiomer have been isolated and the crystal structure of the cobalt(II) complex confirms the cubane structure. Electronic, CD and 1H NMR spectra and magnetic susceptibility data are reported. The magnetic data for these and other compounds in the literature are discussed in terms of the structural parameters.