A discrete neutral transition-metal citrate cubane with an M4O4 core; coordinative versatility of the [M-4(II)(citrate)(4)](8-) fragment.

The neutral cluster [Mn-8(II)(citrate)(4)(H2O)(18)] is formed by the [M-4(citrate)(4)](8-) fragment, with an Mn4O4 cubane core, which bonds four peripheral aquomanganese units – two [Mn(H2O)(4)](2+) and two [Mn(H2O)(5)](2+) – through a total of six metal-ligand bonds, giving a discrete neutral compound. The compound presents a unique coordination mode in which the citrate cubane acts as a chelate to each of the two peripheral [Mn(H2O)(4)](2+) (tetra-aquo) units. A detailed analysis of the central and peripheral geometries is given in terms of the tetrahedral distortions of key structural features. A reversible dehydration-rehydration process has been observed in a polycrystalline sample of the complex, whose structure lacks pores or channels.