The combination of Cu(NO(3))(2), potassium hydrogen saccharate (KC(6)H(9)O(8)) and 1,10-phenanthroline (phen) yields a pair of chiral cluster compounds, each with composition Cu(21)(C(6)H(5)O(8))(6)(phen)(12)(NO(3))(12)center dot solvate. One of the compounds forms as orthorhombic crystals, while the other forms cubic crystals. Each of the clusters has D(3) or approximate D(3) symmetry, but the arrangement of the saccharate ion in the clusters is quite different in the two cases. The clusters in the cubic form interact with neighbouring clusters through face-to-face p interactions involving the phen ligands, an association that leads to the generation of very large solvent-filled spaces in the crystal structure. In contrast the clusters in the orthorhombic form are much more densely packed. At the centre of each cluster that crystallises in the orthorhombic form is a nitrate anion that binds to six Cu(II) centres. ESI mass spectral studies indicate that the Cu(21) clusters exist in solution. Solid-state magnetic studies of the cubic form of Cu(21) show that antiferromagnetic coupling occurs to leave a nonzero-spin ground state, and comparisons are made to the magnetic data for other large CuII clusters.