Single-crystal to single-crystal transformations in discrete hydrated dimeric copper complexes

The single crystals of discrete hydrated [(OAc)Cu(mu-hep)(2)Cu(OAc)]center dot 2H(2)O (1 center dot 2H(2)O) and [(OAc)Cu(mu-hep)(2)Cu((OPr)-Pr-n)]center dot 2H(2)O (2 center dot 2H(2)O) (the lattice H2O molecules exist as a tetrameric water cluster, hep-H = 2-(2-hydroxyethyl)-pyridine), OAc- = acetate and (OPr-)-Pr-n = n-propionate) undergo single-crystal to single-crystal (SCSC) transformations to the dehydrated 1 and 2, respectively, under the influence of heat. The reverse SCSC processes of 1/2-->1 center dot 2H(2)O/2 center dot 2H(2)O involving the regeneration of the lattice water tetramers take place on exposure of 1/2 to water vapour. However, the blue single crystal of discrete hydrated [((OPr)-Pr-n)Cu(mu-hep)(2)Cu((OPr)-Pr-n)]center dot 2H(2)O (3 center dot 2H(2)O), incorporating the two bulkier OnPr-terminal bidentate ligands, irreversibly converts to the green single crystal of a unique discrete tetrameric [Cu-4(mu(3)hep)(2)(mu-hep)(2)(mu-(OPr)-Pr-n)(2)((OPr)-Pr-n)(2)] (4) with double open cubane core either by heating or by a simple vapour diffusion technique via the breaking and forming of multiple covalent bonds.