Selective crystallization between CuSO4·5H2O and Na2SO4·7H2O under a monolayer

Abstract

Two selections have been found to occur in the crystal growth induced by a monolayer of 9-(hexadecylimino)-4,5-diazafluorene. Between CuSO₄·5H₂O and Na₂SO₄·7H₂O, although both were supersaturated, only the former was chosen to nucleate under the monolayer and the latter formed at the bottom of the container. Furthermore, among all of the crystal faces of CuSO₄·5H₂O, the (010) face was selected by the monolayer and the crystallization was oriented. In these processes, the monolayer plays a very important role and acts as a template which can recognize a certain crystal and a certain crystal face. This is due to specific molecular interactions between ions and the hydrophilic head groups of the monolayer, and the influence of some factors including ion binding, lattice matching and structural complementarity. Using the principles of hard–soft acid–base theory, coordination theory and by computer simulation, it was found that the dimensions of the (010) face of CuSO₄·5H₂O match those of the monolayer very well.