Morphological and structural effects of gels on coordination polymers crystallization

The use of gels or viscous materials as growth media for a wide range of compounds, including proteins and inorganic and organic compounds has been reported in the literature. In the presence of gel, sedimentation and convection currents are greatly suppressed and the mass transport of the molecules mainly occurs by diffusion, resulting, usually, in a lower nucleation density and a better crystal quality.[1a] Here we report some new interesting phenomena observed in crystallization experiments of coordination compounds, such as, “coordination polymers”, by using gels as diffusion media.[1b] By using a semi-liquid silica-gel system as a dispersion matrix, we were able to increase the quality of the crystals but also slow down the solvent loss, stabilizing the partially dehydrated structure of a very flexible porous framework. This has enabled an accurate determination of the dynamic behavior of the system during the desolvation process by using single crystal X-ray diffraction. Unit cells and structure solution has been obtained at any point during the process. The improved stability of the crystals and the large flexibility of the network have also made possible to carry out in-situ high-pressure diffraction measurements. Other important results concern the effects of gels on the macroscopic crystal shape and on the micromorphology of the crystal surfaces (Figure), and the capacity of gel media to promote the concomitant crystallization of topological isomers with a monotropic relationship.[2] Funding from the Cariplo Foundation under the grant ‘‘2012‐0921” is gratefully acknowledged. [1] a) K.H. Henisch, Crystals in Gels and Liesegang Rings, Cambridge University Press, Cambridge, 1998; b) L. Carlucci, G. Ciani, J. M. Garcìa-Ruiz, M. Moret, D. M. Proserpio and S. Rizzato Cryst. Growth Des., 2009, 9(12), 5024-5034. [2] S.Rizzato et al., unpublished results.