Crystal engineering is the rational design and assembly of solid-state structures with desired properties via the manipulation of intermolecular interactions, hydrogen bonding and metalligand complexation in particular. The heart of crystal engineering is to control the ordering of the building blocks, be they molecular or ionic, toward a specific disposition in the solid state. The relatively weak strength of intermolecular forces with respect to chemical bonding renders the assembly of

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... lecular constructs sensitive to external physical and chemical stimuli, with pH condition of the reaction mixture being arguably the most prominent and extensively observed. Using selected examples of constructing metal-organic architectures from recent literature, the influences of pH on the specific ligand forms, the generation and metal coordination of hydroxo ligands, ligand transformation promoted by pH condition changes, pH-dependent kinetics of crystallization of a number of metal-organic architectures are discussed. Current status of this particular areas of research in supramolecular chemistry and materials are assessed and personal perspectives as to toward what directions should this chemistry head are elaborated. La-Sheng Long received his B.S. and M.S. degrees in chemistry respectively from Anhui Normal University in 1986 and Lanzhou University in 1989, and his Ph.D. from Zhongshan University in 1999. He is now a professor of Xiamen University. His current research is focused on the synthetic and materials chemistry of cluster compounds of lanthanide-transition metal elements.