Highly versatile metal-organic frameworks

Control over size and shape of nano-micro objects is a pivotal point in modern colloid chemistry both for the investigation of fundamental aspects and for the material design. The synthetic tools to achieve such a control are... [ view full abstract ]

Control over size and shape of nano-micro objects is a pivotal point in modern colloid chemistry both for the investigation of fundamental aspects and for the material design. The synthetic tools to achieve such a control are well established for different classes of inorganic and organic materials and they have led to the enlargement of material properties and applications. However size and shape control is still largely unexplored in the field of metal organic frameworks (MOFs) where hitherto major efforts aimed at the design of the crystallographic structure. In general MOFs produced by free modulator synthesis exhibit a non-homogeneous shape or simple polyhedral morphologies, usually reflecting the underlying geometry of the crystallographic structure. In our work we report on a straightforward, bottom-up approach that results in a tremendous variability of MOF morphologies as consequence of small parameter variation involving just the building blocks. No external templates or modulators are introduced. The set of MOFs that was obtained included rare polyhedral shapes, hollow structures and unique morphologies not classifiable according to the conventional rules for crystalline habit description. Moreover, we show that such shaping ability, beyond the MOF field interests, can also be exploited to address the fundamental question about the relationship between chiralities among different size hierarchies. In particular we prepared a MOF-based system in which the chirality of the crystal structure and morphology were coupled with an unprecedented level of complexity. Unlike most of the examples of organic and inorganic systems used for such studies, in our case at both hierarchies the chirality was not induced by chiral properties of the building blocks or by external chiral agents, strongly suggesting a direct mutual influence between the two levels. The high versatility and the degree of controlling the shaping process proved in this work, suggest new scenario for MOFs, commending them not just as molecular frameworks but also as 3D objects for fundamental studies and nanotechnological applications.