Topological Control in Heterometallic Metal−Organic Frameworks by Anion Templating and Metalloligand Design

Abstract

Several new heterometallic metal-organic frameworks (MOFs) based on tris(dipyrrinato) metalloligands and Ag+ salts are reported. MOFs were prepared systematically to examine the effects of the core metal ion, counteranion, and ligand structure on the topology of the resultant network. The effect of the metal ion (Fe3+ vs Co3+) on MOF structure was generally found to be negligible, thereby permitting the facile synthesis of trimetallic Fe/Co/Ag networks. The choice of anion (e.g., silver salt) was found to have a pronounced effect on the MOF topology. Networks prepared with salts of AgO3SCF3 and AgBF4 reliably formed three-dimensional (10,3) nets, whereas use of AgPF6 and AgSbF6 produced two-dimensional (6,3) honeycomb nets. The topology generated upon formation of the MOF was found to be robust in certain cases, as demonstrated by anion-exchange experiments. Anion exchange was confirmed by X-ray crystallography in a rare set of apparent single-crystal-to-single-crystal transformations. The data presented here strongly suggest that the coordinative ability of the anion does not play a significant role in the observed templating effect. Finally, changes in the length of the tris(dipyrrinato) metalloligand were found to override the anion templating effect, resulting exclusively in two-dimensional (6,3) nets. These studies provide a basis for the rational design of MOF topologies by choice of ligand structure and anion templating effects. Furthermore, the results demonstrate the ability of carefully designed metalloligands to generate MOFs of structure strikingly similar to that of their organic counterparts.

Self‐Assembly and Anion‐Exchange Properties of a Discrete Cage and 3D Coordination Networks Based on Cage Structures

“…It is suggested that the overall structure of the network is strongly influenced by the geometry and the size of the anion, together with its ability to interact with the metal center. [31] The flexible dihedral angles between the pyridine and triazole rings also provide the curva- Anion-exchange properties and the transformation from discrete cage to 3D coordination network: We explored the anion-exchange reactions of these cage-like architectures. After gently stirring 1 (0.5 mmol) in a 2:1 H 2 O/CH 3 CN solution containing 5 mmol NaClO 4 for about 6 h the resultant mixture was evaporated at room temperature for two weeks.…”

Construction of Heterometallic Cages with Tripodal Metalloligands

“…[2] Both homoleptic and heteroleptic organic ligands have been used in the preparation of cage complexes. [3] Although metalloligands have been extensively employed in the preparation of functional metal-organic frameworks, [4] fewer examples of discrete polyhedral complexes that involve the use of metalloligands have been reported. [5] Compared with organic ligands, metalloligands may function as bridging ligands with some additional advantages: 1) the introduction of new functionality, such as chirality and spectroscopic character; 2) flexible geometric control, which could avoid complex modification of the organic ligand structure; 3) the ability to assemble many components into a discrete entity.…”

Application of Metal–Organic Frameworks in Fine Chemical Synthesis

“…The development of advanced MOFs employs prefunctionalized moieties such as metalloligands that are introduced before or during the MOF synthesis [69,70]. The incorporation of metallic complexes into the MOF structure can readily be achieved via a direct self-assembly approach (Figure 10.5).…”