Abstract
Metal organic polyhedra (MOPs) such as coordination cages and clusters are increasingly utilized across many fields, but their geometrically selective assembly during synthesis is nontrivial. When ligand coordination along these polyhedral edges is arranged in an unsymmetrical mode or the bridging ligand itself is nonsymmetric, a vast combinatorial space of potential isomers exists complicating formation and isolation. Here we describe two generalizable combinatorial methodologies to explore the geometrical space and enumerate the configurational isomers of MOPs with discrimination of the chiral and achiral structures. The methodology has been applied to the case of the octahedron {Bi6Fe13L12} which has unsymmetrical coordination of a carboxylate ligand (L) along its edges. For these polyhedra, the enumeration methodology revealed 186 distinct isomers, including 74 chiral pairs and 38 achiral. To explore the programming of these, we then used a range of ligands to synthesize several configurational isomers. Our analysis demonstrates that ligand halo-substituents influence isomer symmetry and suggests that more symmetric halo-substituted ligands counterintuitively yield lower symmetry isomers. We performed mass spectrometry studies of these {Bi6Fe13L12} clusters to evaluate their stability and aggregation behavior in solution and the gas phase showing that various isomers have different levels of aggregation in solution.
Highlights
Coordination-driven self-assembly, which relies on specific metal−ligand interactions, is a powerful method to make several distinct classes of supramolecular coordination complexes (SCCs), metal−organic polyhedra (MOPs), and metal−organic frameworks (MOFs).[1−6] This design needs the combination of both “donor” organic bridging ligands with suitable “acceptor” metal ions or discrete metal-oxo cluster corners to yield a variety of architectures.[7−9] By exploiting metal atoms and metal-oxo clusters as nodes and with symmetric bridging ligands as linkers, a range of self-assembled structures, with specific configurations and conformations of SCCs, MOPs, and MOFs have been rationally synthesized.[10]
Using this approach numerous nodes and organic linkers have been investigated in the past, but the use of nonsymmetric bridging ligands yielding unsymmetric polyhedral edges during the self-assembly process is very limited.[11]
To identify and name each of the 186 isomers, we developed a simple code system for the isomers where each of the six vertices of the polyhedron is labeled according to the number of ligands appended
Summary
Coordination-driven self-assembly, which relies on specific metal−ligand interactions, is a powerful method to make several distinct classes of supramolecular coordination complexes (SCCs), metal−organic polyhedra (MOPs), and metal−organic frameworks (MOFs).[1−6] This design needs the combination of both “donor” organic bridging ligands with suitable “acceptor” metal ions or discrete metal-oxo cluster corners to yield a variety of architectures.[7−9] By exploiting metal atoms and metal-oxo clusters as nodes and with symmetric bridging ligands as linkers, a range of self-assembled structures, with specific configurations and conformations of SCCs, MOPs, and MOFs have been rationally synthesized.[10]Using this approach numerous nodes and organic linkers have been investigated in the past, but the use of nonsymmetric bridging ligands (i.e., ambidentate ligands) yielding unsymmetric polyhedral edges during the self-assembly process is very limited.[11]. Coordination-driven self-assembly, which relies on specific metal−ligand interactions, is a powerful method to make several distinct classes of supramolecular coordination complexes (SCCs), metal−organic polyhedra (MOPs), and metal−organic frameworks (MOFs).[1−6] This design needs the combination of both “donor” organic bridging ligands with suitable “acceptor” metal ions or discrete metal-oxo cluster corners to yield a variety of architectures.[7−9] By exploiting metal atoms and metal-oxo clusters as nodes and with symmetric bridging ligands as linkers, a range of self-assembled structures, with specific configurations and conformations of SCCs, MOPs, and MOFs have been rationally synthesized.[10]. It is possible to employ combinatorial methods to enumerate all the configurational isomers of specified components.[12−16] Investigation may provide insights regarding the reactivity, synthetic accessibility, and potential for supramolecular aggregation of each individual isomer
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