Abstract
Meridional (mer) coordination promotes the generation of larger and lower-symmetry prismatic metallosupramolecular structures, in contrast with the facial (fac) coordination common to smaller and higher-symmetry polyhedra. Here, we describe a general route to the selective formation of large metallosupramolecular prisms that contain exclusively mer-coordinated metal vertices. The use of 2-formylpyridine subcomponents that contain perfluorophenylene substituents at their 5-positions resulted in stereoselective formation of the iron(II) complexes from these subcomponents. Only mer vertices were observed, as opposed to the statistical fac/mer mixture otherwise generated. This mer-selective self-assembly could be used to prepare tetragonal (M8L12), pentagonal (M10L15), and hexagonal (M12L18) prisms by taking advantage of the subtle selectivities imposed by the different anilines and counterions employed. The equilibrium between the tetragonal and pentagonal prism followed a linear free-energy relationship, with the ratio between structures correlating with the Hammett σp(+) parameter of the incorporated aniline. The contrasting preferences of the fluorinated and nonfluorinated ligands to generate prisms and tetrahedra, respectively, were quantified energetically, with the destabilization increasing linearly for each "incorrect ligand" incorporated into either structure.
Highlights
Recent advances in supramolecular chemistry have produced a host of intricate self-assembled architectures of increasing structural[1] and functional complexity.[2]
We postulated that by making the aromatic substituent at the 5-position on the pyridine rings more sterically demanding, the formation of fac vertices might be disfavored relative to mer, as illustrated in the van der Waals space-filling models and surfaces provided in Supporting Information (SI) section S2.1
This achiral structure contrasts with the chiral pentagonal prisms observed previously that contained metal centers of only one handedness in all cases.4c,20 Similar to the structure of 4a, PF6− counterions are found in partially enclosed pockets within the top and bottom pentagonal rings (Figure 6c); several of the anions were disordered or modeled with partial occupancy
Summary
Recent advances in supramolecular chemistry have produced a host of intricate self-assembled architectures of increasing structural[1] and functional complexity.[2]. This achiral structure contrasts with the chiral pentagonal prisms observed previously that contained metal centers of only one handedness in all cases.4c,20 Similar to the structure of 4a, PF6− counterions are found in partially enclosed pockets within the top and bottom pentagonal rings (Figure 6c); several of the anions were disordered or modeled with partial occupancy. Anilines bearing substituents with varying electronic effects were combined with subcomponent D and Fe(PF6)[2] This iron(II) salt was chosen because ESI-MS and 1H NMR indicated that it led to the formation of a mixture of two structures only (4 and 5) (Figure 8). The strength of the metal−ligand interaction, as influenced by the substituents of the aniline residues, impacts strongly upon the equilibrium between these prismatic structures
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