Abstract
A self-assembled coordination cage usually possesses one well-defined three-dimensional (3D) cavity whereas infinite number of 3D-cavities are crafted in a designer metal-organic framework. Construction of a discrete coordination cage possessing multiple number of 3D-cavities is a challenging task. Here we report the peripheral decoration of a trinuclear [Pd3L6] core with one, two and three units of a [Pd2L4] entity for the preparation of multi-3D-cavity conjoined-cages of [Pd4(La)2(Lb)4], [Pd5(Lb)4(Lc)2] and [Pd6(Lc)6] formulations, respectively. Formation of the tetranuclear and pentanuclear complexes is attributed to the favorable integrative self-sorting of the participating components. Cage-fusion reactions and ligand-displacement-induced cage-to-cage transformation reactions are carried out using appropriately chosen ligand components and cages prepared in this work. The smaller [Pd2L4] cavity selectively binds one unit of NO3−, F−, Cl− or Br− while the larger [Pd3L6] cavity accommodates up to four DMSO molecules. Designing aspects of our conjoined-cages possess enough potential to inspire construction of exotic molecular architectures.
Highlights
A self-assembled coordination cage usually possesses one well-defined three-dimensional (3D) cavity whereas infinite number of 3D-cavities are crafted in a designer metal-organic framework
Spontaneous assembly of the components resulted in the complex [Pd3(L3)6](NO3)6, 3a within 10 min at room temperature (Fig. 3c) and the 1H nuclear magnetic resonance (NMR) spectrum of the solution (Fig. 4b) showed a single set of signals where a downfield shift was seen in the positions of the pyridineα protons
The bidentate ligand L3 possesses a central aromatic spacer and two terminal 3-pyridyl moieties connected by ester linkages
Summary
Spontaneous assembly of the components resulted in the complex [Pd3(L3)6](NO3)6, 3a within 10 min at room temperature (Fig. 3c) and the 1H NMR spectrum of the solution (Fig. 4b) showed a single set of signals where a downfield shift was seen in the positions of the pyridineα protons. Complexation of Pd(NO3)[2] (4 equiv.) with a mixture of the ligands L3 (2 equiv.) and L5 (4 equiv.) was carried out in DMSO-d6 Integrative selfsorting of these components required 4 h at room temperature or 1 h at 70 °C, as revealed by monitoring of 1H NMR spectra, yielding [NO3 ⊂ Pd4(L3)2(L5)4](NO3)7, 4a (Fig. 3f). While the 1H NMR spectra recorded at different temperatures (30 to 100 °C range)
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