Designed post-self-assembly structural and functional modifications of a truncated tetrahedron

Abstract

Post-self-assembly modifications of a discrete metal-organic supramolecular structure have been developed. Such modifications allow the properties of the self-assembled supramolecular species to be changed in a simple and efficient manner (>90% yield). Initiated by the application of chemical stimuli, the post-self-assembly modifications described herein result in three distinct changes to the supramolecular system: an individual building-block component change, an overall structural modification, and a functional evolution of a [6+4] metal-organic supramolecular structure. The three modifications have been carefully examined by a range of characterization methods, including NMR and UV-vis spectroscopy, electrospray ionization mass spectrometry, pulsed field gradient spin echo NMR measurements, electrochemical analysis, and computational simulations.

Figure 1

(a) ³¹P{¹H} NMR spectrum of 3; (b and c) ³¹P{¹H} NMR spectra of component substitution of 3 to 5; (d) ³¹P{¹H} NMR spectrum of self-assembly of 5 by individual molecular components; (e) ¹H NMR spectrum of 5.

Figure 2

Full ESI-MS spectrum of the triflate salt of 5.

Figure 3

³¹P{¹H} (a–d) and ¹H NMR (e–h) spectra for mixtures of 3 upon addition of 0 equiv. (a and e), 0.25 equiv. (b and f), 0.6 equiv. (c and g), 1.0 equiv. (d and h) of tritopic carboxylate ligand 4.

Figure 4

(a) ³¹P{¹H} NMR spectrum of the discrete [6 + 4] metal-organic supramolecule 3; (b and c) ³¹P{¹H} NMR spectra of the structural modification of 3 to 7; (d) ³¹P{¹H} NMR spectrum of 7 formed from its components; (e) ¹H NMR spectrum of the triflate salt of 7.

Figure 5

Full ESI-MS spectrum of the PF₆ salt of 7.

Figure 6

¹H NMR spectra of non-functional scaffold 10 (a) and electrochemically functionalized supramolecule 11 (b).

Figure 7

(a) Cyclic voltametry of modified supramolecular species 11 at different scan rates (25–150 mV/s) at a ~0.3 mm diameter Pt electrode; (b) Steady-state current response of 11 at 20 mV/s at a microsized (~25 µm diameter) Pt disk electrode. Solution: 0.61 mM 11 in acetone containing 0.1 M n-Bu₄NPF₆.

Figure 8

¹H NMR spectrum of coronene (a), the discrete [6 + 4] metal-organic supramolecule 3 (b), mixture of coronene and 3 (c), and the modified supramolecule 13 (d) in acetone-d₆.

Figure 9

UV-Vis spectrum of the discrete [6 + 4] metal-organic supramolecule 3 and the modified supramolecule 13 ([3] = 1.46 mM and [13] = 1.44 mM in acetone) and coronene ([coronene] = 1.46 mM in benzene).

Figure 10

Calculated (top, blue) and experimental (bottom, red) ESI-MS spectra of the PF₆ salt of 13.

Scheme 1

Post-self-assembly modifications of a discrete [6 + 4] metal-organic supramolecule (3) allowing for component substitution (3 + 4), structural modifications (3 + 6 and 3 + 8), and functional evolutions (3 + 10 and 3 + 12).

Scheme 2

Two pathways (a and b) of component substitution on a discrete [6 + 4] two-component supramolecule (3) into a three-component structure (5) in a same shape; (c) self-assembly of 5 by individual molecular components: cis-Pt(PEt₃)₂(OTf)₂ (1), tripyridyl donor 2, and tricarboxylate ligand 4.

Scheme 3

Two different pathways (a and b) for the structural modification of a discrete [6 + 4] metal-organic supramolecule 3 from an truncated tetrahedron into a square pyramid 7; (c) self-assembly of 7 using molecular components: cis-Pt(PEt₃)₂(OTf)₂ 1, tripyridyl donor 2, and dicarboxylate ligand 6.

Scheme 4

(a) Development of a non-functional scaffold using 1,3-ditopic carboxylate ligand 8 by the structural modification of a discrete [6 + 4] metal-organic supramolecule (3); (b) Functional evolution of 3 into an electrochemically-active structure 11 by using a ferrocenyl 1,3-ditopic carboxylate ligand (10).

Scheme 5

Functional evolution of a discrete [6 + 4] metal-organic supramolecule (3) to modified structure 13 relying on tunable host-guest chemistry towards coronene.