Control over the Self-Assembly and Dynamics of Metallacarborane Nanorotors by the Nature of the Polymer Matrix: A Solid-State NMR Study

Solids that combine long-range order with rapid molecular reorientation offer a promising approach for the development of a novel class of functional materials with potential applications in materials science and nanotechnology. In this contribution, the capability of dicarbollide ions to undergo self-assembly processes with suitable macromolecules is demonstrated, and a strategy leading to the formation of structurally and dynamically well-defined amphidynamic polymeric composites is introduced. For this purpose, three amphidynamic nanocomposites were synthesized via the self-assembly of cobalt bis­(dicarbollide) anions (CoD–), with neutral poly­(ethylene oxide) (PEO), and two isomers of poly­(vinylpyridine), P2VP and P4VP, in protonated form. All of the systems were characterized by a combined study employing WAXS, advanced solid-state NMR, and quantum chemical calculations. It was found out that the interaction of neutral PEO with CoD– ions driven by weak dihydrogen bonding resulted in the formation of a uniquely organized periodic structure. In contrast, the self-assembly of the systems based on the electrostatic interactions (charge-transfer-assisted hydrogen bonding) of P2(4)­VP was controlled by the position of the positive charge in pyridine ring and resulted in unique well-defined orientations of the CoD– ions (parallel and perpendicular) with respect to the polymer chains. In addition, the CoD– ions exhibited uniaxial relatively large-amplitude rotational motions in all of the nanocomposites over the broad range of Tg. The motional amplitudes executed by the CoD– ions are significantly more extensive than those of the polymer segments in all of the systems. Macromolecules thus represent a rigid support (stator) for the more mobile CoD– ions (rotators). The obtained findings revealed that a relatively simple self-assembly procedure could be used for the preparation of well-defined amphidynamic nanocomposites, thereby opening a route to construct sophisticated supramolecular systems.