The formation of supramolecular host-guest complexes of fullerene (C(60)) and two novel tribenzotriquinacene based hosts (5 a and 5 b) was investigated in solution and in the solid state. Stability constants for 1:1 and 2:1 complexes were obtained from spectroscopic (UV/Vis, (1)H NMR) titration experiments. Association constants of K(1)=(2908+/-360) L mol(-1) and K(2)=(2076+/-300) L mol(-1) for C(60)/5 a, and K(1)=(5608+/-220) L mol(-1) and K(2)=(673+/-160) L mol(-1) for C(60)/5 b were obtained. Single crystal X-ray structural analysis of compound C(60) subset5 b3 toluene revealed that a molecule of C(60) was located at short van der Waals contact distances in the open pre-organised cavity of the rigid host. The supramolecular complex created resembles an engineered nanosized ball joint and represents the first member for a future nanomechanics construction kit.

The synthesis of a structurally optimized tribenzotriquinacene receptor 9 is described, which is extended by centrohexaindane moieties to give rise to a half-round concave ball bearing, with optimum shape complementarity towards C(60) fullerene. Spectroscopic investigations reveal that this novel host forms a 1 : 1 host-guest complex with C(60) with a complex stability constant of K(1) = 14,550 ± 867 M(-1), which is considerably higher than those reported for structurally related tribenzotriquinacene hosts reported previously. Both the suppression for binding of a second receptor (i.e. formation of a 2 : 1 host-guest complex) as well as the increase of complex stability of the 1 : 1 complex can be rationalized in terms of multiple additive van der Waals and π-π interactions between C(60) and the aromatic groups of the receptor, as revealed by DFT + D and force-field calculations. Combining results from spectroscopic and theoretical investigations leads to predictions in light of future receptor designs, which--apart from shape complementarity--will have to consider an optimized electronic match (i.e. partial charge transfer) between the receptor and the fullerene host.

We report the synthesis of a tribenzotriquinacene-based (TBTQ) receptor (3) for C60 fullerene, which is extended by pentiptycene moieties to provide an almost enclosed concave ball bearing. The system serves as a model for a self-assembling molecular rotor with a flexible and adapting stator. Unexpectedly, nuclear magnetic resonance spectroscopic investigations reveal a surprisingly low complex stability constant of K1 =213±37 M(-1) for [C60 ⊂3], seemingly inconsistent with the previously reported TBTQ systems. Molecular dynamics (MD) simulations have been conducted for three different [C60 ⊂TBTQ] complexes to resolve this. Because of the dominating dispersive interactions, the binding energies increase with the contact area between guest and host, however, only for rigid host structures. By means of free-energy calculations with an explicit solvent model it can be shown that the novel flexible TBTQ receptor 3 binds weakly because of hampering entropic contributions.

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Developing a functional Cr(III) electrolyte to replace carcinogenic and toxic Cr(VI) electroplating requires a deeper understanding of the deposition mechanisms. Hence, this study investigates and compares the growth of chromium on inert glassy carbon (GC) electrodes from low-concentration Cr(III) and Cr(VI) electrolytes, using a novel potentiodynamic deposition scheme. This allows the initial stages of deposition to be probed, which are crucial for determining the overall deposition mechanism. Scanning electron microscopy shows that, for both systems, micrometer-sized hexagonal chromium hydride crystals could be deposited on GC, thus serving to be the first reporting of such structures. In addition, by increasing the deposition time, the changes in a particle structure for both systems were tracked; therefore, possible areas of similarity as well as key differences could be identified, which, when addressed may provide a more viable, environmentally friendly trivalent electrolyte for chromium electroplating.