The ability to manipulate self-assembly of molecular building blocks is the key to achieving precise "bottom-up" fabrications of desired nanostructures. Herein, we report a rational design, facile synthesis, and self-assembly of a series of molecular Janus particles (MJPs) constructed by chemically linking α-Keggin-type polyoxometalate (POM) nanoclusters with functionalized polyhedral oligomeric silsesquioxane (POSS) cages. Diverse nanostructures were obtained by tuning secondary interactions among the building blocks and solvents via three factors: solvent polarity, surface functionality of POSS derivatives, and molecular topology. Self-assembled morphologies of KPOM-BPOSS (B denotes isobutyl groups) were found dependent on solvent polarity. In acetonitrile/water mixtures with a high dielectric constant, colloidal nanoparticles with nanophase-separated internal lamellar structures quickly formed, which gradually turned into one-dimensional nanobelt crystals upon aging, while stacked crystalline lamellae were dominantly observed in less polar methanol/chloroform solutions. When the crystallizable BPOSS was replaced with noncrystallizable cyclohexyl-functionalized CPOSS, the resulting KPOM-CPOSS also formed colloidal spheres; however, it failed to further evolve into crystalline nanobelt structures. In less polar solvents, KPOM-CPOSS crystallized into isolated two-dimensional nanosheets, which were composed of two inner crystalline layers of Keggin POM covered by two monolayers of amorphous CPOSS. In contrast, self-assembly of KPOM-2BPOSS was dominated by crystallization of the BPOSS cages, which was hardly sensitive to solvent polarity. The BPOSS cages formed the crystalline inner bilayer, sandwiched by two outer layers of Keggin POM clusters. These results illustrate a rational strategy to purposely fabricate self-assembled nanostructures with diverse dimensionality from MJPs with controlled molecular composition and topology.

Polyoxometalate molybdenum blue (MB) complexes typically exist as discrete multianionic clusters and are composed of repeating Mo building units. MB wheels such as {Mo 176 } and {Mo 154 } are made from pentagon-centered {Mo 8 } building blocks joined by equal number of {Mo 1 } units as loin, and {Mo 2 } dimer units as skirt along the ring edge, with the ring sizes of the MB wheels modulated by the {Mo 2 } units. Herein we report a new class of contracted lanthanide-doped MB structures that have replaced all the {Mo 2 } units with lanthanide ions on the inner rim, giving the general formula {Mo 90 Ln 10 }. We show three examples of this new decameric {Mo 90 Ln 10 } (Ln = La, Ce, and Pr) framework synthesized by high temperature reduction and demonstrate that later Ln ions result in {Mo 92 Ln 9 } (Ln = Nd, Sm), conserving one {Mo 2 } linker unit in its structure, as a consequence of the lanthanide contraction. Remarkably the {Mo 90 Ln 10 } compounds are the first examples of chargeneutral molybdate wheels as confirmed by BVS, solubility experiments, and redox titrations. We detail our full synthetic optimization for the isolation of these clusters and complete characterization by X-ray, TGA, UV-vis, and ICP studies. Finally, we show that this fine-tuned self-assembly process can be utilized to selectively enrich Ln-MB wheels for effective separation of lanthanides.

A series of rod-shaped polyoxometalates (POMs) [Bu N] [Mo O NC(CH O) MnMo O (OCH ) CNMo O ] and [Bu N] [ArNMo O NC(CH O) MnMo O (OCH ) CNMo O NAr] (Ar=2,6-dimethylphenyl, naphthyl and 1-methylnaphthyl) were chosen to study the effects of cation-π interaction on macroionic self-assembly. Diffusion ordered spectroscopy (DOSY) and isothermal titration calorimetry (ITC) techniques show that the binding affinity between the POMs and Zn ions is enhanced significantly after grafting aromatic groups onto the clusters, leading to the effective replacement of tetrabutylammonium counterions (TBAs) upon the addition of ZnCl . The incorporation of aromatic groups results in the significant contribution of cation-π interaction to the self-assembly, as confirmed by the opposite trend of assembly size vs. ionic strength when compared with those without aromatic groups. The small difference between two aromatic groups toward the Zn ions is amplified after combining with the clusters, which consequently triggers the self-recognition behavior between two highly similar macroanions.

Abstract:Incorporating the building blocks of nature (e.g., peptides and DNA) into inorganic polyoxometalate (POM) clusters is a promising approach to improve the compatibilities of POMs in biological fields. To extend their biological applications, it is necessary to understand the importance of different non-covalent interactions during self-organization. A series of Anderson POM-peptide hybrids have been used as a simple model to demonstrate the role of different interactions in POM-peptide (biomolecules) systems. Regardless of peptide chain length, these hybrids follow similar solution behaviors,

The predesigned metal-organic macrocycle ZnQDB(NO) (Zn-QDB) was observed to self-assemble into a hollow, spherical, single-layered "blackberry"-type structure. The self-assembly behaviors of the Zn-QDB are significantly influenced by additional small ions. Specifically, the cations exhibit strong co-ion effects on the interaction between cationic macrocycles which are different from the previously reported co-ion effects of simple anions on anionic polyoxometalates. This unusual phenomenon is due to the unique cation-π interaction between small cations and electron-rich cavity of Zn-QDB, as confirmed by UV-vis, H NMR, and fluorescence spectra. The variation of hydrodynamic radius (R) of assemblies with the changes of solution ionic strength and the type of cations reveals the competition between counterion-mediated attraction and cation-π interaction during the self-assembly process. Furthermore, the cooperativity of cation-π interaction and π-π stacking play a vital role in enhancing the stability of the supramolecular structure.

The dilute solutions behaviors of Pd L metal-organic nanocage and its two PEGylated derivatives are explored. The basic nanocages can self-assemble into vesicle-like blackberry structures in polar solvents via counterion-mediated attraction, whereas the PEGylated nanocages always stay as discrete ions under the same conditions, demonstrating that the PEGylation can improve the stability of the single nanocages. In addition, larger nanocages are found to self-assemble in less polar solvents.

Two sequence isomeric giant surfactants exhibit distinguished self-assembly behaviors, which is caused by the different molecular packing conformations induced by their distinct molecular sequences.

We observe the formation of highly controllable and responsive onion-like vesicles by using rigid sphere−rod amphiphilic hybrid macromolecules, composed of charged, hydrophilic Keggintype clusters (spheres) and hydrophobic rod-like oligofluorenes (OFs). Unlike the commonly used approach, which mainly relies on chain bending of flexible molecules to satisfy different curvatures in onion-like vesicles, the rigid hybrids form flexible interdigitations by tuning the angles between OFs, leading to the formation of bilayers with different sizes. The self-assembled vesicles possess complete onion-like structures from most inner to outer layers, and their size (layer number) can be accurately manipulated by different solution conditions including solvent polarity, ionic strength, temperature, and hybrid concentration, with fixed interbilayer distance under all conditions. Moreover, the vesicle size (layer number) shows excellent reversibility to the change of temperature. The charged feature of spheres, rod length, and overall hybrid architecture shows significant effects on the formation of such onion-like vesicles.