Homohelical Self-Assembly of Trimer of α-Cyclodextrin and Octamolybdate.

The ability to conceptually mimic biomolecules to construct emergency-functional homospiral aggregates remains a long-standing challenge. Herein, we report artificial homohelical assembly by blending inorganic polyoxometalates (POMs) and organic cyclodextrin molecules. The chiral double-helical chains have been achieved by a left-hand arrangement of trimer-trimer. The trimer is formed by three {Mo8}@α-CD inclusive complexes as a Whittaker-style paddle wheel. During the process of assembly, chiral transfer and amplification from molecule to superstructure were observed. The enantioselective adsorption of the homohelical aggregate toward (R/S)-1,1'-binaphthyl-2,2'-diamine was further demonstrated. The interaction of {Mo8} and α-CD in solution was investigated. This work opens a wide scope for the design of a homohelix, enriching POM-based inorganic-organic materials.

Selective Passivation of Surface toward Bright Yellow Defective Emission of CdS Quantum Dots.

CdE (E = S, Se) quantum dots (QDs) with a broad and large Stokes shift PL emission have emerged as potential materials for white-light LEDs. However, this surface-related emission of nanocrystals is currently limited by low quantum efficiency. Herein, a convenient noninjected one-pot method at a relatively low temperature to prepare CdS QDs was readily achieved. The CdS-368 QD displays intense broad yellow emission in both solution and the solid state at room temperature. The coligation of organic and inorganic ligands passivates the electron trap states at the QD surface and suppresses nonradiative recombination, which is responsible for the high stability of colloids in organic solvents and the distinct fluorescence quantum yield.

Doping transition metals to modulate the chirality and photocatalytic activity of rare earth clusters.

In this paper, we report the successful assembly of achiral {Ln6M} ([Ln6M(µ3-OH)8(acac)12(CH3O)x(CH3OH)y], Ln = La, M = Mn, Co, Fe) and chiral {Nd9Fe2} ([Nd9Fe2(µ4-O)(µ3-OH)14(acac)16(NO3)(CH3OH)2(H2O)3]) rare earth clusters using achiral rigid ligands and a transition metal doping strategy. {Ln6M} can be viewed as the fusion of two {Ln3M} tetrahedrons by sharing vertices. {Nd9Fe2} results from the fusion of four {Ln3M} tetrahedrons by vertice and edge sharing. The substitution of Ln with transition metal leads to changes in the coordination pattern around neighboring Ln, which triggers the switch of metal center chirality. This study demonstrates the potentiality of utilizing transition metal doping and rigid ligand to control the chirality of rare earth clusters. In addition, the photocatalytic CO2 activity of these transition metal-doped rare earth clusters has been studied.

The mystery of Ph3PS revealed in magic-size Ag-S cluster nucleation.

The synthesis of atomically precise semiconductors Ag-S clusters is a subject of intense research interest, yet the formation mechanism of such nanoclusters remains obscure due to their uncontrolled fast nucleation process in solution. Herein, we have investigated the reaction mechanism responsible for {Ag32S3} nucleation using UV, ESI-MS, NMR and SCXRD analyses. Triphenylphosphorus sulfide (PPh3S) was surprisingly found to slow down the kinetic process of the cluster nucleation. Furthermore, a key precursor [Ag2(Ph3PS)4]2+ was captured, which was attacked by Agn(CCBut)m and traces of water to generate {Ag32S3}. This mechanism provides valuable new insights into the synthesis of inorganic magic-size clusters.

Supramolecular hybrids of chiral Waugh polyoxometalate with cyclodextrins.

The development of novel systems for chiral polyoxometalates (POMs) is an attractive research field because of their fascinating topological structures and well-defined functions. Herein, we have developed a new reaction route for the synthesis of two unprecedented chiral Waugh POM-based supramolecular architectures. Single-crystal X-ray diffraction reveals that the architectures exhibit a wavy three-dimensional framework and bamboo-rod-connected framework upon regulating the size of the cyclodextrin and the stacking pattern of the D3 symmetric Waugh {MnMo9}. Solution studies using NMR, circular dichroism and isothermal titration calorimetry corroborate nicely the very weak interactions between the components. The intricate chiral microenvironment originating from the hybrid frameworks may be responsible for the selective recognition of the Λ-{MnMo9} enantiomer. This study highlights the importance of the asymmetric configuration of the POM for designing CD/POM assemblies and understanding their chirality.

A chloride-doped silver-sulfide cluster [Ag148S26Cl30(CCBut)60]6+: hierarchical assembly, enhanced luminescence and cytotoxicity to cancer cells.

The formation of high-nuclear silver(I) clusters remains elusive and their potential applications are still underdeveloped. Herein, we report an unprecedented gigantic Ag148 ([Ag148S26Cl30(CCBut)60](SbF6)6) cluster co-templated by Cl- and S2-, which was well-defined by single-crystal X-ray diffraction and high-resolution mass spectrometry. The cluster exhibits a hierarchical structure consisting of fused Ag24X16 kernel, Ag60X20 shell and "cluster of clusters assembling" of four pentagonal concave polyhedral {Ag16X5} units. Furthermore, the silver cluster emits red light at room temperature with a prominent 39.6% QY. The cellular uptake and cytotoxicity indicate that Ag148 induces apoptosis of cancer cells in a dose-dependent manner.

Unusual structural transformation and luminescence response of magic-size silver(I) chalcogenide clusters via ligand-exchange.

Structural transformations of nanoclusters provide a platform to tune their properties and understand the fundamental science due to their intimate structure-property correlation. Here, we present an alkynyl ligand-exchange induced growth of atomically precise silver(I) clusters, which are particularly of interest because of their luminescence response at room temperature. SCXRD and UV-vis map out the growth steps of the cluster from [Ag32S3(CCBut)23]3+ featuring a pseudo-D3h concave Ag32S3 to [Ag45S6(CCPhBr)32]+ with a pseudo-Oh core-shell Ag9S6@Ag24@Ag12, which is driven by a thermodynamic route under the disruption of ligands. To our knowledge, the findings in this work establish the first example of ligand-exchange as a versatile tool for tuning the size and luminescence of semiconductor silver(I) clusters.

Spontaneous and induced chiral symmetry breaking of stereolabile pillar[5]arene derivatives upon crystallisation.

Stereolabile pillar[5]arene (P[5]) derivatives, which are dynamic racemic mixtures in solution on account of their low inversion barriers, were employed as platforms to study chiral symmetry breaking during crystallisation. In the solid state, we showed that crystal enantiomeric excess of a conglomerate-forming P[5] derivative can be obtained by handpicking and Viedma ripening without the intervention of external chiral entities. On the other hand, in the presence of ethyl d/l-lactate as both optically-active solvents and chiral guests, the handedness of P[5] derivative crystals, either forming racemic compounds or conglomerates upon condensation, can be directed and subsequently inverted in a highly controllable manner.

Solvent-driven crystal-crystal transformation and morphology change in a 2D layered inorganic POM-based framework.

In this paper, a pure 2D inorganic POM-based framework underwent a single crystal to single crystal conversion when soaked in organic solvents that are miscible with water, forming a more densely packed identical framework accompanying the formation of nanowires. The change in morphology is closely related to the surface tension of water, and the lower surface tension achieved by dehydration promotes the formation of nanowires, which is revealed by SXRD, PXRD, SEM, TGA and electrochemical impedance spectroscopy (EIS).

A nonconventional host-guest cubic assembly based on γ-cyclodextrin and a Keggin-type polyoxometalate.

Supramolecular self-assembly allows components to organize themselves into regular patterns by using non-covalent interactions to find the lowest-energy configuration. However, self-assembling organic and inorganic building blocks together into an ordered framework remains a challenge due to the difficulties in rationally interfacing two dissimilar materials. Herein, we report on the host-guest ensemble of polyoxometalates (POMs) using cyclodextrins (CDs) as the trapping agent to form POM@γ-CD entities. Two unprecedented super cubic isostructures, Co/Cu-PW12O40-γ-CD, were obtained. The self-assembly has been observed both in solution (MS, 1D NMR and 2D DOSY) and in the solid state. Single-crystal X-ray diffraction reveals that in a unit cell, the inner (POM@γ-CD)12 cube is encapsulated by the outer (POM@γ-CD)24 cube. Besides, due to the rather large spherical voids, two (POM@γ-CD)24 cubes are interspersed together. Preliminary investigations of the redox properties of the [PW12O40]3- encapsulated in the γ-cyclodextrins indicate that the redox properties of the trianion are largely retained, yet an additional electrochemical stabilization is observed. The adduct reported here opens the door to a new generation of hybrid materials with tuned structures and customized functionalities.

Controlling the Reactivity of the [P8 W48 O184 ]40- Inorganic Ring and Its Assembly into POMZite Inorganic Frameworks with Silver Ions.

The construction of pure-inorganic framework materials with well-defined design rules and building blocks is challenging. In this work, we show how a polyoxometalate cluster with an integrated pore, based on [P8 W48 O184 ]40- (abbreviated as {P8 W48 }), can be self-assembled into inorganic frameworks using silver ions, which both enable reactions on the cluster as well as link them together. The {P8 W48 } was found to be highly reactive with silver ions resulting in the in situ generation of fragments, forming {P9 W63 O235 } and {P10 W66 O251 } in compound (1) where these two clusters co-crystallize and are connected into a POMZite framework with 11 Ag+ ions as linkers located inside clusters and 10 Ag+ linking ions situated between clusters. Decreasing both the concentration of Ag+ ions, and the reaction temperature compared to the synthesis of compound (1), leads to {P8 W51 O196 } in compound 2 where the {P8 W48 } clusters are linked to form a new POMZite framework with 9 Ag+ ions per formula unit. Further tuning of the reaction conditions yields a cubic porous network compound (3) where {P8 W48 } clusters as cubic sides are joined by 4 Ag+ ions to give a cubic array and no Ag+ ions were found inside the clusters.

Assembly of Tungsten-Oxide-Based Pentagonal Motifs in Solution Leads to Nanoscale {W48}, {W56}, and {W92} Polyoxometalate Clusters.

We report an approach to synthesize molecular tungsten-oxide-based pentagonal building blocks, in a new {W21 O72} unit, and show how this leads to a family of gigantic molecular architectures including [H12W48O164](28-) {W48}, [H20W56O190](24-) {W56}, and [H12W92O311](58-) {W92}. The {W48} and {W56} clusters are both dimeric species incorporating two {W21} units and the {W56} species is the first example of a molecular metal oxide cluster containing a chiral "double-stranded" motif which is stable in solution as confirmed by mass spectrometry. The {W92} anion having four {W21} units is one of the largest transition metal substituted isopolyoxotungstates known.

Lanthanide-thiophene-2,5-dicarboxylate frameworks: ionothermal synthesis, helical structures, photoluminescent properties, and single-crystal-to-single-crystal guest exchange.

Eight three-dimensional lanthanide-thiophene-2,5-dicarboxylate frameworks, [Ln(TDC)(2)]·(choline) (1-6; Ln = Gd, Nd, Eu, Er, Tb, Dy; TDC = thiophene-2,5-dicarboxylate), [Yb(TDC)(2)(e-urea)]·(choline)·H(2)O (7; e-urea = ethyleneurea), [Nd(2)(TDC)(3)(e-urea)(4)]·3(e-urea) (8) have been successfully prepared in deep eutectic solvents (choline chloride/e-urea), respectively. Compounds 1-7 are anionic frameworks with 8-connected bcu topology, while compound 8 features a neutral 6-connected rob-type framework with guest e-urea molecules. In these structures, lanthanide ions show dicapped trigonal prism, pentagonal bipyramid, and tricapped trigonal prism coordination configurations, respectively, and the TDC ligands exhibit different coordination modes. Versatile helical substructures are presented in these compounds. The photoluminescent properties of compounds 3 (Eu) and 8 (Nd) were studied. Moreover, compound 8 can perform single-crystal-to-single-crystal guest exchange. The ethanol-exchange mechanism of 8 can be ascribed to the kinetically controlled flexibility (KCF).

2-[(2-Carboxy-phen-yl)sulfan-yl]acetic acid.

The title compound, C(9)H(8)O(4)S, affords a zigzig chain in the crystal structure by inter-molecular O-H⋯O hydrogen bonds. The molecular geometry suggests that extensive but not uniform π-electron delocalization is present in the benzene ring and extends over the exocyclic C-S and C-C bonds.

[1-(4-Hydroxy-phen-yl)-1H-tetra-zol-5-ylsulfan-yl]acetic acid.

The title compound, C(9)H(8)N(4)O(3)S, shows a layer structure constructed from inter-molecular O-H⋯O and O-H⋯N hydrogen bonds. Inter-atomic distances suggest that extensive, but not uniform, π-electron delocalization is present in the tetra-zole rings and extends over the exocyclic C-S bond.