Panchao Yin

Nanoscale Chiral Rod-like Molecular Triads Assembled from Achiral Polyoxometalates

The assembly of two achiral POMs of Lindqvist and Anderson through strong covalent linkages, using bifunctional TRIS with a rotatable C-N single bond, gives two nanoscale rod-like chiral molecular triads with C(2) symmetry, the chirality of which were confirmed by the single crystal X-ray diffraction analyses and solid CD spectroscopy measurements. The enantiopure crystals of these compounds have been obtained by spontaneous resolution upon crystallization in the absence of any chiral source. The present work opens a way to make chiral nanostructures from achiral polyoxoanions, which may have potential applications in asymmetric catalysis, NLO, and ferroelectric materials.

Inorganic–Organic Hybrid Vesicles with Counterion- and pH-Controlled Fluorescent Properties

Two inorganic-organic hybrid clusters with one or two covalently linked pyrene fluorescent probes, [(n-C(4)H(9))(4)N](2)[V(6)O(13){(OCH(2))(3)C(NH(CO)CH(2)CH(2)CH(2)C(16)H(9))}{(OCH(2))(3)C-(NH(2))}] ((TBA(+))(2)1) and [(n-C(4)H(9))(4)N](2)[V(6)O(13){(OCH(2))(3)C(NH(CO)CH(2)CH(2)CH(2)C(16)H(9))}(2)] ((TBA(+))(2)2), respectively, are synthesized from Lindqvist type polyoxometalates (POMs). The incorporation of pyrene into POMs results in amphiphilic hybrid molecules and simultaneously offers a great opportunity to study the interaction between hybrid clusters and their counterions. 2D-NOESY NMR and fluorescence techniques have been used to study the role of counterions such as tetrabutyl ammonium (TBA) in the vesicle formation of the hybrid clusters. The TBA(+) ions not only screen the electrostatic repulsions between the POM head groups but also are involved in the hydrophobic region of the vesicular structure where they interrupt the formation of pyrene excimers that greatly perturbs the luminescence signal from the vesicle solution. By replacing the TBA(+) counterions with protons, the new vesicles demonstrate interesting pH-dependent fluorescence properties.

Polyoxometalatocyclophanes: Controlled Assembly of Polyoxometalate-Based Chiral Metallamacrocycles from Achiral Building Blocks

The first polyoxometalatocyclophanes have been synthesized by the covalent linkage of a hexamolybdate cluster and bisarylimido ligands containing flexible chains. These metallamacrocycles are chiral, and some of them can undergo spontaneous resolution. The work provides a new protocol for preparing chiral polyoxometalates (POMs) and chiral metallamacrocycles from achiral building blocks by fastening both ends of a flexible chain onto an achiral POM to remove the symmetric center and mirror.

Controllable Self-Assembly of Organic-Inorganic Amphiphiles Containing Dawson Polyoxometalate Clusters

An organic-inorganic molecular hybrid containing the Dawson polyoxometalate, ((C(4)H(9))(4)N)(5)H[P(2)V(3)W(15)O(59)(OCH(2))(3)CNHCOC(15)H(31)], was synthesized and its surfactant-like amphiphilic properties, represented by the formation of bilayer vesicles, were studied in polar solvents. The vesicle size decreases with both decreasing hybrid concentration and with increasing polarity of the solvent, independently. The self-assembly behavior of this hybrid can be controlled by introducing different counterions into the acetonitrile solutions. The addition of ZnCl(2) and NaI can cause a gradual decrease and increase of vesicular sizes, respectively. Tetraalkylammonium bromide is found to disassemble the vesicle assemblies. Moreover, the original counterions of the hybrid can be replaced with protons, resulting in pH-dependent formation of vesicles in aqueous solutions. The hybrid surfactant can further form micro-needle structures in aqueous solutions upon addition of Ca(2+) ions.

Bottom-Up Construction of POM-Based Macrostructures: Coordination Assembled Paddle-Wheel Macroclusters and Their Vesicle-like Supramolecular Aggregation in Solution

A bottom-up approach to obtain nanoclusters and large, uniform vesicle-like structures containing organic functionalized hexamolybdates in solution state were developed. Hexamolybdate functionalized carboxylic acid coordinated with two copper ions to form paddle-wheel tetrapolyoxometalate clusters with the features of macro-ions, which can spontaneously assemble into large, stable blackberry-type structures in suitable solvents, completing a hierarchical organization from small POM molecules to nanoscale complexes and then to supramolecular structures.

Single‐Side Organically Functionalized Anderson‐Type Polyoxometalates

Polyoxometalate (POM)-based organic–inorganic hybrid materials have attracted extensive attention in the last ten years due to their potential applications in catalysis, nonlinear optics, photovoltaic, and self-assembly research. Currently, trisalkoxo tripodal ligand (Tris)-functionalized Lindqvist-, Anderson-, and Dawson-type POMs show high stability and varied functionalities. Zubieta et al. used Tris ligands to stabilize macro-POM clusters and to functionalize hexavanadate. The functionalized hexavanadate was further developed by Hill and co-workers for the construction of metal–organic frameworks, which can function as highly efficient heterogeneous catalytic materials. Due to the high reactivity of vanadate, vanadium-containing Dawsontype POMs were observed to be capped by only one Tris ligand. In particular, after Hasenknopf et al. had established the synthesis of Tris derivatives of Anderson-type POMs in 2002, the groups of Cronin and Hasenknopf introduced different kinds of functional groups to the system through further organic reactions. The resulting materials show interesting functions including high biological activity against cells, photocatalytic properties, and interesting selfassembly behavior. Due to their high symmetry (D3d), both sides of Anderson-type POMs are easily functionalized simultaneously by Tris ligands during their synthesis, which seems to be an unquestionable fact (Figure 1), and there has never been any report on a single-sided functionalized Anderson-type POM with Tris. Herein, we report the synthesis and characterization of Anderson-type POMs with only one side functionalized by a Tris ligand, which not only afforded asymmetric POM-based hybrid materials for further research, but also uncovered more structural and reactive properties of Anderson-type POMs, and the reaction mechanism for the functionalization of POMs with Tris. In the previous protocol, to synthesize the double-sided functionalized Anderson-type POMs, octamolybdate, a salt of the central heteroatom, and organic ligands (Tris) were mixed in an organic solvent, such as acetonitrile, and the final products were obtained after heating to reflux for approximately 16 hours, which is a classical one-pot reaction. However, our new protocol to synthesize the single-side organically functionalized Anderson-type POM, [(C4H9)4N]5{H7ACHTUNGTRENNUNG[HOCH2C ACHTUNGTRENNUNG(CH2)3 ACHTUNGTRENNUNG(CrO6)Mo6O18]2} (1), is a two-step aqueous reaction with high yield through the direct functionalization of the parent Anderson-type POM, [CrMo6O18(OH)6] 3 . Compound [CrMo6O18(OH)6] 3 was first synthesized according to Perloff s method reported in 1970. Pentaerythritol was then added to the resulting aqueous solution of [CrMo6O18(OH)6] 3 , and the mixture was refluxed at once for a prolonged time to finish the esterification. Interestingly, the reaction is of high yield and high selectivity for the mono Tris-functionalized product 1, probably due to the hierarchical synthesis protocol and aqueous reaction media (see the Experimental Section). In the preparation reaction, a single-side-functionalized Anderson-type POM is obtained in high yield (based on Mo), even when the ratio of Tris to the parent Anderson-type POM is two or much higher than two. Therefore, the selectivity for producing such single-sided species might be related to the aqueous environment. [a] P. Wu, P. Yin, Dr. J. Zhang, Dr. J. Hao, Dr. Z. Xiao, Prof. Dr. Y. Wei Department of Chemistry, Tsinghua University Beijing, 100084 (P.R. China) Fax: (+86)10-6277-1149 E-mail : yinpanchao@tsinghua.org.cn yonggewei@tsinghua.edu.cn [b] P. Wu Institute of POM-based Materials Key Laboratory of Fermentation Engineering (Ministry of Education) Hubei University of Technology Wuhan, 430068 (P.R. China) [c] Prof. Dr. Y. Wei Key Laboratory of Cluster Science (Beijing Institute of Technology) Ministry of Education of China Beijing, 100081 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101552. Figure 1. Molecular structures of: a) unfunctionalized and b) bifunctionalized Anderson-type POMs. Color code: Mo: large black sphere; Cr: central gray sphere; O: small black sphere; C: large gray sphere; H: small gray sphere; X= functional group: -CH2OH, -NH2, -CH3, or -NO2.

Spontaneous Stepwise Self‐Assembly of a Polyoxometalate–Organic Hybrid into Catalytically Active One‐Dimensional Anisotropic Structures

An inorganic-organic hybrid surfactant with a hexavanadate cluster as the polar head group was designed and observed to assemble into micelle structures, which further spontaneously coagulate into a 1D anisotropic structure in aqueous solutions. Such a hierarchical self-assembly process is driven by the cooperation of varied noncovalent interactions, including hydrophobic, electrostatic, and hydrogen-bonding interactions. The hydrophobic interaction drives the quick formation of the micelle structure; electrostatic interactions involving counterions leads to the further coagulation of the micelles into larger assemblies. This process is similar to the crystallization process, but the specific counterions and the directional hydrogen bonding lead to the 1D growth of the final assemblies. Since most of the hexavanadates are exposed to the surface, the 1D assembly with nanoscale thickness is a highly efficient heterogeneous catalyst for the oxidation of organic sulfides with appreciable recyclability.

DMAP-catalyzed esterification of pentaerythritol-derivatized POMs: a new route for the functionalization of polyoxometalates

We have demonstrated that a pentaerythritol-derivatized hexavanadate can be easily esterified with acid anhydrides using 4-(N,N-dimethylamino)pyridine (DMAP) as a catalyst, which provides a convenient method for the functionalization of polyoxometalates.

Palladium‐Catalyzed Heck Reaction of Polyoxometalate‐Functionalised Aryl Iodides and Bromides with Olefins

Organically derivatised polyoxometalate (POM) clusters containing bromo or iodo groups can undergo ligand-free, Pd-catalysed Heck carbon-carbon coupling reactions with alkenes, with bromomagnesium phenylamide as a base (see scheme). This protocol offers a new route to organic-inorganic hybrid molecular materials in which POM clusters are covalently bonded with organic conjugated segments.

{Mo24Fe12} Macrocycles: Anion Templation with Large Polyoxometalate Guests

POM and circumstance: Nanometer-sized polyoxometalates (POMs) bring a new direction to anion-templated supramolecular chemistry. The Keggin (left) and Dawson-type (right) polyoxoanions direct the assembly of giant metallomacrocycles through an array of weak hydrogen-bonding interactions. The concerted action of multiple hydrogen bonds keeps the templating guests embedded within the hosts, even in the solution state.