Xin-Xiong Li

Cubic Polyoxometalate−Organic Molecular Cage

Tris(hydroxymethyl)aminomethane (Tris) was successfully grafted onto the surface of a Ni(6)-substituted polyoxotungstate formed in situ to further generate a three-connected polyoxometalate building block. The cooperative assembly of Tris functionalized three-connected building blocks and rigid 1,3,5-benzenetricarboxylate gave rise to an unprecedented cubic polyoxometalate-organic molecular cage with high thermal and hydrothermal stability.

Designed Assembly of Heterometallic Cluster Organic Frameworks Based on Anderson-Type Polyoxometalate Clusters.

A new approach to prepare heterometallic cluster organic frameworks has been developed. The method was employed to link Anderson-type polyoxometalate (POM) clusters and transition-metal clusters by using a designed rigid tris(alkoxo) ligand containing a pyridyl group to form a three-fold interpenetrated anionic diamondoid structure and a 2D anionic layer, respectively. This technique facilitates the integration of the unique inherent properties of Anderson-type POM clusters and cuprous iodide clusters into one cluster organic framework.

Imidazolium-Based Porous Organic Polymers: Anion Exchange-Driven Capture and Luminescent Probe of Cr2O72–

A series of imidazolium-based porous organic polymers (POP-Ims) was synthesized through Yamamoto reaction of 1,3-bis(4-bromophenyl)imidazolium bromide and tetrakis(4-bromophenyl)ethylene. Porosities and hydrophilicity of such polymers may be well tuned by varying the ratios of two monomers. POP-Im with the highest density of imidazolium moiety (POP-Im1) exhibits the best dispersity in water and the highest efficiency in removing Cr2O7(2-). The capture capacity of 171.99 mg g(-1) and the removal efficiency of 87.9% were achieved using an equivalent amount of POP-Im1 within 5 min. However, no Cr2O7(2-) capture was observed using nonionic analogue despite its large surface area and abundant pores, suggesting that anion exchange is the driving force for the removal of Cr2O7(2-). POP-Im1 also displays excellent enrichment ability and remarkable selectivity in capturing Cr2O7(2-). Cr(VI) in acid electroplating wastewater can be removed completely using excess POP-Im1. In addition, POP-Im1 can serve as a luminescent probe for Cr2O7(2-) due to the incorporation of luminescent tetraphenylethene moiety.

Four‐Shell Polyoxometalates Featuring High‐Nuclearity Ln26 Clusters: Structural Transformations of Nanoclusters into Frameworks Triggered by Transition‐Metal Ions

A series of polyoxometalates (POMs) that incorporate the highest-nuclearity Ln clusters that have been observed in such structures to date (Ln26  , Ln=La and Ce) are described, which exhibit giant multishell configurations (Ln⊂W6 ⊂Ln26 ⊂W100 ). Their structures are remarkably different from known giant POMs that feature multiple Ln ions. In particular, the incorporated Ln-O clusters with a nuclearity of 26 are significantly larger than known high-nuclearity (≤10) Ln-O clusters in POM chemistry. Furthermore, they also contain the largest number of La and Ce centers for any POM reported to date and represent a new kind of rare giant POMs with more than 100 W atoms. Interestingly, the La26 -containing POM can undergo a single-crystal to single-crystal structural transformation in the presence of various transition-metal ions, such as Cu2+ , Co2+ , and Ni2+ , from an inorganic molecular nanocluster into an inorganic-organic hybrid extended framework that is built from POM building blocks with even higher-nuclearity La28 clusters bridged by transition-metal complexes.

Giant Hollow Heterometallic Polyoxoniobates with Sodalite-Type Lanthanide–Tungsten–Oxide Cages: Discrete Nanoclusters and Extended Frameworks

The first series of niobium-tungsten-lanthanide (Nb-W-Ln) heterometallic polyoxometalates {Ln12 W12 O36 (H2 O)24 (Nb6 O19 )12 } (Ln=Y, La, Sm, Eu, Yb) have been obtained, which are comprised of giant cluster-in-cluster-like ({Ln12 W12 }-in-{Nb72 }) structures built from 12 hexaniobate {Nb6 O19 } clusters gathered together by a rare 24-nuclearity sodalite-type heterometal-oxide cage {Ln12 W12 O36 (H2 O)24 }. The Nb-W-Ln clusters present the largest multi-metal polyoxoniobates and a series of rare high-nuclearity 4d-5d-4f multicomponent clusters. Furthermore, the giant Nb-W-Ln clusters may be isolated as discrete inorganic alkali salts and can be used as building blocks to form high-dimensional inorganic-organic hybrid frameworks.

Composite Hybrid Cluster Built from the Integration of Polyoxometalate and a Metal Halide Cluster: Synthetic Strategy, Structure, and Properties

A step-by-step synthetic strategy, setting up a bridge between the polyoxometalate (POM) and metal halide cluster (MHC) systems, is demonstrated to construct an unprecedented composite hybrid cluster built up from one high-nuclearity cationic MHC [Cu8I6](2+) and eight Anderson-type anionic POMs [HCrMo6O18(OH)6](2-) cross-linked by a tripodal alcohol derivative.

Hydrothermal Combination of Trilacunary Dawson Phosphotungstates and Hexanickel Clusters: From an Isolated Cluster to a 3D Framework

Three novel hexa-Ni-substituted Dawson phosphortungstates [Ni6 (en)3 (H2O)6 (μ3-OH)3 (H3 P2 W15 O56 )]⋅14 H2O (1), [Ni(enMe)2 (H2O)][Ni6 (enMe)3 (μ3-OH)3 (H2O)6 (HP2 W15 O56)]⋅ 10 H2O (2), and [Ni(enMe)2 ]3 [Ni(enMe)2 (H2O)][Ni(enMe)(H2O)2][Ni6 (enMe)3 (μ3-OH)3 (Ac)2 (H2O)(P2 W15 O56)]2 ⋅6 H2O (3) (en=ethylenediamine, enMe=1, 2-diaminopropane, Ac=CH3 COO(-)) have been made under hydrothermal conditions and were characterized by IR spectroscopy, elemental analysis, diffuse reflectance spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. The common structural features of compounds 1-3 contain the similar hexa-Ni-substituted Dawson polyoxometalate (POM) units that can be viewed as a [Ni6 (μ3-OH)3](9+) cluster capping on a [P2 W15 O56](12-) fragment. Compounds 1 and 2 are two isolated clusters, whereas compound 3 is the first 3D POM framework constructed from hexa-Ni-substituted Dawson POM units and Ni(enMe) complex bridges. The preparations of compounds 1-3 not only indicate that triangle coplanar Ni6 clusters are very stable fragments in both trivacant Keggin and trivacant Dawson POM systems, but also offer that the hydrothermal technique can act as an effective strategy for making novel Dawson-type high-nuclear transition-metal cluster substituted POMs by combination of lacunary Dawson precusors with transition-metal cations in the tunable role of organic ligands. In addition, magnetic measurements illustrate that there exist overall ferromagnetic interactions in compound 3.

A durable luminescent ionic polymer for rapid detection and efficient removal of toxic Cr2O72

A durable luminescent imidazolium-based main-chain ionic polymer (IMIP-Br) was prepared by a facile quaternization reaction of tri(4-imidazolylphenyl)amine and 1,2,4,5-tetrakis(bromomethyl)benzene. IMIP-Br can not only detect Cr2O72− rapidly and estimate its concentration in water, but also capture Cr2O72− quickly via anion exchange. The tremendous exchange capacity of 318 mg g−1 and remarkable efficiency of 92.6% are achieved using an equivalent amount of IMIP-Br. The separation and recycling procedures are simplified by the integration of Fe3O4 particles and IMIP-Br. The resultant IMIP-Fe shows outstanding enrichment ability, good regenerative ability and superior recyclability for removal of Cr2O72−. The combination of promising removal performances and simple magnetic separation endows IMIP-Fe with great promises for capture and separation of Cr2O72− from contaminated water systems.

Solvent-mediated crystal-to-crystal transformations from a cationic homometallic metal–organic framework to heterometallic frameworks

Two unprecedented heterometallic metal–organic frameworks (MOFs), Ag2(btr)2Cr2O7·0.5H2O (1) and Ag9(btr)6(Cr2O7)4·PF6·6H2O (2) [btr = 4,4′-bis(1,2,4-triazole)], were synthesized through crystal-to-crystal transformation when the monometallic MOF Ag2(btr)2·2ClO4·3H2O was immersed in the aqueous solutions of KPF6–K2Cr2O7 and NaBF4–K2Cr2O7, respectively. The transformation follows a solvent-mediated anion-induced mechanism through the dissolution–reaction–crystallization process. Single-crystal X-ray diffraction analyses reveal that both 1 and 2 are three-dimensional structures based on Ag+, Cr2O72− and btr. In 1, Cr2O72− adopts a bidentate bridging mode, and Ag+ ions are linked by Cr2O72− and btr into a neutral framework. However, Cr2O72− in 2 exhibits two types of unprecedented bridging modes through bridging four and five Ag+ ions. Ag+ ions in 2 are bridged by Cr2O72− and btr to form a cationic framework. The non-coordinated BF4−/PF6− anions show a structure-directing effect during the crystal-to-crystal transformations and can be considered as structure-directing agents. The second-harmonic-generation (SHG) measurement shows that 1 is a non-linear optical complex.

The First 3‐Connected SrSi2‐Type 3D Chiral Framework Constructed from {Ni6PW9} Building Units

A novel 3-connected SrSi2 -type 3D chiral framework constructed from hexa-Ni(II) -cluster-substituted polyoxometalate (POM) units [Ni(enMe)2 ]3 [WO4 ]3 [Ni6 (enMe)3 (OH)3 PW9 O34 ]2 ⋅9H2 O (1) (enMe=1,2-diaminopropane) has been made from a hydrothermal synthetic method. This POM represents the first 3D framework based on {Ni6 PW9 } units and {WO4 } connectors.