Kong-qiu Hu

Solvent‐Dependent Synthesis of Porous Anionic Uranyl–Organic Frameworks Featuring a Highly Symmetrical (3,4)‐Connected ctn or bor Topology for Selective Dye Adsorption

Two highly symmetrical (3,4)-connected uranyl-organic frameworks (UOFs) were synthesized by a judicious combination of D3h -symmetrical triangular [UO2 (COO)3 ]- and Td symmetrical tetrahedral tetrakis(4-carboxyphenyl)methane (H4 MTB). These two as-synthesized UOFs possess similar structural units and coordination modes but totally different topological structures, namely ctn net and bor net. Solvent-induced interpenetration and a morphology change are observed. The two compounds exhibit crystal transformation via a dissolution-crystallization process. Adsorption experiments in CH3 OH solution indicate that both of them can selectively remove positively charged dyes over negatively charged and neutral dyes. Moreover, the electronic structural and bonding properties of the two compounds were systematically explored by density functional theory (DFT) calculations.

An Unprecedented Two‐Fold Nested Super‐Polyrotaxane: Sulfate‐Directed Hierarchical Polythreading Assembly of Uranyl Polyrotaxane Moieties

The hierarchical assembly of well-organized submoieties could lead to more complicated superstructures with intriguing properties. We describe herein an unprecedented polyrotaxane polythreading framework containing a two-fold nested super-polyrotaxane substructure, which was synthesized through a uranyl-directed hierarchical polythreading assembly of one-dimensional polyrotaxane chains and two-dimensional polyrotaxane networks. This special assembly mode actually affords a new way of supramolecular chemistry instead of covalently linked bulky stoppers to construct stable interlocked rotaxane moieties. An investigation of the synthesis condition shows that sulfate can assume a vital role in mediating the formation of different uranyl species, especially the unique trinuclear uranyl moiety [(UO2 )3 O(OH)2 ](2+) , involving a notable bent [O=U=O] bond with a bond angle of 172.0(9)°. Detailed analysis of the coordination features, the thermal stability as well as a fluorescence, and electrochemical characterization demonstrate that the uniqueness of this super-polyrotaxane structure is mainly closely related to the trinuclear uranyl moiety, which is confirmed by quantum chemical calculations.

Supramolecular Isomers of Coordination-Directed Side-Chain Polypseudorotaxanes Based on Trimeric Uranyl Oxalate Nodes.

Although the prosperity of rotaxane coordination polymers with rotaxane molecules serving as main-chain linkers is known, side-chain metal-organic polypseudorotaxanes incorporating macrocyclic host molecules have not been reported to date. Herein a new type of coordination-driven cucurbit[6]uril-bearing side-chain polypseudorotaxane, with two-dimensional trimeric uranyl-oxalate as main chains, has been synthesized. This was carried out through hydrothermal reactions of uranyl components with an in situ-formed carboxylated pseudorotaxane ligand in the presence of oxalate co-ligands. Varying the substitution site of coordination groups led to two different supramolecular isomers. Further mechanistic analysis indicated that condition-dependent hydrolysis of the cyano groups of the pseudorotaxane ligand, as well as the participation of oxalate groups into the coordination sphere of uranyl moieties, contributes to the formation of this new type of side-chain polypseudorotaxane.

Stepwise ortho Chlorination of Carboxyl Groups for Promoting Structure Variance of Heterometallic Uranyl–Silver Coordination Polymers of Isonicotinate

We report the syntheses and characterization of four new heterometallic uranyl-silver compounds from isonicotinic acid derivatives with a stepwise ortho chlorination of carboxyl group, that is, isonicotinic acid (H-PCA), 3-chloroisonicotinic acid (H-3-MCPCA), and 3,5-dichloroisonicotinic acid (H-3,5-DCPCA). Compound 1, (UO2)Ag4(3,5-DCPCA)6(3,5-DCPy)2, from H-3,5-DCPCA displays a heterometallic three-dimensional (3D) framework through the connection of 3,5-DCPCA and in situ-formed 3,5-dichloropyridine (3,5-DCPy) with the aid of multiple argentophilic interactions. Compounds 2 ((UO2)Ag(3-MCPCA)3) and 3 ((UO2)Ag2(3-MCPCA)4), which differ from each other in coordination modes of uranyl center, are both heterometallic 3D reticular frameworks from 3-MCPCA based on highly coordinated silver nodes. All these heterometallic uranyl-silver compounds are different from the hydrothermal products from chlorine-free H-PCA ligand in the presence of uranyl and silver ions, U-Ag-PCA ((UO2Ag(OH)(PCA)2)) and 4 ((UO2)Ag2(OH)(H2O)2(PCA)4) due to highly coordinated silver ions found in 1-3, among which carboxyl groups of isonicotinate expected to coordinate with uranyl are the biggest contributors. Detailed structural analysis reveals that the inclination of the carboxyl group of isonicotinate driven by large steric hindrance from bulky ortho chlorine atoms at its ortho positions enables it to participate in the coordination sphere of silver ion and promote the formation and structure variance of 3D heterometallic uranyl-silver frameworks.

Uranyl-containing heterometallic coordination polymers based on 4-(4’-carboxyphenyl)-1,2,4-triazole ligand: Structure regulation through subtle changes of the secondary metal centers

Abstract Three uranyl-containing coordination polymers, Cd(UO2)2(cpt)4(bdc)(H2O)2 (1), Zn(UO2)2(cpt)4(bdc)(H2O)2 (2) and UO2(OH)(cpt) (3) (Hcpt =4-(4’-carboxyphenyl)-1,2,4triazole, H2bdc =1,4-benzenedicarboxylic acid), have been synthesized under hydrothermal conditions by employing a bifunctional ligand (Hcpt) with both O-donors and N-donors. Compound 1 represents a 3-D framework with the point symbol of (62·84)(62·8)2 by the intersection of two sets of 1-D [Cd2(UO2)2(cpt)4(bdc)]n loop chains extended along different directions. Compound 2 exhibits a 2-nodal (3,4)-connected 2-D network with the point symbol (4·62)2(42·62·82). Compound 3 shows a 2-D network by the assembly of uranyl dimers and the cpt- anions. Although 1 and 2 have similar chemical formulas and the same coordination modes of ligands and metal centers, they possess totally different molecular frameworks, derived from the different radii of the secondary metal centers, Cd(II) and Zn(II). In addition, the optimal synthesis condition, thermal stability, luminescent properties, and IR spectra of 1 and 2 were also investigated. Graphical Abstract

Actinide-Based Porphyrinic MOF as a Dehydrogenation Catalyst

Uranyl-organic frameworks (UOFs) have recently been the object of many research endeavors due to the unique coordination mode of uranyl ions and their attractive physicochemical properties. Here, a new (3,4)-connected UOF (U-IHEP-4) assembled from uranyl and porphyrin ligand tetrakis(4-carboxyphenyl)porphyrin (H4TCPP) is reported, which represents the first case of actinide porphyrinic MOFs. Adsorption experiments in DMF solution demonstrated that U-IHEP-4 selectively adsorbs positively charged dyes, which is in line with its negatively charged framework and large pore volume ratio (90 %). Remarkably, U-IHEP-4 exhibited high catalytic activity for the dehydrogenation of N-heterocycles to synthesize the corresponding aromatic heterocycles and it can be used as an efficient heterogeneous catalyst.