Xinfang Liu

A Foldamer-Based Chiroptical Molecular Switch That Displays Complete Inversion of the Helical Sense upon Anion Binding

Chiral indolocarbazole dimers fold into a helical conformation by virtue of intramolecular hydrogen bonds, as demonstrated by (1)H NMR and CD spectra and optical rotations. In particular, the optical properties of the dimers were found to be extremely sensitive to the nature of the solvent, depending on whether they are folded or not. The helical sense of the dimers can be reversibly switched by binding sulfate ion, which gives rise to complete inversion of the CD spectra. The binding mode and absolute stereochemistry of the sulfate complexes was unequivocally determined by single-crystal X-ray structures, which are all consistent with the CD and (1)H NMR spectra in solution.

Hydrothermal syntheses, structures and luminescent properties of d10 metal–organic frameworks based on rigid 3,3′,5,5′-azobenzenetetracarboxylic acid

Four novel d10 metal–organic frameworks based on rigid 3,3′,5,5′- azobenzenetetracarboxylic acid (H4abtc) in the presence of auxiliary 2,2′-biimidazole (biim), 1,10-phenanthroline (phen) and pyridine (py) have been synthesized under hydrothermal conditions and structurally characterized. Their formulae are [Cd2(abtc)(biim)2]n (1), {[Cd(abtc)0.5(phen)]4·4H2O}n (2), {[Zn(abtc)0.5(phen)]4·2H2O}n (3) and [Zn3(abtc)(py)4(OH)2]n (4). Complex 1 possesses a one-dimensional (1D) infinite tubular structure by using biim as auxiliary ligand. The structures of complexes 2 and 3 exhibit three-dimensional (3D) (4,4)-connected frameworks with (4284) topologys by employing phen as auxiliary ligands. By utilizing py as auxiliary ligand, complex 4 is a (2,3,4)-connected framework with a (10)(83)2(8,105) topology in which there exists -{Zn-O-Zn}- zigzag chains and 46-member macrocycles which are linked by multicarboxylate ligands to form a 3D supramolecular structure. The structural differences among 1–4 indicate the importance of the auxiliary ligands for the framework formation of the coordination polymers. In addition, the thermal stabilities and photoluminescence properties of 1–4 are also investigated.

A Twofold Interpenetrating Porous Metal−Organic Framework with High Hydrothermal Stability: Structure and Gas Sorption Behavior

A twofold interpenetrating polyhedron-based metal-organic framework with high hydrothermal stability was prepared using a rigid and bent C(2)-symmetric ligand containing two 3,5-benzenedicarboxylate units, which have large surface area and high uptake capacities for various gas molecules.

Novel 48-membered hexadecanuclear and 60-membered icosanuclear manganese metallamacrocycles.

Either an S 8 symmetrical 48-membered hexadecanuclear or an S 10 symmetrical 60-membered icosanuclear manganese metallamacrocycle was self-assembled using a manganese ion and a ditopic pentadentate ligand. This was either N-4-phenylbenzoylsalicylhydrazide (H 3pbshz) containing a rigid rod-shaped, bulky biphenyl residue as a terminal N-acyl group or N-3,3-diphenylpropionylsalicylhydrazide (H 3dppshz) containing a flexible beta-branched N-acyl group, but with two sterically bulky phenyl residues at the Cbeta position. The backbone of these metal-organic assemblies is a repeating unit consisting of a -[Mn-N-N-] link that extends to complete either the 48-membered cyclic structure involving 16 manganese(III) centers and 16 ditopic linker ligands or the 60-membered cyclic structure involving 20 manganese(III) centers and 20 ditopic linker ligands (depending on the ligand used). Even though the nuclearity of the metallamacrocycles was different, the successive manganese centers were in the same chiral sequence, ...(LambdaLambdaDeltaDelta)(LambdaLambdaDeltaDelta)....

A two-fold interpenetrated (3,6)-connected metal–organic framework with rutile topology showing a large solvent cavity

A two-fold interpenetrated metal–organic framework (MOF), [(Zn4O)2L4(DMF)2(H2O)3], was prepared using the tritopic ligand 4,4′,4′′-[1,3,5-benzenetriyltris(carbonylimino)]trisbenzoic acid (H3L) and zinc nitrate. The MOF, based on the hexatopic tetranuclear Zn4O(COO)6 secondary building unit, has a (3,6)-connected network with an rtl topology and a large solvent cavity.

Topology analysis of metal–organic frameworks based on metal–organic polyhedra as secondary or tertiary building units

The structural features of metal–organic frameworks (MOFs) can be analyzed based on the network structure (net) topology, composed of nodes and linkers. The connectivity and site symmetry of a node are probably the most important factors affecting the net topology of MOFs. Many MOFs with multiple nodes of different connectivity and site symmetry have complicated net topologies. However, the underlying net topology of some complicated MOFs could be analyzed using a hierarchical simplification approach. The underlying net topology of complicated MOFs with multi-connected nodes could be analyzed using a metal–organic polyhedron composed of multiple nodes as either a secondary building unit or a tertiary building unit. The simplified net topology provides better insight into the structural features of the complicated MOF structures and could be utilized in designing new MOF structures with known and/or unprecedented net topologies.

An unprecedented twofold interpenetrated layered metal–organic framework with a MoS2-H topology

An unprecedented twofold interpenetrated layered metal–organic framework with a two-dimensional 3,6-connected net topology has been prepared using a tricarboxylic acid as a 3-connected node and a Zn4O(COO)6 cluster as a 6-connected node, where the ligand flexibility and the combination of π–π stacking and hydrogen bonding interactions render the 6-connected node into a topological trigonal prismatic node.

Isoreticular MOFs based on a rhombic dodecahedral MOP as a tertiary building unit

The solvothermal reactions of a Zn(II) ion with ligands containing two 1,3-benzene dicarboxylate residues linked via bent organic linkers with different flexibilities resulted in the isoreticular metal–organic frameworks (MOFs) PMOF-4 and PMOF-5 based on a rhombic dodecahedral metal–organic polyhedron (MOP) as a tertiary building unit (TBU). The rhombic dodecahedral MOP was built using six [Zn2(COO)4] clusters as a 4-c secondary building unit (SBU) and eight [Zn2(COO)3] clusters as a 3-c SBU. The network of the isoreticular MOFs based on the rhombic dodecahedral Zn–MOP is a 3,3,4-c net with a zjz topology, which is different from those of similar MOFs, PMOF-3 and PCN-12, based on a cuboctahedral Cu–MOP as a 24-c TBU. However, both 24-c TBUs in all MOFs were quadruply interlinked to six neighboring TBUs to form the same underlying pcu topology.