Lu-Yin Zhang

Stepwise Assembly of Pd6(RuL3)8 Nanoscale Rhombododecahedral Metal–Organic Cages via Metalloligand Strategy for Guest Trapping and Protection

Stepwise synthesis of nanosized Pd-Ru heteronuclear metal-organic cages from predesigned redox- and photo-active Ru(II)-metalloligand and naked Pd(II) ion is described. The resulting cage shows rhombododecahedral shape and contains a 5350 Å(3) cavity and 12 open windows, facilitating effective trapping of both polar and nonpolar guest molecules. Protection of photosensitive guests against UV radiation is studied.

Ultrafast water sensing and thermal imaging by a metal-organic framework with switchable luminescence

A convenient, fast and selective water analysis method is highly desirable in industrial and detection processes. Here a robust microporous Zn-MOF (metal–organic framework, Zn(hpi2cf)(DMF)(H2O)) is assembled from a dual-emissive H2hpi2cf (5-(2-(5-fluoro-2-hydroxyphenyl)-4,5-bis(4-fluorophenyl)-1H-imidazol-1-yl)isophthalic acid) ligand that exhibits characteristic excited state intramolecular proton transfer (ESIPT). This Zn-MOF contains amphipathic micropores (<3 Å) and undergoes extremely facile single-crystal-to-single-crystal transformation driven by reversible removal/uptake of coordinating water molecules simply stimulated by dry gas blowing or gentle heating at 70 °C, manifesting an excellent example of dynamic reversible coordination behaviour. The interconversion between the hydrated and dehydrated phases can turn the ligand ESIPT process on or off, resulting in sensitive two-colour photoluminescence switching over cycles. Therefore, this Zn-MOF represents an excellent PL water-sensing material, showing a fast (on the order of seconds) and highly selective response to water on a molecular level. Furthermore, paper or in situ grown ZnO-based sensing films have been fabricated and applied in humidity sensing (RH<1%), detection of traces of water (<0.05% v/v) in various organic solvents, thermal imaging and as a thermometer.

Homochiral D4-symmetric metal-organic cages from stereogenic Ru(II) metalloligands for effective enantioseparation of atropisomeric molecules.

Absolute chiral environments are rare in regular polyhedral and prismatic architectures, but are achievable from self-assembly of metal–organic cages/containers (MOCs), which endow us with a promising ability to imitate natural organization systems to accomplish stereochemical recognition, catalysis and separation. Here we report a general assembly approach to homochiral MOCs with robust chemical viability suitable for various practical applications. A stepwise process for assembly of enantiopure ΔΔΔΔΔΔΔΔ- and ΛΛΛΛΛΛΛΛ-Pd6(RuL3)8 MOCs is accomplished by pre-resolution of the Δ/Λ-Ru-metalloligand precursors. The obtained Pd–Ru bimetallic MOCs feature in large D4-symmetric chiral space imposed by the predetermined Ru(II)-octahedral stereoconfigurations, which are substitutionally inert, stable, water-soluble and are capable of encapsulating a dozen guests per cage. Chiral resolution tests reveal diverse host–guest stereoselectivity towards different chiral molecules, which demonstrate enantioseparation ability for atropisomeric compounds with C2 symmetry. NMR studies indicate a distinctive resolution process depending on guest exchange dynamics, which is differentiable between host–guest diastereomers.

Formation of 0D M5L2 helicate cage and 1D loop-and-chain complexes: stepwise assembly and catalytic activity

The reactions of pyridyl-substituted tripodal ligand 3-TPyMNTB (tris((pyridin-3-ylmethyl)benzimidazol-2-ylmethyl)amine) with Cu(II) chloride give rise to two supramolecular complexes, namely, [Cu5(3-TPyMNTB)2Cl10H2O]·6C3H7NO·11H2O (1), and [Cu5(3-TPyMNTB)2Cl8(H2O)2]Cl2·2CHCl3·2CH2OH (2). The assembly of the two complexes takes place in a stepwise route, including: (1) identical monomeric ML building units are firstly formed in both cases by the coordination of Cu(II) with 3-TPyMNTB using its four central N donors, and (2) the ML units are further linked by the 2-connecting Cu(II) ions through extending pyridyl terminals on the ligands into 0D discrete or 1D infinite structures in complexes 1 and 2, respectively. As a result, 1 presents a unique example of a M5L2 coordination cage which shows a triple helicate shape. Three Bim–Py–Cu(II)–Py–Bim coordination chains constitute the strands of the helicate, which can be outlined by an extending “molecular clip” approach, and such structural character is analyzed in detail in comparison with other known helicate examples. On the other hand, a 1D loop-and-chain structure is formed in complex 2, which can be seen as one strand of the helicate cage in complex 1 being opened up to undergo polymerization. The oxidation catalytic properties of complexes 1 and 2 are tested.

Photoluminescence and white-light emission in two series of heteronuclear Pb(II)–Ln(III) complexes

Two series of Pb(II)–Ln(III) heteronuclear coordination complexes are assembled from a tripodal ligand triCB-NTB ((4,4′,4′′-(2,2′,2′′-nitrilotris(methylene)tris(1H-benzo[d]imidazole-2,1-diyl)tris(methylene))tribenzoic acid)). In the Pb2LnL2 series, the Ln3+ ion is encapsulated in a highly symmetrical {LnO6} octahedron with an inversion center, and Pb–Ln–Pb clusters are formed by the linkage of carboxyl groups on triCB-NTB ligands to Pb2+ and Ln3+ simultaneously. However, in the PbLn2L2 series, the Ln3+ ion is encapsulated in a distorted {LnO9} polyhedron without an inversion center. Pb2+ ions are coordinated with benzimidazole and apical N atoms on the ligand in isolation, and the carboxyl groups link two Ln3+ ions into a Ln–Ln cluster. This structural variation leads to different photoluminescence behaviour in these two series of complexes. Most importantly, the linkage of the Pb–Ln–Pb clusters causes more perturbation to the excited states of the ligand. Therefore, a more obvious ligand-to-metal charge transfer (LMCT) process is observed in the Pb2LnL2 series, and the energy transfer to the accepting levels of Ln3+ ions becomes more efficient. Furthermore, the combination of LC (ligand-centered) + LMCT + MC (metal-centered) emissions in the Pb2EuL2 complex results in single component white light emission.

Semidirected versus holodirected coordination and single-component white light luminescence in Pb(II) complexes

2-Methyl-8-hydroxyquinoline (HMq) and the tripodal ligands 4,4′,4′′-(2,2′,2′′-nitrilotris (methylene)tris(1H-benzo[d]imidazole-2,1-diyl)tris(methylene))tribenzonitrile (triBZ-NTB) and 4,4′,4′′-(2,2′,2′′-nitrilotris(methylene)tris(1H-benzo[d]imidazole-2,1-diyl)tris(methylene))tribenzoic acid (H3triCB-NTB) were used individually to assemble a hetero-nuclear, a tetra-nuclear and two mono-nuclear Pb(II) complexes. The Pb(II) coordination centers in two of these complexes were observed to display semidirected coordination with the ligands and counter anions (small solvent molecules), whereas the other two complexes showed holodirected coordination, together leading to varied coordination geometries. The combination of ligand-to-metal charge-transfer (LMCT) and metal-centered (MC) emissions in the semidirected Pb(II) complexes resulted in single-component white light luminescence.

Time controlled structural/packing transformation and tunable luminescence of Cd(II)-chloride-triBZ-ntb coordination assemblies: an experimental and theoretical exploration

In order to explore the supramolecular solid-state structural and packing transformations and the property tuning as a function of reaction time, a tripodal triBZ-ntb (4,4′,4′′-(2,2′,2′′-nitrilotris(methylene)tris(1H-benzo[d]imidazole-2,1-diyl)tris(methylene))tribenzonitrile) ligand was self-assembled with cadmium chloride by applying a hydrothermal method for differing reaction times. Three coordination structures were obtained, namely, [Cd(triBZ-ntb)Cl]2(CdCl4)·2H2O·2DMF (Cd5), [Cd(triBZ-ntb)Cl2]·3H2O (Cd10), and [Cd(triBZ-ntb)Cl]2(CdCl4)·2H2O (Cd20), and characterized by IR, EA, single crystal and powder X-ray diffraction methods. Cd5 and Cd20 have identical coordination monomers, [Cd(triBZ-ntb)Cl]+ and (CdCl4)2− counter anions, with a total metal-to-ligand ratio of 3 : 2, but with slightly different packing states. Meanwhile, the intermediate compound Cd10 is composed of only a neutral coordination unit [Cd(triBZ-ntb)Cl2], with a metal-to-ligand ratio of 1 : 1, by the additional coordination of one Cl− to the Cd(II) metal center. During the structural transformation process, the formation of (CdCl4)2− counter anions in Cd5 and Cd20 serves as an auxiliary “cabinet” for the storage of surplus Cd2+ metal ions. Theoretical study reveals the relative energy changes in the transformation processes. Furthermore, the switchable structures and packing states in these complexes result in tunable luminescent properties.

Observation of cascade f → d → f energy transfer in sensitizing near-infrared (NIR) lanthanide complexes containing the Ru(II) polypyridine metalloligand

Distinguishable d → f or f → d energy transfer processes depending on lanthanide ions are observed in isomorphous d–f heterometallic complexes containing the Ru(II) metalloligand (LRu), which lead to sensitized NIR emission (for Nd3+ and Yb3+) or enhanced red emission of LRu (for Eu3+ and Tb3+), and represent the first eye-detectable evidence of f → d energy transfer processes in Ln–Ru bimetallic complexes. Based on the systematic luminescence and decay lifetime study, cascade f → d → f energy transfer has been proposed in Ln1–Ru–Ln2 trimetallic systems for improved NIR sensitization.

Binuclear Ru–Ru and Ir–Ru complexes for deep red emission and photocatalytic water reduction

Four butterfly-like binuclear Ru(II)–Ru(II) and Ir(III)–Ru(II) complexes were designed and synthesized via a stepwise method by Ru(II)/Ir(III) metalloligands containing polypyridine (bpy)/phenylpyridine (ppy), phenanthroline (phen) and bibenzimidazole (BiBzIm) moieties. The absorption and photoluminescence of Ru(II)–Ru(II) compounds are dominated by metal-to-ligand charge-transfer (MLCT) transitions from Ru(II) centers to the organic ligand parts, which emit in the deep red region with a wavelength ∼700 nm. While in Ir(III)–Ru(II) complexes, an additional decay channel is opened for the energy transfer from the higher energy level MLCT state of Ir(III)-coordinated units to the lower-energy level MLCT state of Ru(II)-coordinated units, as approved by both experimental and theoretical DFT calculations. Therefore, similar deep red emission profiles originating from Ru(II) units are observed in Ir(III)–Ru(II) systems. These binuclear complexes were further tested as photosensitizers (PSs) to produce H2 in photocatalytic water reduction systems. The highest H2 production efficiency can be obtained in the heteronuclear IrRu(1) system after 80 hours continuous production with a TON value of 1088 based on the amount of IrRu(1) as PS, much higher than the other binunclear complexes and mononuclear counterparts. The results provide a new insight into the designing guidelines for noble metal complexes as emitting centers and photosensitizers in lighting/display materials and devices, as well as photocatalytic water splitting systems.

Dimension Increase via Hierarchical Hydrogen Bonding from Simple Pincer-like Mononuclear complexes.

A tetradentate symmetric ligand bearing both coordination and hydrogen bonding sites, N(1),N(3)-bis(1-(1H-benzimidazol-2-yl)-ethylidene)propane-1,3-diamine (H2bbepd) was utilized to synthesize a series of transition metal complexes, namely [Co(H2bbepd)(H(2)O)2]·2ClO(4) (1), [Cu(H2bbepd)(OTs(-))]·OTs(-) (2),[Cu(bbepd)(CH(3)OH)] (3), [Cd(H(2)bbepd)(NO3)2]·CH(3)OH (4), [Cd(H(2)bbepd)(CH(3)OH)Cl]·Cl (5), and [Cd(bbepd)(CH(3)OH)2] (6). These complexes show similar discrete pincer-like coordination units, possessing different arrangements of hydrogen bonding donor and acceptor sites. With or without the aid of uncoordinated anions and solvent molecules, such mononuclear units have been effectively involved in the construction of hierarchical hydrogen bonding assemblies (successively via level I and level II), leading to discrete binuclear ring (complex 2), one-dimensional chain or ribbon (complexes 3, 4 and 6) and two-dimensional layer (complexes 1 and 5) aggregates.