Huabin Zhang

A multi-metal-cluster MOF with Cu4I4 and Cu6S6 as functional groups exhibiting dual emission with both thermochromic and near-IR character

Two classical metal clusters, CuI4I4 and CuI6S6, are introduced as functional connecting nodes to construct a novel multi-metal-cluster MOF [(CuI4I4)3(CuI6)2(3-ptt)12]n·24nDEF·12nH2O (1) that incorporate their inherent luminescent properties, induced by their respective metal–metal interactions. These two distinct clusters are combined together for the first time to perform as functional luminophores that display unusual dual emission with both thermochromic luminescence and near-infrared (NIR) character.

Full-colour fluorescent materials based on mixed-lanthanide(III) metal–organic complexes with high-efficiency white light emission

In this communication, we report a series of high-efficiency full-colour fluorescent materials based on isostructural mixed-lanthanide metal–organic complexes. By varying the stoichiometric ratio of the lanthanide ions, a fluent change of emission colours within the full-colour region was realized and strong white light-emission with a high quantum yield up to 62% was also achieved.

Highly luminescent and thermostable lanthanide-carboxylate framework materials with helical configurations†

New luminescent lanthanide-carboxylate frameworks, formulated as [Ln4(m-BDC)6(H2O)4(DMF)]·(H2O)2·(DMF) (Ln = Eu 1; Gd 2; Tb 3) (m-H2BDC = 1,3-benzenedicarboxylic acid) have been solvo(hydro)thermally synthesized. Single-crystal X-ray diffraction studies reveal that compounds 1–3 are isomorphous and each displays a layered structure constructed by helical lanthanide-carboxylate chains. DFT and TD-DFT calculations were conducted in detail to discuss the energy levels, including the HOMO, LUMO, singlet and triplet energies of the m-H2BDC ligand. The results indicate that the m-BDC2− dianion acts as an antenna chromophore that is able to efficiently absorb and transfer energy to the lanthanide ions. Compounds 1–3 all exhibit high thermostability and are stable up to 450 °C, as confirmed by the TGA and temperature-dependent PXRD experiments. Compounds 1 and 3 are strong luminescent materials. Compound 3 is among some of the best examples of luminescent lanthanide compounds, with highly efficient emission quantum yields of 81.40% at 77 K, 75.37% at room temperature and 56.64% after calcination at 450 °C, respectively. In addition, the energy transfer processes for compounds 1 and 3 have also been studied and illustrated in detail.

A highly luminescent chameleon: fine-tuned emission trajectory and controllable energy transfer

By varying the stoichiometric ratio of Eu3+, Tb3+ and Gd3+ ions in a lanthanide metal–organic framework, a mixed-Ln MOF, [Eu0.0040Tb0.0460Gd0.9500(BTB)(DMSO)2]·H2O, has been designed to display white-light emission. In addition, the switch between blue, white, and yellow for this material has been achieved by controlling the energy transfer process.

Tunable luminescence and white light emission of mixed lanthanide–organic frameworks based on polycarboxylate ligands

In the last few years, Ln-MOFs, which are stable multi-dimensional frameworks composed of highly luminescent Ln3+ ions and multitopic organic ligands, have become a very fascinating class of materials in view of their luminescence properties. Their luminescence can be easily modulated owing to their structural diversity and predictability, as well as multiple options for excitation and emission, including those performed via the organic linker serving as an efficient antenna, the discrete energy levels of Ln3+ ions, and the luminescent guests that were trapped in the cavities. In particular, the similarity in the chemical reactivity and the coordination environment of different Ln3+ ions allows the formation of a series of isostructural mixed Ln-MOFs whose colour output can be fine-tuned by changing the types and relative concentration of the constituent Ln3+ ions or the excitation wavelength. Most significantly, white-light emitting materials may be obtained if the mixing of Ln3+ ions can be carefully controlled. Based on these unique properties, mixed Ln-MOFs may play an outstanding role in the fields of lighting and display systems. The aim of this review is to provide an overview of the current status of the research on mixed Ln-MOFs, especially those constructed using aromatic polycarboxylate ligands, and to highlight their colour tunable and white light emission properties.

An alternative strategy to construct Fe(II)-based MOFs with multifarious structures and magnetic behaviors

An alternative strategy using cyclopentadienyliron dicarbonyl dimer as a starting material has been applied to construct six new Fe(II)-based MOFs, formulated as [Fe2(Nic)4(μ-H2O)]·CH3CN (1), [Fe(PIP)(H2O)]·H2O (2), [Fe(Hbidc)(H2O)] (3), [Fe(Hbidc)] (4), [Fe(Py-3,4-BDC)(H2O)2]·H2O (5) and [Fe(Py-3,4-BDC)(H2O)2] (6) (HNic = nicotinic acid, H2PIP = 5-(pyridin-4-yl) isophthalic acid, H3bidc = benzimidazole-5,6-dicarboxylic acid and Py-3,4-H2BDC = 3,4-pyridinedicarboxylic acid). X-ray structural analysis reveals that 1 possesses a 3D framework, while the rest of the compounds are 2D layer structures which are further connected by hydrogen bonding into 3D supramolecular architectures. Magnetic analyses have been performed with the classical spin approximation, revealing that 2, 5 and 6 exhibit ferromagnetic interactions between Fe(II) ions, while 3 and 4 show antiferromagnetic interactions between Fe(II) centres. The successful preparation of compounds 1–6 may provide an alternative and useful approach for the synthesis of Fe(II)-based MOFs in the future.

Two enantiomorphic 3D Zn(II)–carboxylate MOFs with double helical structures serving as a chiral source induced by hydrogen bonding

Two enantiomorphic 3D Zn(II)–carboxylate metal–organic frameworks [Zn(bpydc)(H2O)2] (1M and 1P) (H2bpydc = 2,2′-bipyridyl-5,5′-dicarboxylic acid) have been synthesized. They both contain an elegant double helix, self-organized through hydrogen bonds between the coordinated water molecules and uncoordinated carboxylate oxygen atoms. This double helical structure serves as a chiral source which transmits chiral information over the whole 3D framework.

Synthesis, structures and luminescent properties of new Pb(II)/M(I) (M = K, Rb and Cs) frameworks based on dicarboxylic acids: a novel icosahedral Pb6-M6 SBU

Reactions of Pb(CH3COO)2·3H2O, MNO3 (M = K, Rb, and Cs) with m-H2BDC (1,3-H2BDC = 1,3-benzenedicarboxylic acid) in a mixed-solvent of DMF and methanol (v/v = 2/1) resulted in the formation of novel metal–organic frameworks [(Me)4N]2[Pb6M6(m-BDC)9(OH)2]·H2O (1: M = K; 2: M = Rb; 3: M = Cs). With H2SDBA (H2SDBA = 4,4′-sulfonyldibenzoic acid), two new lead(II) coordination polymers, [K2Pb(SDBA)2(μ3–H2O)]·3H2O (4) and [Cs2Pb2(SDBA)3(DMF)] DMF (5), were isolated. These complexes have been fully characterized by elemental analysis, PXRD, FTIR, TGA and single crystal X-ray diffraction. Compounds 1–3 are 3-D coordination frameworks built by a novel 12-metal heterometallic Pb6-M6 cage that extends topologically into an eight-connected hex network viaisophthalic acid ligands. Compounds 4 and 5 are new 3-D lead(II) MOFs constructed by ladder-like Pb(II)/K(I)/SDBA2− and rod-shaped Pb(II)/Cs(I)/SDBA2− motifs, respectively. The Pb(II) ions in these complexes show different coordination geometries with various coordination numbers (5, 7 and 9). In addition, an ideal T-shaped μ3-H2O is observed in 4. The SDBA2− ligands in 4 and 5 display three types of new coordination modes that have not been observed before. At room temperature, 1–3 exhibit strong emissions in the solid-state which can be attributed to ligand-to-metal charge transfer between the delocalized π bonds of carboxylate groups and p orbitals of lead(II) centers.

Acentric and chiral heterometallic inorganic–organic hybrid frameworks mediated by alkali or alkaline earth ions: synthesis and NLO properties

The rapid development in inorganic–organic hybrid frameworks has enabled the discovery of many structurally fascinating and technologically useful materials. The design of such hybrid crystals with noncentrosymmetric frameworks is particularly important because of their interesting electronic and optical properties. Several synthetic approaches, including the use of chiral and unsymmetric ligands, or spontaneous resolution via using achiral building blocks, have been applied to facilitate the formation of acentric and chiral hybrid materials. In this highlight, we will review another way to increase the chance of obtaining acentric and chiral frameworks by adding alkali or alkaline earth metals into heterometallic systems. The synthesis of these frameworks is discussed along with their potential NLO properties.

Interweaving of two enantiomorphic 3D Cd(II)/K(I) coordination polymers with homochiral unequal triple concentric helical chains

The solvothermal reaction of Cd(NO3)2·4H2O and KNO3 with 1,3-benzenedicarboxylic acid (m-H2BDC) in the presence of D- or L-2-amino-1-propanol (D- or L-APA) in ethanol led to two enantiomorphic Cd(II)/K(I) coordination polymers, namely [Cd3K3(D-HAPA)3(m-BDC)6(EtOH)3]n (1D) and [Cd3K3(L-HAPA)3(m-BDC)6(EtOH)3]n (1L). They are 3D coordination polymers with multi-walled tubular channels constructed from a novel homochiral triple concentric helical structure in which a single helix {CdK–BDC}n is wrapped by unequal double-helical chains {Cd–BDC}n. Both complexes are NLO-active with weak SHG efficiencies.