Qi-Bing Bo

Structure and Photoluminescence Tuning Features of Mn2+- and Ln3+-Activated Zn-Based Heterometal–Organic Frameworks (MOFs) with a Single 5-Methylisophthalic Acid Ligand

In attempts to investigate whether the photoluminescence properties of the Zn-based heterometal-organic frameworks (MOFs) could be tuned by doping different Ln(3+) (Ln = Sm, Eu, Tb) and Mn(2+) ions, seven novel 3D homo- and hetero-MOFs with a rich variety of network topologies, namely, [Zn(mip)](n) (Zn-Zn), [Zn(2)Mn(OH)(2)(mip)(2)](n) (Zn-Mn), [Mn(2)Mn(OH)(2)(mip)(2)](n) (Mn-Mn), [ZnSm(OH)(mip)(2)](n) (Zn-Sm), [ZnEu(OH)(mip)(2)](n) (Zn-Eu1), [Zn(5)Eu(OH)(H(2)O)(3)(mip)(6)·(H(2)O)](n) (Zn-Eu2), and [Zn(5)Tb(OH)(H(2)O)(3)(mip)(6)](n) (Zn-Tb), (mip = 5-methylisophthalate dianion), have been synthesized hydrothermally based on a single 5-methylisophthalic acid ligand. All compounds are fully structurally characterized by elemental analysis, FT-IR spectroscopy, TG-DTA analysis, single-crystal X-ray diffraction, and X-ray powder diffraction (XRPD) techniques. The various connectivity modes of the mip linkers generate four types of different structures. Type I (Zn-Zn) is a 3D homo-MOF with helical channels composed of Zn(2)(COO)(4) SBUs (second building units). Type II (Zn-Mn and Mn-Mn) displays a nest-like 3D homo- or hetero-MOF featuring window-shaped helical channels composed of Zn(4)Mn(2)(OH)(4)(COO)(8) or Mn(4)Mn(2)(OH)(4)(COO)(8) SBUs. Type III (Zn-Sm and Zn-Eu1) presents a complicated corbeil-like 3D hetero-MOF with irregular helical channels composed of (SmZnO)(2)(COO)(8) or (EuZnO)(2)(COO)(8) heterometallic SBUs. Type IV (Zn-Eu2 and Zn-Tb) contains a heterometallic SBU Zn(5)Eu(OH)(COO)(12) or Zn(5)Tb(OH)(COO)(12), which results in a 3D hetero-MOF featuring irregular channels impregnated by parts of the free and coordinated water molecules. Photoluminescence properties indicate that all of the compounds exhibit photoluminescence in the solid state at room temperature. Compared with a broad emission band at ca. 475 nm (λ(ex) = 380 nm) for Zn-Zn, compound Zn-Mn exhibits a remarkably intense emission band centered at 737 nm (λ(ex) = 320 nm) due to the characteristic emission of Mn(2+). In addition, the fluorescence intensity of compound Zn-Mn is stronger than that of Mn-Mn as a result of Zn(2+) behaving as an activator for the Mn(2+) emission. Compound Zn-Sm displays a typical Sm(3+) emission spectrum, and the peak at 596 nm is the strongest one (λ(ex) = 310 nm). Both Zn-Eu1 and Zn-Eu2 give the characteristic emission transitions of the Eu(3+) ions (λ(ex) = 310 nm). Thanks to the ambient different crystal-field strengths, crystal field symmetries, and coordinated bonds of the Eu(3+) ions in compounds Zn-Eu1 and Zn-Eu2, the spectrum of the former compound is dominated by the (5)D(0) → (7)F(2) transition (612 nm), while the emission of the (5)D(0) → (7)F(4) transition (699 nm) for the latter one is the most intense. Compound Zn-Tb emits the characteristic Tb(3+) ion spectrum dominated by the (5)D(4) → (7)F(5) (544 nm) transition. Upon addition of the different activated ions, the luminescence lifetimes of the compounds are also changed from the nanosecond (Zn-Zn) to the microsecond (Zn-Mn, Mn-Mn, and Zn-Sm) and millisecond (Zn-Eu1, Zn-Eu2, and Zn-Tb) magnitude orders. The structure and photoluminescent property correlations suggest that the presence of Mn(2+) and Ln(3+) ions can activate the Zn-based hetero-MOFs to emit the tunable photoluminescence.

A new family of 3D 3d–4f heterometallic frameworks comprising 1D inorganic lanthanide ladders and organic CuI-bipyridine chains

A new family of the 3D heterometallic coordination polymers [{Ln2(SO4)2(H2O)2(pydc)2Cu2 (bpy)2·2(H2O)}]n (Ln = Sm (1), Eu (2), Gd (3), Tb (4) and Dy (5); pydc = 2,6-pyridine-dicarboxylate anion; bpy= 4,4′-bipyridine) have successfully been synthesized under solvothermal conditions (H2O/ethanol). All the coordination polymers obtained were characterized by elemental analysis, FT-IR analysis, differential thermal analysis/thermogravimetry (DTA/TG), fluorescent spectra and single crystal X-ray diffraction analysis. The most intriguing structural feature is that all the compounds exhibit 3D frameworks with 1D inorganic lanthanide ladders and organic CuI-bipyridine chains, which represent two types of 3d/4f coordination polymers (form I: Ln = Sm and Eu; form II: Ln = Gd, Tb and Dy) as the result of a so-called “gadolinium break effect”. Additionally, compounds 2 and 4 showed the characteristic emission spectra of the EuIII and TbIII ions, respectively, and appeared to have good fluorescence properties, while 1, 3 and 5 emitted fluorescence resembling CuI complexes. To our knowledge, the investigation of the effect of mixed ligands on the assembly of LnIII-CuI metal-based polymers has not been reported so far.

Synthesis, characterization and photoluminescent properties of Zn-based mono- and hetero-MOFs containing the R-isophthalate (R = methyl or tert-butyl) ligands

Four novel Zn-based homo- and hetero-metal organic frameworks (MOFs), [Zn2(H2O)(mip)2]n (Zn-mip), [ZnMg(H2O)2(mip)2·3(H2O)]n (ZnMg-mip), [Zn3(OH)2(tbip)2]n (Zn-tbip) and [Zn2Ba(O)(H2O)2(tbip)2.5·(H2O)]n (ZnBa-tbip), have been hydrothermally synthesized by employing the single ligand 5-methyl isophthalic acid (H2mip) or 5-tert-butyl isophthalic acid (H2tbip). The structures of all the MOFs are determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, inductively coupled plasma (ICP) analysis, FT-IR spectroscopy, DTA/TG analyses and X-ray powder diffraction (XRPD) techniques. The results indicate that all the homo- and hetero-MOFs exhibit the 3D open frameworks with the unique Zn-based cluster second building units (SBUs). The influence of the coordination geometries of the hetero-metal centers on the structures of Zn-based mono-MOFs is realized through replacing the five (or four)-coordinated Zn atoms with the alkaline-earth metal ions. Moreover, compared with the free ligands, the photoluminescent properties of the Zn-mip, ZnMg-mip, Zn-tbip and ZnBa-tbip are also studied in the solid state at room temperature. The different emission bands of the homo- and hetero-MOFs demonstrate that the substituent effect of alkaline-earth metal ions plays a key role in directing the related photoluminescent properties of the Zn-based MOFs.

New Family of Octagonal-Prismatic Lanthanide Coordination Cages Assembled from Unique Ln17 Clusters and Simple Cliplike Dicarboxylate Ligands

Novel high-nuclearity lanthanide clusters (Ln17) are generated in situ in the coordination-driven self-assembly. A metal-cluster-directed symmetry strategy for building metal coordination cages is successfully applied to a lanthanide system for the first time. A new family of octagonal-prismatic lanthanide coordination cages UJN-Ln, formulated as [Ln(μ3-OH)8][Ln16(μ4-O)(μ4-OH)(μ3-OH)8(H2O)8(μ4-dcd)8][(μ3-dcd)8]·22H2O (Ln = Gd, Tb, Dy, Ho, and Er; dcd = 3,3-dimethylcyclopropane-1,2-dicarboxylate dianion), have been assembled from the unique Ln17 clusters and simple cliplike ligand H2dcd. Apart from featuring aesthetically charming structures, all of the compounds present predominantly antiferromagnetic coupling between the corresponding lanthanide ions. Additionally, the intense-green photoluminescence for UJN-Tb and magnetic relaxation behavior for UJN-Dy have been observed. Remarkably, UJN-Gd shows a large magnetocaloric effect (MCE) with an impressive entropy change value of 42.3 J kg(-1) K(-1) for ΔH = 7.0 T at 2.0 K due to the high-nuclearity cluster and the lightweight ligand. The studies highlight the structural diversity of multigonal-prismatic metal coordination cages and provide a new direction in the design of cagelike multifunctional materials by the introduction of lanthanide clusters and other suitable cliplike ligands.

Fluorescent Zn-based hetero-MOFs design via single metal site substitution

Two pairs of novel Zn-based MOFs with the same structures are synthesized. The exchange mechanism between the primary MOFs and the substituted MOFs is discussed. The utilization of the single metal site substitution in pre-formed Zn-based MOFs appears suited to the design of isostructural Zn-based hetero-MOFs with different photoluminescence properties.

Novel metal–organic frameworks (MOFs) based on heterometallic nodes and 5-methylisophthalate linkers

Based on 5-methylisophthalate organic linkers, two novel metal–organic frameworks (MOFs) have been assembled from Zn2Na(COO)6 and Zn5K(COO)12 secondary building units (SBUs), which contain 3D anionic frameworks with 1D nanotubular helical channels replete with hydrated alkali metal cation clusters.

In situ solvent and counteranion-induced synthesis, structural characterization and photoluminescence properties of Pb-based MOFs

Based on an attempt to investigate the influence of solvents and counteranions on the structures and photoluminescence properties of Pb-based metal–organic frameworks, the hydrothermal reactions of the same amounts of Pb(NO3)2 and Pb(OAc)2 with the ligand 5-tert-butylisophthalic acid (H2tip) in the presence of water and a water–ethanol mixture have yielded three compounds [Pb(H2O)(tip)]n (1), [Pb3(μ4-O)(tip)2]n (2) and [Pb4(μ4-O)(tip)3]n (3) under similar reaction conditions (tip = 5-tert-butylisophthalate anion). These compounds represented the first examples of Pb(II) metal–organic frameworks with H2tip. All of them have been characterized by means of FT-IR spectra, elemental analysis, single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, and photoluminescence spectra. The reaction processes revealed that 1 and 2 had selectivity for specific solvents. And the selectivity for specific counteranions was also found in 2 and 3. Single-crystal X-ray diffraction showed that 1 and 3 crystallized in the orthorhombic crystal system with space groups of Iba2 and Pna21, respectively, while 2 crystallized in the monoclinic P21/c space group. The structure of 1 featured a 2D bilayer structure containing a uninodal sql-type topological motif with a Schlafli symbol of (44). The 2D layer framework of 2 was constructed from a unique 8-connected hexanuclear cluster secondary building unit Pb6O2(COO)8, resulting in a uninodal hxl-type topological motif with a Schlafli symbol of (36·46·53). The structure of 3 could be described as a 3D microporous framework with a 6-connected tetranuclear cluster Pb4O(COO)6. Topological analysis revealed that 3 represented a uninodal dia-type topological motif with a Schlafli symbol of (66). All of the solid state compounds exhibited the photoluminescence properties at room temperature. Furthermore, taking the emissions of the free ligand into consideration, the emissions 1 and 2 could be assigned to metal-centered s → p transition transitions, while the emissions of 3 were due to ligand-to-metal charge transfers between the delocalized p bonds of carboxylate groups and p orbitals of Pb(II) centers. Especially, the in situ solvent and counteranion-induced synthesis strategy reported here could afford us new opportunities in the rapid design of new materials with interesting structures and properties.

CCDC 822110: Experimental Crystal Structure Determination

Related Article: Qi-Bing Bo, Hong-Yan Wang, Da-Qi Wang, Zhen-Wei Zhang, Jin-Ling Miao, Guo-Xin Sun|2011|Inorg.Chem.|50|10163|doi:10.1021/ic201124c