Heterometallic metal-organic frameworks based on tris(dipyrrinato) coordination complexes

A novel class of heterometallic metal-organic frameworks (MOFs) has been synthesized and characterized. The MOFs rely on the use of tris(dipyrrinato) coordination complexes as the bridging structure and silver(I) ions as the linking unit. The building blocks and resulting MOFs have been structurally characterized by using single-crystal X-ray diffraction. The modular nature of this approach is demonstrated by the use of both iron(III) and cobalt(III) complexes. The MOFs have strong electronic absorption features originating from the metal-dipyrrin chromophore and have continuous channels throughout the lattice that are occupied by ordered and disordered solvent molecules.     

Different two-dimensional metal-organic frameworks through ligand modification

Through ligand modification, we have replaced the central benzene ring of H₂TDBA ([1,1′:3′,1″-terphenyl]-4,4″-dicarboxylic acid) with the pyridine structurally related ligand H₂PDDA (4,4′-(pyridine-2,6-diyl)dibenzoic acid), which makes the central pyridine ring of H₂PDDA more coplanar with two benzene rings on both sides of the ligand. The modification results in a dramatically different linkage configuration, thereby allowing structural changes to the metal-organic frameworks (MOFs). Two 2-D MOFs, [Cu(TDBA)(DMA)₂]·H₂O (BUT-221, DMA = N,N-dimethylacetamide), and [Cu₃(PDDA)₃(DMA)₂(H₂O)]·5H₂O (BUT-223) have been synthesized through reactions of two ditopic carboxylate ligands with Cu(NO₃)₂·3H₂O under solvothermal conditions, and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. Topological analysis shows that BUT-221 is a twofold parallel interpenetrating 4⁴ 2-D network with a skl topology, while BUT-223 is a 2-D network with a kgm topology.     

Extended coordination frameworks incorporating heterobimetallic squares

The molecular structure of aluminium and iron(III) complexes with 3-phenyl and 3-(4-pyridyl) (HL) substituted acetylacetonate ligands is appreciably distorted. For AlL3 and FeL3 this shows that the orientation of the side pyridyl-N donor atoms lone pairs is about 90 and 135 degrees which favours the assembly of heterobimetallic square patterns in Al(Fe)L3 complexes with metal ions. This was employed for the modular construction of semi-regular heterobimetallic networks, in which the pyridyldiketonate ligands bridge pairs of Fe(Al)/Cd(Co) metal ions and support the structure of 1D and 2D coordination polymers. The unprecedented 2D structure of [Cd[AlL3](CH3OH)[NO3]2].2CHCl3 and Cd[AlL3](CH3OH)Br2].2CHCl3 . 2CH3OH is based upon plane tiling by a set of heterobimetallic squares and octagons, while [Cd[FeL3]2(NO3)2].2H2O and [Co[AlL3]2Cl2].4CHCl3 . 2CH3OH are 1D polymers and exist as chains of heterobimetallic squares sharing opposite vertices.     

Novel one-dimensional tubelike and two-dimensional polycatenated metal-organic frameworks

Two novel metal-organic frameworks (MOFs) [Zn(TITMB)(OAc)](OH).8.5H(2)O (1) and [Ag(TITMB)N(3)].H(2)O (2) [TITMB = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, OAc = acetate anion] were synthesized and their structures were determined by X-ray crystallography. Complex 1 crystallizes in tetragonal space group P(-)4 with a = 23.2664(7) and c = 11.9890(3) A and Z = 8. 1 has a one-dimensional tubelike structure with large inner pore size of approximately 17 A. Complex 2 crystallizes in monoclinic space group C2 with a = 20.7193(10), b = 11.5677(8), and c = 12.2944(6) A, beta = 125.5770(10) degrees, and Z = 4. 2 consists of two-dimensional honeycomb networks that interpenetrate each other to generate a polycatenated structure. In these two complexes, both zinc(II) and silver(I) atoms are four-coordinated with the same tetrahedral coordination geometry. The topologies of 1 and 2 are predominated by the conformations of TITMB, which are cis, trans, trans in 1 and cis, cis, cis in 2, respectively.     

Surface-template assembly of two-dimensional metal-organic coordination networks

The self-assembly of iron-coordinated two-dimensional metal-organic networks on a Cu(100) surface has been investigated by scanning tunneling microscopy under ultra-high-vacuum conditions. We applied three rodlike polybenzene dicarboxylic acid molecules with different backbone lengths as organic linkers. The three linker molecules form topologically identical rectangular networks with Fe, all comprising iron pairs as the network nodes. Whereas the length of the linker molecules defines the dimension of the networks, the substrate also significantly influences the structural details, e.g., network orientation with respect to the substrate, geometric shape of the network cavities, Fe-carboxylate coordination configuration, and iron-iron distance.     

Highly adaptable two-dimensional metal-organic coordination networks on metal surfaces

The formation of extended two-dimensional metal-organic coordination networks (2D-MOCNs) showing high adaptability to surface step edges and structural defects is revealed by scanning tunneling microscopy. Rod-like 4,4'-di-(1,4-buta-1,3-diynyl)-benzoic acid (BDBA) and iron atoms assemble into extended 2D-MOCNs on Au(111) and Ag(100) surfaces. Independent from the chosen substrate and its surface symmetry the MOCN grows continuously over multiple surface terraces through mutual in-phase structure adaptation of network domains at step edges as well as on terraces. The adaptability of the MOCNs is mainly ascribed to the high degree of conformational flexibility of the butadiynyl functionality of the ligand. Despite their flexibility, the MOCNs exhibit considerable robustness against annealing at high temperatures. The findings show that mesoscale self-assembled functional architectures with a high degree of substrate error tolerance can be realized with metal coordination networks.     

Functional tetrametallic linker modules for coordination polymers and metal-organic frameworks

The new biphenol-based tetranucleating ligand, 2,2',6,6'-tetrakis(N,N-bis(2-pyridylmethyl)aminomethyl)-4,4'-biphenolate, dbpbp2-, comprises two linearly disposed phenolato-hinged dinucleating heptadentate units, each of which offer one O and three N donors to a total of four metal ions. The ligand has been isolated as the zinc chloride complex [Zn4(dbpbp)Cl4]2+, and the ZnII ions have been completely or partially substituted by CuII, FeIII, CoII, and CoIII in metathesis reactions. Similarly, the chloride ligands of [Zn4(dbpbp)Cl4]2+ have been exchanged for solvent molecules (acetonitrile and/or water) and bridging carboxylate ligands. The resulting complexes have been characterized by single-crystal X-ray diffraction, ESI mass spectrometry (ESI-MS), cyclic voltammetry (CV), and EPR spectroscopy. The structures containing [M4(dbpbp)Cl4]2+ with M = ZnII or CuII exhibit 2-D polymeric honeycomb sheets in which intermolecular M...Cl interactions bridge between adjacent [M4(dbpbp)Cl4]2+ cations. Two mixed-metal tetrabenzoate complexes [M4(dbpbp)(O2CC6H5)4]2+/3+ have also been prepared, namely a stoichiometric CuII2ZnII2 complex and a nonstoichiometric FeIII/ZnII system. In the latter case, ESI-MS identifies FeZn3, Fe2Zn2, and Zn4 species, and X-ray crystallography suggests an average composition of Fe0.8Zn3.2. Preparation of a CoII4 complex by metathesis was considerably more difficult than preparation of [Cu4(dbpbp)Cl4]2+, requiring both a large excess of the cobalt source and the presence of auxiliary benzoate. In the presence of 2 equiv of benzoate per starting [Zn4(dbpbp)Cl4]2+ unit and excess CoII, dioxygen binds as peroxide at each end of the molecule to give the CoIII4 complex [Co4(dbpbp)(O2)2(O2CC6H5)2]4+. This latter complex, together with new tetra- and hexametallic benzenedicarboxylato- and benzenetricarboxylato-bridged complexes of dinuclear [Co2(O2)(bpbp)]3+ units (bpbp- = 2,6-bis(N,N-bis-(2-pyridylmethyl)aminomethyl)-4-tert-butyl-phenolate), is a module for potential construction of 1-D and 2-D coordination polymers/metal-organic frameworks (MOFs) capable of reversible O2 binding.     

Gyroidal metal-organic frameworks

The gyroid is ubiquitous for underlying the construction of natural substance and artificial zeolites, but it has been, surprisingly, overlooked by chemists who work in the field of metal-organic frameworks (MOFs). In this work, a series of gyroidal MOFs with gie topology, constructed from 1,2-bis((5H-imidazol-4-yl)methylene)hydrazine and octahedral metal ions, such as Zn(II), Mn(II), Cu(II), and Ni(II), have been synthesized. The Zn(II) analogue, named as STU-1, shows exceptional thermal and chemical stabilities, and exhibits permanent porosity and CO(2) capture ability.     

Liquid-phase adsorption on metal-organic frameworks

This work is focusing on the potential application of metal-organic frameworks as porous materials in heterogeneous catalysis where the substrate is in solution. The understanding of such a liquid-phase heterogeneous catalytic process requires adsorption equilibrium data in solution. For this purpose several metal-organic frameworks were synthesized as reference materials and tested as adsorbents for the adsorption of substrate molecules such as styrene or ethylcinnamate from the liquid phase. The adsorption capacity strongly depends on the polarity of the substrate with respect to the solvent. In several instances solvent and polarity effects are heavily superimposed on the pore size effects. Adsorption isotherms, rates and hydrogenation of the substrates are reported and discussed.     

Multi-functional sites catalysts based on post-synthetic modification of metal-organic frameworks

Multi-functional sites MOFs have been explored as a new type of heterogeneous catalytic materials, which can be constructed by various post-synthetic modifications.     

Luminescent zinc and cadmium metal-organic frameworks based on tetrazole ligands

Three metal-organic frameworks with 1D zigzag chain [Zn(dte)(H₂O)₃]·2H₂O (1), 2D double layer [Cd(dtb)(H₂O)(phen)] (2), 3D network [Zn(dte)(phen)] (3) based on tetrazole-based ligands (H₂dtb = 1,3-dis(2H-tetrazol-5-yl)benzene, H₂dte = 1,4-ditetrazolylethylene, phen = 1,10-phenanthroline), have been synthesized and characterized. All the compounds exhibit unusual strong luminescence at room temperature in the solid state and can be potentially used as luminescent materials.     

Extended metal-organic solids based on benzenepolycarboxylic and aminobenzoic acids

This article describes the recent results obtained in our laboratory on the interaction of polyfunctional ligands with divalent alkaline earth metal ions and a few divalent transition metal ions. Treatment of MC1₂·nH₂O (M = Mg, Ca, Sr or Ba) with 2-amino benzoic acid leads to the formation of complexes [Mg(2-aba)₂] (1), [Ca(2-aba)₂(OH₂)₃]∞ (2), [Sr(2-aba)₂(OH₂)_{2 2}·H₂O)]∞ (3), [Ba(2-aba)₂(OH₂)]∞ (4), respectively. While the calcium ions in2 are hepta-coordinated, the strontium and barium ions in3 and4 reveal a coordination number of nine apart from additional metal-metal interactions. Apart from the carboxylate functionality, the amino group also binds to the metal centres in the case of strontium and barium complexes3 and4. Complexes [Mg(H₂O)₆(4-aba)₂·2H₂O] (5), [Ca(4-aba)₂(H₂O)₂] (6) prepared from 4-aminobenzoic acid reveal more open or layered structures. Interaction of 2-mercaptobenzoic acid with MCl₂·6H₂O (M = Mg, Ca), however, leads to the oxidation of the thiol group resulting in the disulphide 2,2′ -dithiobis(benzoic acid). New metal-organic framework based hydrogen-bonded porous solids [M(btec) (OH₂)_{4 n}·n(C₄H₁₂N₂)·4nH₂O] (btec = 1,2,4,5-benzene tetracarboxylate) (M = Co9; Ni10; Zn11) have been synthesized from 1,2,4,5-benzene tetracarboxylic acid in the presence of piperazine. These compounds are made up of extensively hydrogen-bonded alternating layers of anionic M-btec co-ordination polymer and piperazinium cations. Compounds2- 11 described herein form polymeric networks in the solid-state with the aid of different coordinating capabilities of the carboxylate anions hydrogen bonding interactions.     

Nanoporous carbohydrate metal-organic frameworks

The binding of alkali and alkaline earth metal cations by macrocyclic and diazamacrobicyclic polyethers, composed of ordered arrays of hard oxygen (and nitrogen) donor atoms, underpinned the development of host-guest supramolecular chemistry in the 1970s and 1980s. The arrangement of -OCCO- and -OCCN- chelating units in these preorganized receptors, including, but not limited to, crown ethers and cryptands, is responsible for the very high binding constants observed for their complexes with Group IA and IIA cations. The cyclodextrins (CDs), cyclic oligosaccharides derived microbiologically from starch, also display this -OCCO- bidentate motif on both their primary and secondary faces. The self-assembly, in aqueous alcohol, of infinite networks of extended structures, which have been termed CD-MOFs, wherein γ-cyclodextrin (γ-CD) is linked by coordination to Group IA and IIA metal cations to form metal-organic frameworks (MOFs), is reported. CD-MOF-1 and CD-MOF-2, prepared on the gram-scale from KOH and RbOH, respectively, form body-centered cubic arrangements of (γ-CD)(6) cubes linked by eight-coordinate alkali metal cations. These cubic CD-MOFs are (i) stable to the removal of solvents, (ii) permanently porous, with surface areas of ~1200 m(2) g(-1), and (iii) capable of storing gases and small molecules within their pores. The fact that the -OCCO- moieties of γ-CD are not prearranged in a manner conducive to encapsulating single metal cations has led to our isolating other infinite frameworks, with different topologies, from salts of Na(+), Cs(+), and Sr(2+). This lack of preorganization is expressed emphatically in the case of Cs(+), where two polymorphs assemble under identical conditions. CD-MOF-3 has the cubic topology observed for CD-MOFs 1 and 2, while CD-MOF-4 displays a channel structure wherein γ-CD tori are perfectly stacked in one dimension in a manner reminiscent of the structures of some γ-CD solvates, but with added crystal stability imparted by metal-ion coordination. These new MOFs demonstrate that the CDs can indeed function as ligands for alkali and alkaline earth metal cations in a manner similar to that found with crown ethers. These inexpensive, green, nanoporous materials exhibit absorption properties which make them realistic candidates for commercial development, not least of all because edible derivatives, fit for human consumption, can be prepared entirely from food-grade ingredients.     

3D coordination metal-organic frameworks of octacyanometalate bridging between Cu4 magnetic units

Magnetic Cu4 clusters with S = 2 are bridged by octacyanometaltate(IV) to form two 3D cluster arrays of metal-organic frameworks. Magnetic investigation shows the ferromagnetic coupling between Cu(II) ions and very weak antiferromagnetic interaction between clusters.     

Assembly of the first fullerene-type metal-organic frameworks using a planar five-fold coordination node

Pump up the volume: Slow crystallization of Na[C(5) (CN)(5) ], the unsolvated sodium salt of pentacyanocyclopentadienide, gives the first example of an anionic coordination network based on metal-fullerene units. The structure of this network is closely related to a type?I gas clathrate in which around 66?% of the unit cell volume is occupied by solvent molecules.     

金属有机框架材料的研究进展

金属有机框架(metal-organic frameworks,MOFs)材料是一类由有机配体与金属中心经过自组装形成的具有可调节孔径的材料。与传统无机多孔材料相比,MOFs材料具有更大的比表面积,更高的孔隙率,结构及功能更加多样,因而已经被广泛应用于气体吸附与分离、传感器、药物缓释、催化反应等领域中。新兴材料的出现极大地促进了各个学科间的相互发展,本文综述了近年来MOFs材料的研究发展,包括MOFs材料自身的特点、国内外发展现状、应用领域以及复合MOFs材料的研究热点,并对今后的发展进行了展望。     

Influence of temperature on metal-organic frameworks

Reaction temperature is one of the key parameters in the synthesis of metal-organic frameworks （MOFs）. Though there is no convergence with regard to the various experimental parameters, reaction temperature has been found to have remarkable influence on the formation and structure of MOFs, especially toward the control of topology and dimensionality of the MOF structures. Theoretically, the reaction temperature affects directly the reaction energy barrier in reaction thermodynamics and the reaction rate in the reaction kinetics. This review aims to show the influence of reaction temperature on crystal growth/assembly, structural modulation and transformation of MOFs, and to provide primary information and insights into the design and assernblv of desired MOFs.