Zinc–dipyridylanthracene–based metal–organic frameworks for photocatalytic oxidative coupling of amines

As a highly promising candidate for hydrogen storage, crucial to vehicles powered by fuel cells, metal–organic frameworks (MOFs) have attracted the attention of chemists in recent decades. H2 uptak...

Alkaline earth metal ion organic frameworks (AEMOFs) represent a relatively underexplored subcategory of metal-organic frameworks (MOFs). In this contribution, we present the synthesis and structural study of the new MOFs 1-8 based on the alkaline earth ions Mg2+, Ca2+, Sr2+ and Ba2+ and the amino substituted bridging ligands 4-aminonaphthalene-2,6-dicarboxylate (ANDC2-) and 4,8-diaminonaphthalene-2,6-dicarboxylate (DANDC2-). Compounds 1, 5, 6, 7 and 8 constitute rare examples of three-dimensional MOFs which feature square planar M4 secondary building units (SBUs) surrounded by eight bridging ditopic ligands. The underlying topology of MOFs 1, 5, 7 and 8 conforms to the 4-c pcb net which can be simplified to the 8-c bcu net, while 6 adopts the 4-c lta net which simplifies to the 8-c reo net. To the best of our knowledge these are the first examples of MOFs of their structural types formed by linear dicarboxylates instead of trigonal tricarboxylates or tetrahedral tetracarboxylates. Compounds 2, 3 and 4 also feature three dimensional networks with linear rod-shaped SBUs with the Ba2+ MOF 3 displaying an sra rod-net and MOFs 2 and 4 showing very complex rod-nets with so far unique topologies. Fluorescence studies revealed that the free ligands exhibit strong blue-green emission displaying considerable positive solvatochromism thereby pointing towards charge transfer excited states involving the shift of electron density from the amino groups to the aromatic core. Correspondingly, the MOFs display ligand based fluorescence with small differences in emission maxima possibly attributable to the difference in the charge density of the metal ions combined with the different environments around ligands in the crystal structures.

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

In the development of metal-organic frameworks (MOFs), secondary building units (SBUs) have been utilized as molecular modules for the construction of nanoporous materials with robust structures. Under solvothermal synthetic conditions, dynamic changes in the metal coordination environments and ligand coordination modes of SBUs determine the resultant product structures. Alternatively, MOF phases with new topologies can also be achieved by post-synthetic treatment of as-synthesized MOFs via the introduction of acidic or basic moieties that cause the simultaneous cleavage/reformation of coordination bonds in the solid state. In this sense, we studied the solid-state transformation of two ndc-based Zn-MOFs (ndc = 1,4-naphthalene dicarboxylate) with different SBUs but the same pcu topology to another MOF with sev topology. One of the chosen MOFs with pcu nets is [Zn2(ndc)2(bpy)]n (bpy = 4,4′-bipyridine), (6Cbpy-MOF) consisting of a 6-connected pillared-paddlewheel SBU, and the other is IRMOF-7 composed of 6-connected Zn4O(COO)6 SBUs and ndc. Upon post-structural modification, these pcu MOFs were converted into the same MOF with sev topology constructed from the uncommon 7-connected Zn4O(COO)7 SBU (7C-MOF). The appropriate post-synthetic conditions for the transformation of each SBUs were systematically examined. In addition, the effect of the pillar molecules in the pillared-paddlewheel MOFs on the topology conversion was studied in terms of the linker basicity, which determines the inertness during the solid-state phase transformation. This post-synthetic modification approach is expected to expand the available methods for designing and synthesizing MOFs with controlled topologies.

The selective aerobic oxidative coupling of amines under mild conditions is an important laboratory and commercial procedure yet a great challenge. In this work, a porphyrinic metal-organic framework, PCN-222, was employed to catalyze the reaction. Upon visible light irradiation, the semiconductor-like behavior of PCN-222 initiates charge separation, evidently generating oxygen-centered active sites in Zr-oxo clusters indicated by enhanced porphyrin π-cation radical signals. The photogenerated electrons and holes further activate oxygen and amines, respectively, to give the corresponding redox products, both of which have been detected for the first time. The porphyrin motifs generate singlet oxygen based on energy transfer to further promote the reaction. As a result, PCN-222 exhibits excellent photocatalytic activity, selectivity and recyclability, far superior to its organic counterpart, for the reaction under ambient conditions via combined energy and charge transfer.

羟基-乙基)-3氢-苯并咪唑-5-羧酸(Hebimc)和金属锌盐反应得到一种新颖的次级构 筑单元Zn 2 (ebimc) 2 .在此基础上, 通过加入辅助配体和条件优化, 成功合成了4例结构新颖的金属有机框架 (MOFs)材料, 其分子式分别为: Zn 2 (Hebimc) 4 (1), Zn 2 (Hebimc) 2 (BDC)•xG(2, BDC=对苯二甲酸, G=客体分子), Zn 2 (Hebimc) 2 (NDC)•xG(3, NDC=2,6-萘二酸), Zn 8 (ebimc) 6 (DOBDC)(OH) 2 (H 2 O) 2 •xG(4, DOBDC=2,5-二羟基对苯二甲 酸).其中, 化合物1由Zn 2 (Hebimc) 2 单元自身首尾相连形成一维链结构; 在化合物2和3中, 通过加入辅助羧酸配体 BDC或NDC, Zn 2 (Hebimc) 2 单元被辅助配体连接形成二维层状结构; 在化合物4中, 有机碱的加入使得Hebimc配体 上的羧基和咪唑基同时脱去质子, 表现出高的配位能力, Zn

Two comparable Ba‐MOFs with similar linkers for enhanced CO ₂ capture and separation by introducing N‐rich groups

A new metal–organic framework (MOF), [Co(L)2(4,4′-bipy)]n (1) [HL = 4-{[(1-phenyl-1H-tetrazol-5-yl)sulfanyl]methyl}benzoic acid, 4,4′-bipy = 4,4′-bipyridine], has been solvothermally synthesized and characterized by single crystal X-ray diffraction, elemental analysis, infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. As revealed by the single crystal X-ray diffraction, there exist two kinds of the L− ligands that are “Z”-shaped and “U”-shaped L− ligands in complex 1. Two “U”-shaped L− ligands bridge two symmetry-related Co(II) cations to form a dinuclear [Co2(COO)2] secondary building unit (SBU). The adjacent dinuclear SBUs are connected by bipillared 4,4′-bipy ligands to generate an interesting one-dimensional double chain, which is further consolidated by the intrachain π–π interactions between neighbouring pyridyl rings of 4,4′-bipy ligands. These one-dimensional double chains are further linked by multiple interchain C–H···N, C–H···π and π–π weak interactions to form a three-dimensional supramolecular architecture. Thermogravimetric analysis and variable-temperature powder X-ray diffraction studies indicate that complex 1 shows good thermal stability. In addition, the magnetic investigation reveals that complex 1 exhibits an antiferromagnetic interaction between two Co(II) ions in the dinuclear [Co2(COO)2] SBU. A one-dimensional double-chain Co(II) (MOF), [Co(L)2(4,4′-bipy)]n (1) [HL = 4-{[(1-phenyl-1H-tetrazol-5-yl)sulfanyl]methyl}benzoic acid, 4,4′-bipy = 4,4′-bipyridine], has been solvothermally synthesized and characterized. The thermal stability and magnetic property of 1 have been investigated.

Chapter 2 - Secondary building units of MOFs

Synthesis of two new Cd(II)-MOFs based on different secondary building units with highly selective gas sorption for CO2/CH4 and luminescent sensor for Fe3+ and Cr2O72− ions

Metal-organic frameworks (MOFs) are a class of organic–inorganic hybrid materials built from metal-connecting nodes and organic-bridging ligands. They have received much attention in recent years owing to the ability to tune their properties for potential applications in various areas. Properly designed MOFs with uniform, periodically aligned active sites have shown great promise in catalysing shape-, size-, chemo-, regio- and stereo-selective organic transformations. This study reports the synthesis and characterization of two chiral MOFs (CMOFs 1 and 2 ) that are constructed from Mn-salen-derived dicarboxylic acids [salen is ( R , R )- N , N ′-bis(5- tert -butylsalicylidene)-1,2-cyclohexanediamine], bis(4-vinylbenzoic acid)-salen manganese(III) chloride (H 2 L 4 ) or bis(benzoic acid)-salen manganese(III) chloride (H 2 L 3 ) and [Zn 4 (μ 4 -O)(O 2 CR) 6 ] or [Zn 5 (H 2 O) 2 (μ 3 -OH) 2 (O 2 CR) 8 ] secondary building units (SBUs), respectively. The SBUs in CMOF- 1 are connected by the linear ditopic Mn-salen-derived linkers to construct a fourfold interpenetrated isoreticular MOF (IRMOF) structure with pcu topology. In CMOF- 2 , the Mn-salen centres dimerize in a cross-linking way to form a diamondoid structure with threefold interpenetration. CMOF- 1 was examined for highly regio- and stereo-selective tandem alkene epoxidation/epoxide ring-opening reactions by using the Mn-salen andZn 4 (μ 4 -O)(carboxylate) 6 active sites, respectively. Our work demonstrated the potential utility of chiral MOFs with multiple active sites in the efficient synthesis of complex molecules with excellent regio- and stereo-controls

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Solvothermal reactions of Co2+ and Mn2+ salts with 2-(trifluoromethyl)-1H-4,5-imidazole dicarboxylic acid (H3TFMIDC) lead to two novel three-dimensional (3D) metal–organic frameworks (MOFs), namely, [Co6(μ3-TFMIDC)4(H2O)12]·15H2O (1) and [(Me2NH2)3][MnII6 MnIII(μ3-TFMIDC)6(H2O)6]·18H2O (2). Single-crystal X-ray diffraction analysis reveals that both of them are based on interesting planar tetranuclear squares [M4(TFMIDC)4] as secondary building units (SBUs). Compound 1 exhibits a unique 3D two-fold interpenetrated network with the diamondoid topology consisting of the tetranuclear square SBUs as 4-connected nodes, while compound 2 features an unusual (6,16)-connected 3D framework based on the novel tetranuclear square SBUs as 16-connected nodes and trivalent manganese ions as 6-connected nodes, representing the first 16-connected MOF utilizing planar tetranuclear square SBUs as building blocks. Our results open up new perspectives to design novel 3D extended MOFs, especially the unique highly connected 3D MOFs by employing planar tetranuclear square SBUs. Moreover, IR spectroscopy, powder X-ray diffraction, thermogravimetric analyses, and a study on the magnetic properties of both compounds, have been also performed.

A Cu-based metal-organic framework with two types of connecting nodes as catalyst for oxygen activation

This research explores the alteration of metal-organic frameworks (MOFs) using a method called postsynthetic metal exchange. We focus on the shift from a Zn-based MOF containing a [Zn4O(COO)6] secondary building unit (SBU) of octahedral site symmetry (ANT-1(Zn)) to a Fe-based one with a [Fe3IIIO(COO)6]+ SBU of trigonal prismatic site symmetry (ANT-1(Fe)). The symmetry-mismatched SBU transformation cleverly maintains the MOF's overall structure by adjusting the conformation of the flexible 1,3,5-benzenetribenzoate linker to alleviate the framework strain. The process triggers a decrease in the framework volume and pore size alongside a change in the framework's charge. These alterations influence the MOF's ability to adsorb gas and dye. During the transformation, core-shell MOFs (ANT-1(Zn@Fe)) are formed as intermediate products, demonstrating unique gas sorption traits and adjusted dye adsorption preferences due to the structural modifications at the core-shell interface. Heteronuclear clusters, located at the framework interfaces, enhance the heat of CO2 adsorption. Furthermore, they also influence the selectivity of the dye size. This research provides valuable insights into fabricating novel MOFs with unique properties by modifying the SBU of a MOF with flexible organic linkers from one site symmetry to another.