Thiết kết tổng hợp vật liệu khung hữu cơ kim loại mới định hướng ứng dụng làm chất xúc tác quang hoá (tóm tắt)

Constructing by Secondary Building Units SBUs of metal clusters and organic linkerscombination permits the modification of resultant structural modularity fordesigning structure e.g., po

Viet Nam National University – Ho Chi Minh City

Over the past two decades, the prominent growth of Metal OrganicFrameworks (MOFs), a high ordered and porous material class had beenreceiving the pay attention by the research community specially Constructing

by Secondary Building Units (SBUs) of metal clusters and organic linkerscombination permits the modification of resultant structural modularity fordesigning structure (e.g., post-synthetic modification, predesigned linker,defects chemistry) which can be tunable the structural features (e.g., pore size,porosity) to make MOFs address the environment problems as well as thetargeted applications such as gas uptake, separation, catalyst, drug delivery,water treatment

In MOF chemistry, the building block method, whereby discrete,preassembled metal oxo clusters are reacted with well-defined organic linkers,has been utilized to achieve a greater degree of control over MOF construction.However, the isolation and subsequent usage of many discrete metal oxoclusters remains a significant challenge and the relatively slow kineticsoriginating from the association and dissociation of ligands, limits theapplicability of this method Additionally, it is far from given that the desiredMOF structure will be obtained as metal oxo building blocks have beenobserved to rearrange during the synthesis Means of overcoming this lack oftotal synthetic control is to take inspiration from molecular synthesis, in whichcertain conditions have been discovered to achieve specific end products In

this contribution, we articulate a strategy for making discrete metal clusters in situ that are appropriately functionalized to affect imine condensation reactions,

commonly used in the chemistry of covalent organic frameworks (COFs) Wefind that the cluster formation chemistry and that of COFs, when carried out insequence, overcome the challenge of synthetic incompatibility The structural

features of targeted material, termed MOF-901, was fully characterized powderX-ray diffraction and supplemental analyses As a result of the incorporation ofTi(IV) units, MOF-901 was proven to be photocatalytically active and wasapplied to the photocatalyzed polymerization of methyl methacrylate (MMA).

For further investigation the photocatalysis properties of MOF which isisoreticular to MOF-901 structure, MOF-902 was successfully synthesized byenlarging the linking unit, and applied to the application of polymerizationreaction with these kinds of monomer: methylmethacrylate (MMA),benzylmethacrylate (BMA), and styrene (St) Interestingly, based on thecatalysis effect of MOF-902, the molecular weight of polyMMA is as high asthe value of polyMMA which is produced by MOF-901 catalyst, and thepolydispersity index of polyMMA produced by MOF-902 catalyst is lower thanMOF-901 (1.27 compared to 1.60)

Moreover, we have successfully synthesized three novel MOFs termedMOF-903(Fe), MOF-904(Fe), and VNU-18(Cu) based triangular Iron (III)cluster and extraordinary three discrete Cu(II) building units, respectively.These materials were full characterized by the powder X-ray diffraction, singlecrystal X-ray diffraction analysis, thermogravimetric analysis, gas adsorptionstudy MOF-904 and VNU-18 show the permanent porosity with the internalsurface area in calculated of 1200 m2 g-1 and 1000 m2 g-1, respectively, whichare proven by Nitrogen isotherm at 77 K at low pressure

CHAPTER 1 INTRODUCTION TO MOFs 1.1 Introduction

Metal Organic Frameworks (MOFs) are constructed by the rigidcoordination bonds between the organic linkers and inorganic metal ions orclusters as the nodes which is widely designated by Secondary Building Units(SBUs) later The organic linkers are also termed as SBUs in term ofgeometrical views as well It is noted that MOFs have been termed as manynames from the first time of invention (Porous Coordination Polymers (PCPs),Porous Coordination Networks (PCN), hybrid inorganic-organic materials,Metal Organic Materials (MOMs), etc.) Those names presented to the samegeneral type of porous material which links two components of transitionmetals and organic linking units to form the extended structure In fact, an earlyreport in 1979 was published the cyanide-bridged mixed-metal openframework, in which the authors mentioned the similarities between theirnetwork and Zeolites The outbreak of research in crystalline material based onmetal ions and organic bridging ligands was continue in the late 1990’s Thename of “Metal Organic Frameworks” has been become famous and popular byOmar M Yaghi in 1995 More than 20,000 structures of MOFs have beenreported and studied so far showing the tremendous development process ofcrystalline and porous materials MOFs have been considered as the new class

of microporous materials possessing the promising properties of high porosity,well-defined crystallinity, thermal stability, catalytic activity and so on The keypoint of the structural features of MOFs in many cases as gas storage,separation, catalyst, drug delivery is determined by ultrahigh porosity and highinternal surface area of MOFs However, some certain applications: Protonconduction, magnetic behavior, catalyst, are related strictly to the active sites(metal cluster, linker active sites, exchanged counter ions) or post synthesismodification (PSM) to the structure of the host materials instead of high surfacearea of MOFs In general, MOFs can be designed not only by employing the

different metal coordination or diverse linker units but also by embedding aspecific environment to the void space inside the structure The challenging inporous materials (Zeolites, activated carbon, etc.) is controlling the size, shape,functionality of the void space can be achieved in MOFs.

1.2 MOFs composites

MOFs are made from organic linkers and most of metals in periodic table

from rare earth elements to d, f-block transition metals creating the various

chemistry in crystalline porous material The component of metal in MOFs isconsidered as the nodes which can be isolated single point or metal cluster anddirectly linked together by rigid or flexible organic linker units The organicunits (linker or bridging block) which are used to construct MOFs, can becarboxylate commonly or other anions as phosphate, sulfonate, heterocycliccompound rarely As the key function, the targeted applications need to beconsidered firstly by choosing the structure of the linker units Because duringthe MOFs conformation, the organic linkers could effect to the deprotonationprocess as well as the linking interaction with metal ions which cause thegeometrical structure of MOFs In addition, the effect of the structure of thecoordination environment in MOFs includes the geometry of metal atom used

in the synthesis The simple way to express the most influencing to thetopological networks of MOFs is paying attention to the geometry of SBUs.The building blocks of metal cluster are initially formed by the linkagesbetween multi-topic linker such as, 1,4-benzenedicarboxylate (BDC), 1,3,5-benzentricarboxylate (BTC), biphenyl-3,3’,5,5’-tetracarboxylate (BPTA) or1′,2′,3′,4′,5′,6′-hexakis(4-carboxyphenyl)-benzene (CPB) and the metal-oxopieces which are composed in early of reaction process In 1999, Omar M.Yaghi and co-workers published two archetypical MOFs, MOF-5(Zn4O(BDC)3, where BDC = 1,4-benzenedicarboxylate) and MOF-199(Cu3(BTC)2, where BTC = 1,3,5-benzenetricarboxylate) which has beenreckoned as the benchmark in MOFs chemistry by the first showing theultrahigh porosity of porous materials In crystal structure of MOF-5, Zn4O

plays as model SBU presented by many compounds in MOFs chemistry later(Figure 1).

Figure 1 Crystal structure deconstruction for MOF-5 exhibiting clearly 3D

extended framework and topological elucidation

1.3 Interesting features and application of MOFs

MOFs are commonly synthesized by connecting the organic linkers andthe metal salts under solvothermal condition by heating at relatively lowtemperature (lower than 300 C) The crystal structure of final product, MOFs,can be obtained depend on the characteristics of the linkers such as thegeometry, bulkiness, functional groups, rigid or flexible linkages The role ofthe MOFs formation is also indicated by the kinds of metal clusters which areused to react with the organic linkers The mixture of reagents is dissolved inthe single solvent or the co-solvent system to adjust the polarity The importantparameters for the synthesis by using solvothermal method are temperature,reagent concentration, the solubility and pH environment under presence ofadditives or modulators The reticular chemistry is presented by combination ofsimplification of linker units and metal cluster representative (point extension)

to describe the structural characters of MOFs

The high porous material in MOFs chemistry was the first reported in

1999 by Yaghi and co-workers, in which the structure was elucidated by singlecrystal X-ray diffraction, gas sorption at low temperature and low pressuresupported the permanent porosity The forming of the Zn4O(CO2)6 octahedral

building units which made the chelation to carboxylate linker leads to fcu cube

topology The void fraction calculation was found to be 61% with BET surfacearea >2300 m2 g-1 The first time one porous material was totally elucidated thecrystal structure and other characterizations showing the high porositycompared to traditional porous materials such as activated carbon or zeolites(Figure 2)

Figure 2 Statistic for surface area of MOFs comparing to conventional porous

material

Studying of gas storage application has been conducted on poroustraditional material as activated carbon, zeolites, or carbon nanotubes MOFsmaterial recently is being received much attention for gas uptake speciallyhydrogen, carbon dioxide and methane, due to the ultra-high porosity, well-

known structural topology, framework flexibility, tunable pore distribution,leading to the active sites decoration for enhancing the gas affinity.

1.4 Objective

In the chemistry of carboxylate metal−organic frameworks (MOFs), thechelation of the carboxyl organic linker to metal ions gives metal-carboxylclusters, secondary building units (SBUs), which act as anchors ensuring theoverall architectural stability of the MOF Although many of these SBUs areknown as discrete clusters, it has been difficult to directly use them as startingbuilding blocks for MOFs The main reason is the sensitivity of clusterformation to reaction conditions and, in many cases, the incompatibility of suchconditions with those required for MOF synthesis and crystallization Thislimitation has prevented access to the vast, diverse, and well-developed clusterchemistry and the potential richness of properties they would provide to MOFs

Scheme 1 Synthetic scheme depicting the generalized formation of a iscrete

hexameric Titanium Cluster, which can be appropriately functionalized with aminegroups to affect imine Condensation reactions Atom colors: Ti, blue; C, black; O,red; R groups, pink; H atoms and capping isopropoxide units are omitted forclarity

In this contribution, we articulate a strategy for making discrete metalclusters in situ that are appropriately functionalized to affect imine-condensation reactions, commonly used in the chemistry of covalent−organic

frameworks (COFs) We find that the chemistry of cluster formation and COFs,when carried out in sequence, overcome the challenge of syntheticincompatibility Inspired by the chemistry of hexameric titanium oxo clusters,

we reasoned that it is possible to functionalize a known cluster with aminefunctionalized carboxyl ligands (Scheme 1)

Indeed, this allows the resulting cluster to be linked together throughimine condensation reactions Initial synthetic attempts were performed in asequential, stepwise manner, in which a discrete, isolated Ti(IV) cluster,[Ti6O6(OiPr)6(AB)6] (AB = 4-aminobenzoate; OiPr = isopropoxide), was firstsynthesized according to previous reports.116 Based on reticular chemistry, thishexagonal building block has six points-of-extension and when linked with a

linear linker would lead to an hxl layered topology Thus, titanium(IV)

isopropoxide [Ti(OiPr)4] and 4-aminobenzoic acid (H-AB) were reacted undersolvothermal conditions in isopropanol After successful synthesis and fullcharacterization of the cluster, exhaustive efforts were undertaken to form thecorresponding MOF upon reactions with benzene-1,4-dialdehyde (BDA).However, due to the low solubility of the cluster in a variety of solvents, onlypoorly crystalline powders or amorphous solids were obtained Accordingly, aone-pot synthetic approach, with BDA present, was performed given the factthat the synthetic conditions to form the hexameric [Ti6O6(OiPr)6(AB)6] werefound to be robust

CHAPTER 2 SYNTHESIS AND CHARACTERIZATION OF MOF901,

-902, -903, -904, AND VNU-18 2.1 Introduction

The synthesis procedure of MOF-901, -902, -903, -904, and VNU-18 wasdescribed below The solvothermal synthesis method was used to synthesizethese MOFs The crystal structure and physical, chemical properties of theseMOFs were then fully analyzed

2.2 Experiment

MOF-901, -902, -903, -904, and VNU-18 were obtained by solvothermalsynthesis method Specially, MOF-901, and MOF-902 need to be synthesizedunder inert gas and vacuum medium to avoid any effects of water and oxygen.The solvents, which were used in the experiment, are anhydrous

The obtained materials were full characterized to confirm the crystalstructure and the features including power X-ray diffraction (PXRD for MOF-

901, -902), single crystal X-ray diffraction (SXRD for MOF-903, -904, andVNU-18), thermal gravimetric analysis (TGA), Fourier transform infraredspectroscopy (FT-IR), nuclear magnetic resonance (NMR), microelementalanalysis (EA), nitrogen adsorption isotherm at low pressure, 77 K (BET)

2.3 Result and discussion

2.3.1 MOF-901: Synthesis and characterization

- The yield of MOF-901 synthesis is 33.9 % based on titaniumisopropoxide

- Imine linkage in the framework of MOF-901 was proven by Fouriertransform infrared spectroscopy (FT-IR)

- The thermogravimetric analysis (TGA) for activated MOF-901 exhibitsthe thermal stability of MOF-901 up to 200 C

- The amount of TiO2 “residue” after burning under airflow matches withthe theory of model.

- The linker units were confirmed by nuclear magnetic resonance (NMR).The organic linker containing imine linkage was hydrolyzed by HF 48 %

to generate starting reagents: 4-aminobenzoate, and benzenedialdehyde which were proven by 1H-NMR

1,4 The cluster formation is also clarified by nuclear magnetic resonance(NMR) which shows the signal of methoxide caps at 3.15 ppm with theintegration of 3 protons

- The internal surface area of MOF-901 is 550 m2/g based on BET methodwhich strongly agrees with the geometrical area calculated from the (650

MOF-2.3.2 MOF-902: Synthesis and characterization

- The yield of MOF-901 synthesis is 56 % based on titanium isopropoxide

- Imine linkage in the framework of MOF-902 was also proven by Fouriertransform infrared spectroscopy (FT-IR)

- The thermogravimetric analysis (TGA) for activated MOF-901 exhibitsthe thermal stability of MOF-902 up to 200 C

- The amount of TiO2 “residue” after burning under airflow matches withthe theory of model

- The linker units were confirmed by nuclear magnetic resonance (NMR).The organic linker containing imine linkage was hydrolyzed by HF 48 %

to generate starting reagents: 4-aminobenzoate, and biphenyldicarboxaldehyde which were proven by 1H-NMR

4,4’ The cluster formation is also clarified by nuclear magnetic resonance(NMR) which shows the signal of methoxide caps at 3.15 ppm with theintegration of ~3 protons

- The internal surface area of MOF-902 is 400 m2/g based on BET method

- Crystal structure of MOF-902 was simulated by Material Studio v6.0.

software

- Pawley refinement was applied to refine the unit cell parameters of 902

MOF-2.3.3 MOF-903: Synthesis and characterization

- The yield of MOF-903 synthesis is 75 % based on Fe(NO3)3.9H2O

- MOF-903 was obtained by large riced shape single crystal

- Azo linkage in the framework of MOF-903 was proven by Fouriertransform infrared spectroscopy (FT-IR)

- The thermogravimetric analysis (TGA) for activated MOF-903 exhibitsthe thermal stability of MOF-903 up to 250 C

- The amount of Fe3O4 “residue” after burning under airflow matches withthe theory of model

- Crystal structure of MOF-903 was determined by single crystal X-raydiffraction (SXRD)

- Simulated PXRD pattern for MOF-903 is coincident with theexperimental PXRD pattern

2.3.4 MOF-904: Synthesis and characterization

- The yield of MOF-903 synthesis is 75 % based on Fe(NO3)3.9H2O

- MOF-903 was obtained by octahedral shape single crystal.

- The thermogravimetric analysis (TGA) for activated MOF-903 exhibitsthe thermal stability of MOF-904 up to 270 C

- The amount of Fe3O4 “residue” after burning under airflow matches withthe theory of model

- The internal surface area of MOF-904 is 1200 m2/g based on BET methodwhich strongly agrees with the geometrical area calculated from the (1500

2.3.5 VNU-18: Synthesis and characterization

- The yield of VNU-18 synthesis is 75 % based on Cu(NO3)2.3H2O

- VNU-18 was obtained by light blue single crystal with the needle shape

- The thermogravimetric analysis (TGA) for activated VNU-18 exhibits thethermal stability of VNU-18 up to 200 C

- The amount of CuO “residue” after burning under airflow matches withthe theory of model

- The surface area of VNU-18 was determined by nitrogen adsorptionisotherm at low pressure, and 77 K, which shows the value of 1000 m2/g.That value is coincident with the geometry surface area generated fromthe model structure

- Crystal structure of VNU-18 was determined by single crystal X-raydiffraction (SXRD)

- Topology of VNU-18 was analyzed by TOPOS 4.0 package