Synthesis of cobalt and iron based metal organic frameworks and their applications

Among of these, VNU-15 VNU=Vietnam National University was investigated for proton conductivity with the accounted value, which is higher than nafion, at more practical working condition

CONTENTS

INTRODUCTION 1

CHAPTER 1: THE CHEMISTRY & APPLICATIONS OF METAL ORGANIC FRAMEWORKS 3

1.1 Definition of Metal Organic Framework 3

1.2 Applications of Metal-organic Frameworks 4

1.2.1 Applications of Metal organic Frameworks as Heterogeneous Catalysis 4

1.2.1.1 Metal-organic Frameworks as Scaffold for Oxidative Transformation of Organic Substrates 5

1.2.1.1.1 Cobalt-based MOFs for Oxidative Transformation of Small Organic Substrates 5

1.2.1.1.2 Metal-organic Frameworks for Oxidative Conversation of Large Organic Substrates 7

1.2.1.2 Strategy for Design the Catalytic Active Centers in MOFs 9

1.2.1.2.1 Metal Clusters as the Catalytic Active Sites in MOFs 9

1.2.1.2.2 Functional Linkers as Catalytic Active Sites in MOFs 10

1.2.1.2.3 Post-Modification Strategy for Incorporating Catalytic Active Sites into MOFs 12

1.2.1.2.4 Immobilization of Catalytic Active Guests into MOFs via Self-Assembly 13 1.2.2 MOFs for Proton Conduction 15

1.2.2.1 Water-mediated Proton Conducting MOFs 16

1.2.2.1.1 Design Strategy toward High Proton Conductivity MOFs under Humidity Condition 16

1.2.2.1.1.1 Doping Proton Donors Molecules into the MOFs 16

1.2.2.1.1.2 Coordinately Unsaturated Metal Sites Approach 17

1.2.2.1.1.3 Acidic Functional Groups Approach 17

1.2.2.1.1.4 Defect Sites Approach 18

1.2.2.1.1.5 Water-mediated Proton Conductivity of MOFs 18

1.2.2.2 Anhydrous proton-conducting MOFs 20

CHAPTER 2: SYNTHESIS OF THE NOVEL METAL-ORGANIC FRAMEWORKS AND MATERIAL CHARACTERIZATIONS 22

2.1 Introduction 22

2.1.1 The Modular Nature in Design and Synthesis of MOFs and The Quest to Design and Synthesize New MOFs 22

2.1.2 Objective 24

2.1.3 Approach 24

2.2 Materials and Instrumentation 24

2.2.1 Materials 24

2.2.2 Single Crystal X-ray Diffraction (SC-XRD) and Powder X-ray Diffraction (PXRD) Data Collection 25

2.2.3 Instruments for Characterization of VNU-10, VNU-15, Fe-NH2BDC, Fe-BTC 26 2.3 Material Synthesis, Single Crystal Structure Analysis and Characterization for VNU-10 27

2.3.1 Synthesis of VNU-10 27

2.3.2 Crystal Structure of VNU-10 27

2.3.3 Characterization of VNU-10 31

2.3.3.1 Microscope Image of VNU-10 31

2.3.3.2 PXRD Analysis of VNU-10 31

2.3.3.3 FT-IR Analysis of activated VNU-10 32

2.3.3.4 Thermogravimetric Analysis of VNU-10 33

2.3.3.5 Gas Adsorption Measurements 33

2.4 Material Synthesis, Single Crystal Structure Analysis and Characterization for the Novel structure of VNU-15 35

2.4.1 Synthesis of VNU-15 35

2.4.2 Crystal Structures of VNU-15 36

2.4.3 Characterization of VNU-15 40

2.4.3.1 Microscope Image of VNU-15 40

2.4.3.2 PXRD Analysis for VNU-15 40

2.4.3.3 FT-IR Analysis of activated VNU-15 41

2.4.3.4 Thermogravimetric Analysis of VNU-15 42

2.4.3.5 Porosity and Gas Adsorption of VNU-15 43

2.4.3.6 Water Uptake, PXRD and FT-IR of Corresponding VNU-15 Sample 45

2.5 Material Synthesis, Single Crystal Structure Analysis and Characterization for the Novel structure of Fe-NH2BDC 46

2.5.1 Synthesis of Fe-NH2BDC 46

2.5.2 Crystal Structures of Fe-NH2BDC 47

2.5.3 Characterization of Fe-NH2BDC 50

2.5.3.1 Microscope Image of Fe-NH2BDC 50

2.5.3.2 PXRD Analysis of Fe-NH2BDC 50

2.5.3.3 FT-IR Analysis of activated Fe-NH2BDC 51

2.5.3.4 Thermogravimetric Analysis of Fe-NH2BDC 51

2.6 Material Synthesis, Single Crystal Structure Analysis and Characterization for the Novel structure of Fe-BTC 52

2.6.1 Synthesis of Fe-BTC 52

2.6.2 Crystal Structures of Fe-BTC 53

2.6.3 Characterization of Fe-BTC 55

2.6.3.1 PXRD Analysis of Fe-BTC 55

2.6.3.2 Thermogravimetric Analysis of Fe-BTC 56

CHAPTER 3: APPLICATIONS OF VNU-10 AND VNU-15 57

3.1 NEW TOPOLOGICAL Co2(BDC)2(DABCO) AS HIGHLY ACTIVE HETEROGENEOUS CATALYST FOR AMINATION OF OXAZOLES VIA OXIDATIVE C-H/N-H COUPLINGS 57

3.1.1 The Quest for Large Pore Window (above 15 Å) and High Surface Area (above 2600 m2 g-1) MOFs as Catalyst for Large Substrate Conversions 57

3.1.2 Direct Amination of Azoles under Mild Reaction Conditions 58

3.1.3 Objective 59

3.1.4 Approach 59

3.1.5 Method for Catalysis Study 60

3.1.5.1 Method for Gas Chromatographic 60

3.1.5.2 GC Calculation and analysis 61

3.1.5.3 Method for Catalytic studies 61

3.1.5.4 Synthesis of Reported MOFs 62

3.1.6 Investigations on VNU-10 Catalytic Performance for Direct Oxidative Amination of Benzoxazole with Piperidine 62

3.1.6.1 Conditions Screening for Direct Oxidative Amination of Benzoxazole with Piperidine Using Heterogeneous VNU-10 62

3.1.6.1.1 Effect of Reagent Ratio on GC Yield 63

3.1.6.1.2 Effect of Catalyst Loading on GC Yield 64

3.1.6.1.3 Effect of Various Solvents on GC Yield 65

3.1.6.1.4 Effect of Various Acids on GC Yield 66

3.1.6.1.5 Effect of Various Oxidants on GC Yield 68

3.1.6.1.6 Optimizing Condition for Amination of Benzoxazole Reaction Using VNU-10 Catalyst & Product Analysis by 1H-NMR and 13C-NMR 70

3.1.6.2 Advantages of VNU-10 for Amination of Benzoxazole Reaction over Other Heterogeneous and Homogeneous Catalyst 71

3.1.6.3 The Heterogeneous Nature of VNU-10 74

3.1.6.4 Greener Protocol to Benzoxazole Amine Compounds by Recycling of VNU-10 76

3.1.6.5 Synthesis of Diverse Benzoxazole Amine Derivatives with Different Amine Substitutes 78

3.2 HIGH PROTON CONDUCTIVITY AT LOW RELATIVE HUMIDITY IN AN ANIONIC Fe-BASED METAL-ORGANIC FRAMEWORK 80

3.2.1 Introduction of Hydrogen Fuel Cell, Impedance and Nyquist Plot of Impedance 80

3.3.1.1 Hydrogen Fuel Cell 80

3.3.1.2 Definition of Impedance and Nyquist Plot of Impedance 82

3.2.2 The Quest of Proton Conducting Membrane that Maintain High Conductivity at High Temperature and Low Humidity 83

3.2.3 Objectives 84

3.2.4 Approach 84

3.2.5 Method for Proton Conductivity Measurement 84

3.2.5.1 Preparation of Pelletized VNU-15 and Proton Conductivity Measurement 84

3.2.5.2 Data Proceeding to Obtain Proton Conductivity 85

3.2.6 Investigation for the Proton Conductivity of VNU-15 86

3.2.6.1 Correlation between Structure of VNU-15 and Proton Conductivity 86

3.2.6.2 Proton Conductivity Measurement of VNU-15 under Low Humidity at 95 °C 87

3.2.6.3 Exploration of the Proton Conduction Mechanism of pelletized VNU-15 89

3.2.6.4 Investigation for the Stability of VNU-15 during Proton Conductivity Measurement 92

3.2.6.5 Investigation for the Working Stability of VNU-15 as Function of Time & Conductivities under 55 and 60% RH at 95 °C 95

CONCLUSION 97

List of Publications 99

References 100

List of Figures

Fig 1 Structure of MOF-5 constructed from Zn4O(CO2)6 cluster and BDC2- linker 3

Fig 2 Recent progress on synthesizing high surface area material 3 Fig 3 a) Crystal structure of PCN-222; b) Peroxidase-like oxidation reaction of

pyrogallol catalyzed by PCN-222(Fe) 7

Fig 4 a) Crystal structure of PCN-600(Fe); b) Enzyme mimetic co-oxidation of phenol

and 4-aminoantipyrine catalyzed by PCN-600(Fe) 8

Fig 5 a) [Co4Cl]7+ secondary building unit and the crystal structure of Co-btt; b) Epoxides ring opening reaction carried out by Co-btt catalysis 9

Fig 6 a) Crystal structure of ZIF-9; b) The CO2 reduction reactions catalysis by ZIF-9 10

Fig 7 a) Structure of ZnPO-MOF and corresponding linker to construct the MOF; b)

Mechanism for acyl-transfer reaction catalyze by ZnPO-MOF 11

Fig 8 a) Urea MOF strategy; b) Catalytic activities of NU-601 12 Fig 9 a) Post-modified MIL-101 by sequent combination between Brønsted acid and

Lewis acid sites; b) Investigated the benzylation reaction of mesitylene with benzyl alcohol; c) Compared catalytic activity of MIL-101-Cr-SO3H·Al(III) with other catalysts 12

Fig 10 One-Pot Synthesis of the MIL101-Anchored Nickel Complex,

Fig 13 Structure of VNU-10, the paddle wheel cluster are connected with BDC2- by

two different way to form the DABCO connected kgm layers of VNU-10 and DABCO connected sql layer of Co2(BDC)2(DABCO) C, black; O, red; Co, light blue; N, blue;

H was omitted for clarity 28

Fig 14 Crystal structure of VNU-10 represented in DABCO connected kgm layers; a) Vertexes and edges assignment for cobalt nodes and linkages of VNU-10; b) Structure of VNU-10 represented in DABCO connected kgm layers Black, BDC2-; Blue, DABCO; light blue, paddle wheel cobalt nodes; yellow, linkages between iron nodes 28

Fig 15 Thermal ellipsoid plot of the asymmetric unit of VNU-10 with 30% probability C, black; O, red; Co, light blue; N, blue; H, white 29

Fig 16 Green needle crystal of VNU-10 at forty zooming times 31

Fig 17 The calculated PXRD pattern of VNU-10 from single crystal data (red) compared with the experimental patterns from the as-synthesized VNU-10 (orange) and Co2(BDC)2DABCOsql (Black) 32

Fig 18 FT-IR of activated VNU-10; inset: zooming with wavelength from 1450 to 1690 cm-1 32

Fig 19 Thermogravimetric analysis of VNU-10 in air stream under 20% O2 and 80% N2 33

Fig 20 N2 adsorption isotherm of VNU-10 at 77 K 34

Fig 21 CO2, CH4, N2 adsorption isotherm of VNU-10 at 273 K 34

Fig 22 CO2, CH4, N2 adsorption isotherm of VNU-10 at 298 K 35

Fig 23 Crystal structure of VNU-15 is constructed from BDC2- and NDC2- linkers that stitch together corrugated infinite rods of [Fe2(CO2)3(SO4)2(DMA)2]∞ (a) These

corrugated infinite rods propagate along the a and b axes to form the three-dimensional

architecture The structure is shown from the [110] and [001] plans (b, c, respectively)

Atom colors: Fe, orange and blue polyhedra; C, black; O, red; S, yellow; N, blue; and DMA cations, light blue All other H atoms are omitted for clarity 37

Fig 24 Representation of the fob topology that VNU-15 adopts a) Vertexes and edges

assignment for iron nodes and linkages of VNU-15; b) Structure of VNU-15

represented in fob topology Atom colors: Fe, orange and blue polyhedra; C, black; O,

red; S, yellow; N, blue; and DMA cations, light blue All other H atoms are omitted for clarity 38

Fig 25 Thermal ellipsoid plot of the asymmetric unit of VNU-15 with 50% probability

C, black; O, red; Fe, orange; S, yellow; N, blue; H, white 40

Fig 26 Orange octahedral crystal of VNU-15 at forty zooming times 40 Fig 27 The calculated PXRD pattern of VNU-15 from single crystal data (black)

compared with the experimental patterns from the as-synthesized sample (blue) and samples after activation at 100 °C (red) 41

Fig 28 FT-IR spectra of activated VNU-15 42 Fig 29 Thermogravimetric analysis of VNU-15 in air stream with 20% O2 and 80%

N2 42

Fig 30 CO2, CH4, N2 adsorption isotherm of VNU-15 at 298 K 43

Fig 31 CO2, CH4, N2 adsorption isotherm of VNU-15 at 273 K 44

Fig 32 Water uptake of VNU-15 at 25 °C as a function of P/P0 ranging from 8% to

80% Inset: Water uptake of VNU-15 at 25 °C with P/P0 ranging from 8% to 62.58% 45

Fig 33 PXRD analysis of VNU-15 exhibiting the long range order of the structure was

retained after water uptake up to 60% RH at 25 °C The experimental pattern (red) corresponded well with the simulated (black) diffraction pattern of VNU-15 from single crystal data 45

Fig 34 FT-IR spectra of VNU-15, post H2O uptake at 60% RH, as compared with activated VNU-15 46

Fig 35 Structure of Fe-NH2BDC: a) Fe2(CO2)4(SO4)2 clusters were connected by NH2BDC to form Fe-NH2BDC; b) Connected sql layers through hydrogen bond between

-(CH3)2NH2+ and sulphate ligand; c) Crystal structure of Fe-NH2BDC represents in sql

layers Atom color: C, black; O, red; Fe, orange polyhedra; S, yellow; N, blue; H of nitrogen, white; H atoms connected to carbon are omitted for clarity 47

Fig 36 Thermal ellipsoid plot of the asymmetric unit of Fe-NH2BDC with 30% probability C, black; O, red; Fe, orange; S, yellow; N, blue; H, white; Cu green 48

Fig 37 Orange blocked crystal of Fe-NH2BDC at eighty zooming times 50

Fig 38 The calculated PXRD pattern of Fe-NH2BDC from single crystal data (black) compared with the experimental patterns from the as-synthesized sample (red) 50

Fig 39 FT-IR of activated Fe-NH2BDC 51

Fig 40 Thermogravimetric analysis of activated Fe-NH2BDC in air stream with 20%

O2 and 80% N2 52

Fig 41 Crystal structure of Fe-BTC is constructed from BTC3- linkers and two different SBU: tetrahedral single iron atom SBU and the iron paddle wheel SBU (a); The crystal

structure of Fe-BTC viewed along [001] plan (b); The mmm-a topology of Fe-BTC

(c) Atom colors: Fe, blue polyhedra; C, black All other H atoms are omitted for clarity Atom colors: Fe, blue polyhedra; C, black; O, red; S, yellow; N, blue; and DMA cations, light green All other H atoms are omitted for clarity 53

Fig 42 Thermal ellipsoid plot of the asymmetric unit of Fe-BTC with 30% probability

C, black; O, red; Fe, orange; S, yellow; N, blue; H, white 55

Fig 43 The calculated PXRD pattern of Fe-BTC from single crystal data (black)

compared with experimental patterns from the as-synthesized sample (red) 55

Fig 44 Thermogravimetric analysis of activated Fe-BTC in air stream with 20% O2 and 80% N2 56

Fig 45 Effect of benzoxazole/piperidine molar ratio on GC yield of

Fig 53 13C-NMR spectrum of 2-(piperidin-1-yl)benzoxazole products 71

Fig 54 Different MOFs as catalyst for the direct benzoxazole amination reaction 72 Fig 55 Difference in activity between VNU-10 and cobalt salts as catalyst for the direct

benzoxazole amination reaction 73

Fig 56 Compare activity of VNU-10 with smaller pore MOFs, zeolite, oxide & cobalt

salts as catalyst for the direct benzoxazole amination reaction 74

Fig 57 Leaching test with catalyst removal during reaction course Conversion

percentage as a function of reaction time in the presence of the VNU-10 catalyst (filled circle) and once VNU-10 was removed 5 min after the reaction started (open circle) 75

Fig 58 Investigate the recycling ability of VNU-10 catalyst 77 Fig 59 Coincided PXRD of the fresh and reused VNU-10 77

Fig 60 Coincided FT-IR of the fresh and reused VNU-10 78 Fig 61 Conversion of benzoxazole to diverse benzoxazole amine derivatives under

optimized conditions using different amines moieties 79

Fig 62 Typical structure of Hydrogen fuel cell 80 Fig 63 Typical Nyquist plot and an equivalent circuit used for fitting Schematic

representations: R c /R m , resistor; W, Warburg diffusion element; C, capacitor 82

Fig 64 An equivalent circuit used for fitting Schematic representations: R1/R2/R3,

resistor; W1, Warburg diffusion element; Q1/Q2/Q3, imperfect capacitor 85

Fig 65 Nyquist plot derived from equivalent circuit (black line) and experimental

Nyquist plot (blue circles) of pelletized VNU-15 under 60% RH at 25 °C Frequency ranged from 1 MHz to 10 Hz Inset: Zoom of Nyquist plot at high frequency 85

Fig 66 Nyquist plot derived from equivalent circuit (black line) and experimental

Nyquist plot (blue circles) of pelletized VNU-15 under 60% RH at 95 °C Frequency ranged from 1 MHz to 10 Hz Inset: Zoom of Nyquist plot at high frequency 86

Fig 67 Nyquist plots of pelletized VNU-15 under 30% RH at 95 °C (red circles) Inset:

Nyquist plots of pelletized VNU-15 under 40% RH (brown circles), 50% RH (green circles) and 55% RH (blue circles) at 95 °C 87

Fig 68 Dependence of proton conductivity in VNU-15 as a function of relative

humidity at 95 °C Inset: Nyquist plot of VNU-15 at 60% RH 88

Fig 69 Nyquist plots resulting from ac impedance analysis of VNU-15 under 55% RH

when heating and cooling from 25 ºC to 95 ºC 90

Fig 70 Nyquist plots resulting from ac impedance analysis of VNU-15 under 60% RH

when heating and cooling from 25 ºC to 95 ºC 91

Fig 71 Arrhenius plot of VNU-15 under 55 and 60% RH at elevated temperature 92 Fig 72 Simulated PXRD pattern of VNU-15 (black) as compared to the experimental

50% RH for 16 hours at each RH followed by ac impedance analysis at temperatures ranging from 25 to 95 ºC (blue) 93

Fig 73 FT-IR of activated VNU-15 (black) as compared to the experimental spectrum

after subjecting pelleted VNU-15 to 30, 40, and 50% RH for 16 hours at each RH followed by ac impedance analysis at temperatures ranging from 25 to 95 ºC (red) 93

Fig 74 Simulated PXRD pattern of VNU-15 (black) as compared to the experimental

patterns from pelleted VNU-15 (red) and subjected to 60% RH for 16 hours followed

by ac impedance analysis (green) 94

Fig 75 FT-IR of activated VNU-15 (black) as compared to the experimental spectra

of pelletized VNU-15 that was subjected to 60% RH for 16 hours followed by ac impedance analysis at 25 ºC (red) and 95 ºC (blue) 94

Fig 76 Nyquist plot of VNU-15 at 55 (blue circles) and 60% RH (red circles) at 95 ºC

after 40 h of consecutive ac impedance measurements 95

Fig 77 Time-dependent proton conductivity of VNU-15 at 55% RH (blue circles)

and 60% RH (red circles) and 95 ºC 95

List of Tables

Table 1 Published MOFs for water-mediated proton conduction and its

conductivity 18

Table 2 Published MOFs for anhydrous proton conduction and its conductivity 21

Table 3 Famous MOFs that was synthesized by commercial linkers 23

Table 4 Crystal data and structure refinement for VNU-10 30

Table 5 CO2, CH4, N2 uptake at 802 Torr and selectivity in adsorption of CO2 over CH4 and N2 of VNU-10 35

Table 6 Crystal data and structure refinement for VNU-15 39

Table 7 CO2, CH4, N2 uptake at 802 Torr and selectivity in adsorption of CO2 over CH4 and N2 44

Table 8 Crystal data and structure refinement for Fe-NH2BDC 49

Table 9 Crystal data and structure refinement for Fe-BTC 54

Table 10 Catalyst and window aperture 72

Table 11 Relative humidity & proton conductivity dependence of VNU-15 at 95 ºC. 88

Table 12 Proton conductivity of VNU-15 in comparison with other water-mediated ultrahigh proton conducting MOFs 89

Table 13 Temperature & proton conductivity dependence of VNU-15 at 55 and 60% RH 91

List of Schemes

Scheme 1 Formation of the observed products through the reaction of tert-butyl peroxy

radicals with cyclohexene (b) Mechanism for the formation of tert-butylperoxy radicals catalysed by the cobalt(II) centres in [CoII

4O(bdpb)3] Their further reaction with cyclohexene, forming the main product.16,17 6

Scheme 2 Synthetic scheme for crystallizing green, needle VNU-10 27 Scheme 3 Synthetic scheme for crystallizing reddish-yellow, octahedral VNU-15 36 Scheme 4 Synthetic scheme for reddish-yellow, blocked shape crystal of Fe-NH2BDC 47

Scheme 5 Synthetic scheme for reddish-yellow, blocked shape crystal of Fe-BTC 52 Scheme 6 Plausible mechanism of direct amination of azoles.123 59

Scheme 7 Amination of Benzoxazole through N-H/CH bonds activation using

Scheme 14 General experimental procedure to 2-(piperidin-1-yl)benzoxazole 70

Abbreviation

PEMFCs Proton Exchange Membrane Fuel Cells

NH2-H2BDC Aminoterephthalic Acid

H2NDC 1,6-naphthalene dicarboxylic Acid

H2BDC 1,4-benzene dicarboxylic Acid

FT-IR Fourier Transform Infrared Spectroscopy

AAS Atomic Absorption Spectroscopy

1H-NMR Proton Nuclear Magnetic Resonance

13C-NMR Carbon-13 Nuclear Magnetic Resonance

INTRODUCTION

Recently, more than 20.000 different metal-organic frameworks (MOFs) have been reported.1 Several of these were found to have the capabilities to solve modern challenges Despite the significant progress in synthesis and applications of MOFs, there are maintained challenges sought to overcome by novel MOFs, which possess novel or enhanced properties For examples:

i The global demand of cleaner and sustainable energy required the development of better hydrogen fuel cells (HFCs), which could turn hydrogen into electric power and release water However, the low concentration of CO impurity in H2 fuel stream, which can poison at the Pt catalyst of HFCs, hence the effectively working condition was identified at medium temperature (T ≥ 100 °C) under low relative humidity (RH), at which, higher CO tolerance of Pt catalyst was accounted for as well as reducing the associating cost to maintain high RH at T ≥ 100 °C Unfortunately, the current technology, which utilized nafion proton conducting membrane (the key components within HFCs) could not well support for above working condition, hence, the quest to synthesize PEMFCs which can satisfactorily function at medium temperature (T ≥ 100 °C) under low RH was raised as top urgent goal.2 Recently, MOFs were investigated as proton conducting membrane in hydrogen fuel cells (PEMFCs), which could achieve the equal conductivity of nafion although high relative humidity were required, thus, developing MOFs which can efficiently function at practical working condition of PEMFCs maintained as significant challenges quested to overcome.3

ii The demand for highly porous material with uniform and large pore aperture, which can serve as host scaffold for the catalytic transformation of large organic substrates, which could not be proceeded by porous material with smaller pore aperture as well as avoiding the utilization of homogenous catalyst which consequently contaminated the product Due to the modular nature of MOFs, its

pore size can be easily to expanse by employing right combination of metal clusters and organic linkers, thus opening the approaches to the solution for accounted challenges

In our scope of exploration, we employed the cheap and commercial linkers as well

as earth abundant metals such as iron and cobalt to synthesize the novel metal-organic frameworks Subsequently, the newly discovered crystal structure were employed as standpoint for initially justifying the interesting properties of novel MOFs to use in relevant applications

In detail, four new metal-organic frameworks have been synthesized and basing on material architecture, we could able to employ for relevant applications Among of these, VNU-15 (VNU=Vietnam National University) was investigated for proton conductivity with the accounted value, which is higher than nafion, at more practical working condition of HFCs (low RH and medium temperature).4 Furthermore, the material, named VNU-10, with large and uniform pore size demonstrated high catalytic activity over other MOFs, ZIFs with smaller pore size in catalytic transformation of large organic substrates.5 Applications for other new materials, namely, Fe-NH2-BDC and Fe-BTC, are still under investigations

CHAPTER 1: THE CHEMISTRY & APPLICATIONS OF ORGANIC FRAMEWORKS

METAL-1.1 Definition of Metal Organic Frameworks

Metal organic frameworks (MOFs) is the compound which are consisted of metal clusters and linker, typically, polytopic organic carboxylates was employed, for example 1,4-benzenedicarboxylic acid (H2BDC), to construct two-, or three-dimensional structures which can be porous (Figure 1).6

Fig 1 Structure of MOF-5 constructed from Zn4O(CO2)6 cluster and BDC2- linker.6

Fig 2 Recent progress on synthesizing high surface area material.1

Recently, more than 20.000 different MOFs have been reported.1 Among these materials, the highest surface area is 7140 m2 g-1, which far exceeding those of traditional porous materials such as zeolites and activated carbons (Figure 2).7,8

1.2 Applications of Metal-organic Frameworks

Due to high porosity and the modular nature of MOF design and synthesis, in which the backbone components [e.g inorganic and organic secondary building units (SBUs)], can be easily tailored, MOFs is promised for diverse applications such

as gas storage and separation,9 catalysts,10 proton conduction,3 sensor,11 light harvest,12drug delivery,13 batteries and supercapacitors,14 and so on.1,15

1.2.1 Applications of Metal-organic Frameworks as Heterogeneous Catalysis

Catalysts, generally, were classified into homogenous and heterogeneous, in which, the homogenous catalysts were recognized for fast kinetic and high conversion in organic synthesis, albeit, several drawbacks have been accounted for, which including the difficulties to separate the catalysts for recycling investigations as well as desired products were usually contaminated by catalyst or decomposed products of catalyst On the other hand, heterogeneous catalyst was recognized as greener pathway for organic synthesis owning to its convenience for recycling, in which, the catalysts can be easily separated from the reaction mixture Despite significant advantage of heterogeneous catalysts, organic synthesis employed these catalysts, mostly resulted in low conversion, hence, one of interesting research direction in the catalytic field has been devoted to develop more efficiently heterogeneous catalysts

Traditional heterogeneous catalysts include metal oxides, polymer resin, silica gel and zeolites, for which, low surface area of metal oxides, polymer resin as well as the small pore aperture of zeolite, preventing the large organic substrates from reaching catalytic centers, thus limiting the use for the transformation of large organic substrates Another platform, mesoporous silica gel, which possessed large pore and high surface

area, however, the structure and pore size of the materials are not uniform and the immobilization of active centers within its pore has maintained challenges

Oxidative transformation of large organic substrates, commonly required the formation of active radicals or high oxidation state of the metal centers, which is unstable with very short decay time, hence required fast diffusion of organic substrate onto the catalytic active sites Recently, MOFs have been employed as the platform for catalytic synthesis of diverse organic compounds.10 In fact, most of published MOFs possessed the small pore aperture with low surface area (less than 8 Å and 2000 m2 g-

1), some of most noticeable MOFs have large internal surface areas and ultralow densities.7 Due to the large and uniform pore size and definitely coordinative environment of metal active centers, a few MOFs catalysts exhibited interesting properties for oxidative transformation of large organic substrates, however, the examples for these class of catalytic reactions are still very rare

1.2.1.1 Metal-organic Frameworks as Scaffold for Oxidative Transformation of Organic Substrates

1.2.1.1.1 Cobalt-based Metal-organic Frameworks for Oxidative Transformation of Small Organic Substrates

The pyrazolate-based materials, namely, [CoII4O(bdpb)3]n were prepared by Volkmer in the reactions of H2bdpb and CoCl2·6H2O The structure of [CoII

4O(bdpb)3]n

was deduced to adopt pcu net which is similar to MOF-5 with encloses octahedral

{Co4O(dmpz)6} nodes instead of {Zn4O(CO2)6} The pore size of the material was found to be 18.1 Å [CoII

4O(bdpb)3]n has permanent porosity, which was confirmed by

an argon gas sorption experiment The BET surface areas of [CoII4O(bdpb)3]n were calculated from the adsorption data to give of 1525 m2 g-1 Similar reaction scheme of

H2bdpb with Co(NO3)2·6H2O leading to the formation of [CoII(bdpb)]n which constructed from the cobalt rod SBU and bdpb2- in order to form three dimension square grid framework [CoII(bdpb)]n possessed 1D channel with the diagonal length of 18.6

Å.16

Scheme 1 Formation of the observed products through the reaction of tert-butyl peroxy

radicals with cyclohexene (b) Mechanism for the formation of tert-butylperoxy radicals catalysed by the cobalt(II) centres in [CoII

4O(bdpb)3] Their further reaction with cyclohexene, forming the main product.16,17

Liquid-phase oxidation of cyclohexene using TBHP as the oxidant of [CoII

4O(bdpb)3]n and [CoII(bdpb)]n catalysts were investigated The maximum cyclohexene conversion after 22 h for [CoII

4O(bdpb)3] is 27.5% and 16% for [CoII(bdpb)] The main reaction products obtained using both catalysts were tert-butyl-2-cyclohexenyl-1-peroxide, followed by 2-cyclohexen-1-one and cyclohexene oxide (Scheme 1).17

Recently, significant advances have been observed in the cyclohexene oxidation reaction using cobalt-based MOFs For example, a novel cobalt-based MOF, formulated as Co3(OH)2-(tpta)(H2O)4 (tpta = terphenyl-3, 2’’, 5’’, 3’-tetracarboxyate) has been synthesized Material characterization revealed that the material could be dehydrated by heating to transform into dehydrated Co3(OH)2(tpta) Heterogeneous catalytic experiments on allylic oxidation of cyclohexene show that Co3(OH)2(tpta) has

6 times enhanced catalytic activity than Co3(OH)2-(tpta)(H2O)4, hence coordinatively unsaturated CoII sites in Co3(OH)2(tpta) have played a significant role in oxidation of cyclohexene The maximum conversion for the system was observed around 73.6%.18Subsequently, similar oxidative transformation of cyclohexene was carried on Ni-

MOF-74, Co-MOF-74 and the mixed of Co & Ni-MOF-74 by Zhaohui Li et all The results revealed that introduction of active Co into the Ni-MOF-74 framework enabled the inert Ni-MOF-74 to show activity for cyclohexene oxidation with the maximum conversion of 54.7% Furthermore, the superior catalytic performance, compared with pure Co-MOF-74, was observed.19

1.2.1.1.2 Metal-organic Frameworks for Oxidative Conversation of Large Organic Substrates

Although the oxidative transformation of small organic substrates could be proceeded by MOFs, it is rare examples for which the oxidative transformation large organic substrates, except for the couple cases, in which, the MOFs catalyst possessed large pore size with porphyrin active centers

Fig 3 a) Crystal structure of PCN-222; b) Peroxidase-like oxidation reaction of pyrogallol

catalyzed by PCN-222(Fe).20

Recently, Zhou et al published a porphyrin-based MOF, named PCN-222 and took advantage of large pore size of material with porphyrin active center to use for catalyst The self-assembly of tetrakis(4-carboxyphenyl)porphyrin) and zirconium cluster

leaded to csq framework, in which, the architecture contained hexagonal and triangular

one dimension channels with diameter of 36 and 8 Å (Figure 3a) The iron analogue

PCN-222(Fe) employed to test the catalytic activity for the oxidative conversation of several substrates, included pyrogallol, 3,3,5,5-tetramethylbenzidine, and o-

phenylenediamine Taken in note, very high kinetic parameters (kcat, 16.1 min-1) for oxidative conversation of pyrogallol by PCN-222(Fe) which was several times faster free homogeneous hemin catalyst (Figure 3b).20

Fig 4 a) Crystal structure of PCN-600(Fe); b) Enzyme mimetic co-oxidation of phenol and

4-aminoantipyrine catalyzed by PCN-600(Fe).21

Later on, Zhou group published the iron-based MOF, named PCN-600(Fe), which

adopted stp-a topology and possessed a giant pore size (3.1 nm) (Figure 4a)

Subsequently, the iron analogue, PCN-600(Fe), was employed for enzyme mimetic oxidation of phenol and 4-aminoantipyrine (Figure 4b) Albeit lower reaction speed of

co-the catalyst was observed in comparing with cytochrome (kcat: 0.66 min-1 for 600(Fe) and 9.59 min-1 for cytochrome), the authors could claim for the higher efficiency of PCN-600(Fe) active centers despite the low speed, which caused by low diffusion of substrates.21

PCN-1.2.1.2 Strategy for Design the Catalytic Active Centers in MOFs

Typically, metal clusters played the catalytic active sites in MOFs,22–27 on the other hand, the active sites were also anchored into MOFs framework via the linkers before the self-assembly,28–31 post-modification,32–34 or immobilized guest into the pore during self-assembly.35–37

1.2.1.2.1 Metal Clusters as the Catalytic Active Sites in MOFs

Fig 5 a) [Co4Cl]7+ secondary building unit and the crystal structure of Co-btt; b) Epoxides ring opening reaction carried out by Co-btt catalysis.38

Furthermore, the compound [Co(DMA)6]3[(Co4Cl)3(btt)8(H2O)12]·12H2O (Co-btt) was synthesized by the reaction of CoCl2·6H2O and H3btt in DMA solvent Crystal structure revealed that Co-btt was constructed from square-planar [Co4Cl]7+ which connected by triangular tritopic btt3- bridging ligands in order to form the net type

(Figure 5a) Co-btt possesses cobalt active center which could act as Lewis acid as well

as redox-active centers The Lewis acid property of Co-btt was tested by epoxides ring

opening reaction which exhibit the better performance as compare to homogeneous catalyst of Co(NO3)2·6H2O (Figure 5b).38

Recently, the zeolite-imidazole framework, ZIF-9, in the co-catalyst system include [Ru(bpy)3]Cl2·6H2O and triethanolamine (TEOA, electron donor), under mild reaction

conditions (20 °C and 1 atm CO2) with visible-light illumination could exhibit the ability to convert CO2 gas into CO with turnover number (mol(H2+CO)/mol(Co2+)) of

450 after 2.5 hours (Figure 6).39

Fig 6 a) Crystal structure of ZIF-9; b) The CO2 reduction reactions catalysis by ZIF-9.39

1.2.1.2.2 Functional Linkers as Catalytic Active Sites in MOFs

The metallo-linker, which beared porphyrin or salen groups could capture metal to transform into catalytic active centers Subsequently, the linker was employed for MOFs synthesis in order to bring catalytic active centers into the porous framework to serve as the heterogeneous catalyst

Hupp’s group developed a porphyrin-based ligand with pyridine terminal groups, the linker subsequently served as the pillars between two square grid layers which constructed from 1,2,4,5-tetrakis(4-carboxyphenyl)-benzene and paddle zinc SBU to form 3D framework named ZnPO-MOF (Figure 7a) The acyl-transfer reaction was carried out between N-acetylimidazole and 3-pyridylcarbinol, a 2420-fold rate enhancement was observed in the presence of ZnPO-MOF relative to the non-catalyzed reaction The significant enhance of catalytic activity can be assigned to the fitting distance between the metal sites of two porphyrin linker (Figure 7b).29

Fig 7 a) Structure of ZnPO-MOF and corresponding linker to construct the MOF; b)

Mechanism for acyl-transfer reaction catalyze by ZnPO-MOF.29

In attempting to incorporate metal-free catalytic centers into MOF, urea functional groups was employed as the linker backbone in order to construct material, namely, NU-601 Initially, NU-601 was constructed from tetrakis-carboxylate linker and Zn2nodes to form two dimension sheets and following by inserting the pillar 4,4’-bipyridine between two apical sites of paddle wheel zinc SBU in order to form the 3D framework (Figure 8a) The investigation of Friedel-Crafts reaction between N-methylpyrrole and (E)-1-nitroprop-1-ene exhibited better performance of NU-601 as compare to the homogenous diphenyl urea The high catalytic performance of NU-601, which was assumed by the authors, assigned to the fixed arrangement of urea groups which permanently activated the reactant while self-quenching state of urea could take place

in reaction solution (Figure 8b).28

Fig 8 a) Urea MOF strategy; b) Catalytic activities of NU-601.28

1.2.1.2.3 Post-Modification Strategy for Incorporating Catalytic Active Sites into MOFs

Fig 9 a) Post-modified MIL-101 by sequent combination between Brønsted acid and Lewis

acid sites; b) Investigated the benzylation reaction of mesitylene with benzyl alcohol; c) Compared catalytic activity of MIL-101-Cr-SO3H·Al(III) with other catalysts.32

A sequent combination between Brønsted acid and Lewis acid sites into metal organic framework leaded to new type of catalyst, named MIL-101-Cr-SO3H·Al(III) (Figure 9a) According to the authors, the synergy effect between Brønsted acid and

Lewis acid, was assumed for outperforming activity of MIL-101-Cr-SO3H·Al(III) in tested fixed-bed reactions for benzylation of mesitylene was observed Taken note, excellent catalytic activity of MIL-101-Cr-SO3H·Al(III) was even higher and also retained at least 6 hours while traditional zeolite catalysts quickly lost catalytic activity (Figure 9b,c).32

Furthermore, the post-modification of MIL-101-Fe, utilized imine condensation strategy, leaded to new material, named (Ni@(Fe)MIL-101), in which nickel active sites played the catalytic active center for ethylene oligomerization Interestingly, the new material could exhibited very selective against liquid-phase ethylene dimerization

to form 1-butene (Figure 10).34

Fig 10 One-Pot Synthesis of the MIL101-Anchored Nickel Complex, Ni@(Fe)MIL-101.34

1.2.1.2.4 Immobilization of Catalytic Active Guests into MOFs via Assembly

Self-The material, named rho-ZMOF, possessed the anionic pore, which could fix one porphyrin molecule into each cage of material (Figure 11a) Assumed by the authors, that could prevent oxidative self-degradation associated with self-dimerization, naturally found in homogeneous porphyrin catalyst, hence, stabilized catalytic activity

of the system The Mn-metallated porphyrin encapsulated in rho-ZMOF shows high catalytic performance toward the oxidation of cyclohexane and could be recycled up to

11 cycles (Figure 11b).36

Fig 11 a) Crystal structure of rho-ZMOF with schematic presentation of [H2TMPyP]4+porphyrin ring enclosed in rho-ZMOF α-cage, b) Cyclohexane catalytic oxidation at 65 °C Yield % based on TBHP, 1 eq consumed per alcohol produced and 2 eq consumed per ketone produced.36

Immobilizing Keggin-type polyoxometalate (POM), [CuPW11O39]5- into the cage of HKUST-1 leaded to the new type POM@MOF hybrid material Assumed by the authors, this inclusion system resulted in a substantial synergistic stabilization of both the MOF and the POM, and interestingly, enhanced dramatically the catalytic turnover rate of the POM for air-based oxidations Accordingly, POM@MOF could exhibit the rapid chemo- and shape-selective oxidation of thiols to disulfides and, more significantly, the rapid and sustained removal of toxic H2S with very high turnover (4000 turnovers in ≤ 20 h) while the POM or the MOF alone is catalytically slow or inactive (Figure 12).37

Fig 12 X-rays crystal structure of CuPW11O39]5-@HKUST-1.37

1.2.2 Metal-organic Frameworks for Proton Conduction

The development of novel electrolyte materials for proton exchange membrane fuel cells (PEMFCs) has received considerable attention owing to the need for alternative energy technologies However, effectively working condition of PEMFCs was identified at medium temperature (T ≥ 100 °C) under low relative humidity (RH), at which, higher CO tolerance of Pt catalyst was accounted for as well as reducing the associating cost to maintain high RH at T ≥ 100 °C Unfortunately, the current technology, which utilized nafion proton conducting membrane (the key components within HFCs) could not well support for above working condition, hence, the quest to synthesize PEMFCs which can satisfactorily function at medium temperature (T ≥ 100

°C) under low RH was raised as top urgent goal.2

Recently, metal-organic frameworks (MOFs) have been explored as potential candidates for use as electrolyte materials.40 This is primarily due to the modular nature of MOF design and synthesis, in which the backbone components [e.g inorganic and organic secondary building units (SBUs)] can be easily tailored to satisfy particular applications.1 Indeed, previous work on developing MOFs as proton conducting materials have focused on incorporating proton transfer agents within the pores,41–43 functionalizing coordinatively unsaturated metal sites,44,45tuning the acidity of the pore channels through incorporating specific functional

groups,46–51 and controlling and modifying defect sites,52,53 among others.3 These strategies have led to significant developmental progress, in which proton conductivities in MOFs have been achieved on the order of 10-2 S cm-1, but require high working relative humidity (≥ 90% RH) On the other hand, proton conductivity under anhydrous conditions (T ≥ 100 °C) in MOFs has reached ultrahigh levels (10-2 S cm-1), albeit in a limited number of reports

1.2.2.1 Water-mediated Proton Conducting MOFs

The water-mediated proton conducting in MOFs, typically, was found to be Grotthuss mechanism, which addresses the conduction of protons within a hydrogen-bonded network of water molecules Protons are envisaged as forming H3O+ species within a water cluster, with transfer occurring upon concurrent severing of hydrogen-bonds, transfer of the proton and subsequent rearrangement between nearby H2O molecules In this manner, protons ‘‘hop’’ along their conduction pathway through protonation and deprotonation of water molecules Grotthuss mechanism conduction processes generally involve low activation energies (Ea < 0.4 eV).3

Another rarely observed mechanism was found in MOFs is vehicular transportation, which related to transport of larger ionic species (with greater mass compared to H+) and requires a larger activation energy (Ea ≥ 0.4 eV).3

1.2.2.1.1 Design Strategy toward High Proton Conductivity MOFs under Humidity Condition

1.2.2.1.1.1 Doping Proton Donors Molecules into the MOFs

Typically, strong proton donors such as H3PO4, H2SO4 were chosen as the doping agents in order to achieve high conductivity Consequently, the host frameworks need

to have pore size which is large enough for the protogenic agent to diffuse into the pore

as well as maintain the long range structural order and atomistic connectivity after acidic doping Recently, only a few MOFs matched those criteria to serve as the scaffold for acidic immobilization, for examples, the doping system of H2SO4@MIL-101,

H3PO4@ MIL-101 exhibited proton donor’s types and conductivity dependence under

similar condition.43 Additionally, the pH of doping liquor and proton conductivity were found to be dependent, indeed, the conductivity of H2SO4@Ni-MOF-74 could be controlled over the range from 5.3 × 10-4 to 2.2 ×10-2 S cm-1 as varied pH of doping liquor.42 Generally, the conductivity for such systems were compared to some highest values achieved up to now, however, hazards correlating with strong proton donors as well as risk of acids leaching under working condition maintained the key drawbacks for practical implementation of these materials

1.2.2.1.1.2 Coordinately Unsaturated Metal Sites Approach

Commonly, the metal coordinated sites in MOFs were capped by chelated groups

of framework backbone linkers Less commonly, as determined by framework architecture, metal coordinated sites in a few MOFs were chelated by the another ligands such as methanol or water, which resulted in generation of Brønsted acid sites, for example, water could chelate apical sites of copper paddle wheel SBU Rely on the predictable architecture, MOFs could be designed to satisfy the criteria for dense and short distance between Brønsted acid sites to form the conduction pathway

Although, the Brønsted acid sites in MOFs are weak, some conducting systems in MOFs could surpass super proton conducting level (σ > 10-4 S cm-1) Typical conductivity for this systems, for example, Cu-TCPP could approach the magnitude of

10-3 S cm-1 under very high relative humidity.45 Although the Brønsted acid sites located next to each other, these MOFs could not conduct under anhydrous condition as designed very dense and short distance between Brønsted acid sites still maintained challenge Recently, compound [Eu2(CO3)(ox)2(H2O)2]·4H2O that made use of water functionalizing coordinately unsaturated metal sites strategy, could surpass above challenge to approach the conductivity of 2.08 × 10-3 S cm-1 at 150 °C.54

1.2.2.1.1.3 Acidic Functional Groups Approach

Proton conduction in MOFs can emerge from functioning organic linkers with proton donor groups Typically, the linkers that born acidic groups were chosen to target MOFs structure Although post-modification with acid or base functional groups in order to obtain conducting MOFs is promised, rare reports were found for this approach

As incorporating proton donor groups, the resulted architecture can vary from the target framework and not always conducted as the acidic or basic groups could coordinate to metal sites as the extra ligand

The resulted conductivity from above strategy could vary from the magnitude of 10

-4 S cm-1 to 10-2 S cm-1 depended on the MOFs structure and functional groups The highest values is 8 × 10-2 S cm-1 for UiO-66(SO3H)2.46 Water stable MOFs was reported for proton conductivity such as PCMOF-5 which was constructed from lanthanum metal and 1,2,4,5-tetrakisphosphonomethylbenzene with maximum conductivity around 2.5 × 10−3 S cm-1.51

1.2.2.1.1.4 Defect Sites Approach

Recently, investigated the relationship between structural defect within UiO-66 and proton conductivity gained significantly interest.52,53 Taken from investigations,

the level of defect sites within UiO-66 could enhance conductivity of

corresponding sample, in which, the missing linkers were assumed to be replaced by coordinated waters and generated Brønsted acids sites Consequently, the higher ratio

of missing BDC2- linkers inside UiO-66, the higher conductivity was obtained Accordingly, the maximum conductivity of the system could approach 6.9 × 10-3 S cm-

1 as the missing BDC2- was equal to 17%.53

1.2.2.1.1.5 Water-mediated Proton Conductivity of MOFs

Table 1 Published MOFs for water-mediated proton conduction and its conductivity

VNU-15 2.9 × 10 -2 0.22 95 60 This

work

H2SO4@Ni-MOF-74(pH = 1.8) 2.2 × 10-2 0.14 80 95 42

PCMOF21/2 2.1 × 10-2 0.21 85 90 47LiCl@[Ca(C4O4)(H2O)]n 1.0 × 10-2 0.18 25 20 57La(H5DTMP)·7H2O 8 × 10-3 0.25 24 98 58(NH4)2(H2adp)[Zn2(ox)3]·3H2O 8 x 10-3 0.63 25 98 59

Zr6O4(OH)7(BDC)5 6.9 x 10-3 0.22 65 95 53Ca-PiPhtA-NH3 6.6 × 10-3 0.4 24 98 60

MF)69(NO3)2]n 2.3 × 10-3 0.22 25 95 49[Eu2(CO3)(ox)2(H2O)2]·4H2O 2.08 × 10-3 0.28 150 NA 54(NH4)4[MnCr2(ox)6]·4H2O 1.7 × 10-3 0.23 40 96 64

CoII[CrIII(CN)6]2/3·4.8H2O 1.7 × 10-3 0.22 35 100 63MgH6ODTMP·6H2O 1.6 × 10-3 0.31 19 100 65

Fe(Ox)·2H2O 1.3 × 10-3 0.37 25 98 67{[Ca(D-Hpmpc)(H2O)2]·2HO0.5}n 8.9 × 10-4 0.21 60 97 68

K2(H2adp)[Zn2(ox)3]·3H2O 1.2 × 10-4 0.45 25 98 73{NH(prol)3}[MCr(ox)3] 1.0 × 10-4 NA 25 75 74

1.2.2.2 Anhydrous proton-conducting MOFs

On the other hand, proton conductivity under anhydrous conditions (T ≥ 100

°C) in MOFs mainly relied on doping proton carrier guest (e.g pyrazole, triazole, imidazole, etc.) or employed the immobilization of proton carrier as courter cation to the framework backbone, such approaches could reach levels on the order of 10-3 or lower,66,76–78 which is not high enough for practical hydrogen fuel cell.3 In particular cases, for example, doping of Brønsted acid (H2SO4, H3PO4, CF3SO3H) into MOFs could lead to high levels proton conductivity (10-2 S cm-1) under low relative humidity,43 however, several drawbacks have been realized for anhydrous proton conduction in MOFs:

 Evaporating of proton carrier at high temperature which will degrade on conductivity of membrane For example, compound His@[Al(μ2-OH)(1,4-NDC)]n(His = Histamine hydro chloride) was found to significantly lose its conductivity after 4 hours investigation at 130 °C resulting from releasing of histamine.76

 Albeit, lacking of investigations about dependence between proton conductivity over time period to claim for stability of the doping system of strong corrosive acid (H2SO4, H3PO4, CF3SO3H) in MOFs.43 In fact, strong corrosive acids may slowly degrade the host framework as well as leaching out to environment,42 thus make the material non-practical to be utilized in real fuel cells

Recently, the conducting system of DMA@MOFs (DMA= dimethyl ammonium) was found to support proton conduction under anhydrous condition, in fact,

{[(Me2NH2)3(SO4)]2[Zn2(ox)3]}n exhibited maximum conductivity of 1.0 × 10-4 S

cm-1 at 150 °C under anhydrous atmosphere.56

Table 2 Published MOFs for anhydrous proton conduction and its conductivity

[ImH2][Cu(H2PO4)1.5(HPO4)0.5·Cl

H2SO4@MIL-101 1.0 × 10-2 0.42 150 0.13 43CsHSO4@Cr-MIL-101 1.0 × 10-2 NA 200 0 79His@[Al(μ2-OH)(1,4-NDC)]n 1.7 × 10-3 0.25 150 0 76

[Zn(H2PO4)2(TzH)2]n 1.2 × 10-4 0.6 150 0 78{[(Me2NH2)3(SO4)]2[Zn2(ox)3]}n 10-4 0.13 150 0 56

CHAPTER 2: SYNTHESIS OF THE NOVEL METAL-ORGANIC FRAMEWORKS AND MATERIAL CHARACTERIZATIONS

2.1 Introduction

2.1.1 The Modular Nature in Design and Synthesis of MOFs and The Quest

to Design and Synthesize New MOFs

In MOFs chemistry, choice of metals as well as organic linker determined structure and properties of obtained materials The linkers for MOFs usually contain multifunctional chelating organic groups in which the most common are carboxylates,80pyridine,81 imidazole,82 phosphonates and sulfonates,83 among others In addition, the linkers with different functional groups, length and bond angle significantly contributed

to define framework structure and properties (Table 3).84–87

Recently, more than 20.000 different MOFs have been reported Several of these were found to have the capabilities to solve challenge which encountered in modern ages Despite the significant progress in synthesis and applications of MOFs, there are maintained challenges sought to overcome by novel MOFs, which possess novel or enhanced properties, for example, the quest to synthesize better proton conducting membrane that can maintain high conductivity (>10-2 S cm-1) at medium temperature (T ≥ 100 °C) or a demand for larger pore aperture porous material which can serve as host scaffold for various doping of active guest molecules as well as played the catalyst for the transformation of large organic substrates