Reaction of β-amino-β-(pyrid-4-yl)acrylonitrile with the aromatic dicarboxaldehydes 9,10-bis(4-formylphenyl)anthracene and terephthalaldehyde affords the dihydropyridyl products ...9,10-bis(4-((3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenyl)anthracene (L1) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene (L2), respectively. In the solid state L1·2.5DMF·3MeOH (SOF-1) crystallizes in the monoclinic space group P21/c and forms a 3D stable supramolecular organic framework via strong N−H···Npy hydrogen bonds and π−π interactions. The material incorporates pyridyl-decorated channels and shows permanent porosity in the solid state. The pore volumes of the desolvated framework SOF-1a calculated from the N2 isotherm at 125 K and the CO2 isotherm at 195 K are 0.227 and 0.244 cm3 g−1, respectively. The N2 absorption capacity of SOF-1a at 77 K is very low, with an uptake of 0.63 mmol g−1 at 1 bar, although saturation N2 adsorption at 125 K is 6.55 mmol g−1 (or 143 cm3 g−1). At ambient temperature, SOF-1a shows significant CO2 adsorption with approximately 3 mol of CO2 absorbed per mole of host at 16 bar and 298 K, corresponding to 69 cm3 g−1 at STP. SOF-1a also adsorbs significant amounts of C2H2, with an uptake of 124 cm3 (STP) g−1 (5.52 mmol g−1) at 1 bar at 195 K. Methane uptake at 195 K and 1 bar is 69 cm3 (STP) g−1. Overall, gas adsorption measurements on desolvated framework SOF-1a reveal not only high capacity uptakes for C2H2 and CO2, compared to other crystalline molecular organic solids, but also an adsorption selectivity in the order C2H2 > CO2 > CH4 > N2. Overall, C2H2(270 K)/CH4(273 K) selectivity is 33.7 based on Henry’s Law constant, while the C2H2(270 K)/CO2(273 K) ratio of uptake at 1 bar is 2.05. The less bulky analogue L2 crystallizes in the triclinic space group P1̅ as two different solvates L2·2DMF·5C6H6 (S2A) and L2·2DMF·4MeOH (S2B) as pale yellow tablets and blocks, respectively. Each L2 molecule in S2A participates in two N−H···O hydrogen bonds between dihydropyridyl rings and solvent DMF molecules. Packing of these layers generates 1D nanochannels along the crystallographic a and b axes which host DMF and benzene molecules. In S2B, each L2 ligand participates in hydrogen bonding via an N−H···O interaction between the N−H of the dihydropyridyl ring and the O of a MeOH and also via an N···H−O interaction between the N center of a pyridine ring and the H−O of a second MeOH molecule. The presence of the L2−HOMe hydrogen bonds prevents ligand−ligand hydrogen bonding. As a result, S2B crystallizes as one-dimensional chains rather than as an extended 3D network. Thermal removal of solvents from S2A results in conversion to denser phase S2C which shows no effective permanent porosity.
The selective capture of carbon dioxide in porous materials has potential for the storage and purification of fuel and flue gases. However, adsorption capacities under dynamic conditions are often ...insufficient for practical applications, and strategies to enhance CO(2)-host selectivity are required. The unique partially interpenetrated metal-organic framework NOTT-202 represents a new class of dynamic material that undergoes pronounced framework phase transition on desolvation. We report temperature-dependent adsorption/desorption hysteresis in desolvated NOTT-202a that responds selectively to CO(2). The CO(2) isotherm shows three steps in the adsorption profile at 195 K, and stepwise filling of pores generated within the observed partially interpenetrated structure has been modelled by grand canonical Monte Carlo simulations. Adsorption of N(2), CH(4), O(2), Ar and H(2) exhibits reversible isotherms without hysteresis under the same conditions, and this allows capture of gases at high pressure, but selectively leaves CO(2) trapped in the nanopores at low pressure.
Metal-organic frameworks (MOFs)--microporous materials constructed by bridging metal centres with organic ligands--show promise for applications in hydrogen storage, which is a key challenge in the ...development of the 'hydrogen economy'. Their adsorption capacities, however, have remained insufficient for practical applications, and thus strategies to enhance hydrogen-MOF interactions are required. Here we describe an anionic MOF material built from In(III) centres and tetracarboxylic acid ligands (H(4)L) in which kinetic trapping behaviour--where hydrogen is adsorbed at high pressures but not released immediately on lowering the pressure--is modulated by guest cations. With piperazinium dications in its pores, the framework exhibits hysteretic hydrogen adsorption. On exchange of these dications with lithium cations, no hysteresis is seen, but instead there is an enhanced adsorption capacity coupled to an increase in the isosteric heat of adsorption. This is rationalized by the different locations of the cations within the pores, determined with precision by X-ray crystallography.
A series of isostructural metal−organic framework polymers of composition Cu2(L)(H2O)2 (L= tetracarboxylate ligands), denoted NOTT-nnn, has been synthesized and characterized. Single crystal X-ray ...structures confirm the complexes to contain binuclear Cu(II) paddlewheel nodes each bridged by four carboxylate centers to give a NbO-type network of 64·82 topology. These complexes are activated by solvent exchange with acetone coupled to heating cycles under vacuum to afford the desolvated porous materials NOTT-100 to NOTT-109. These incorporate a vacant coordination site at each Cu(II) center and have large pore volumes that contribute to the observed high H2 adsorption. Indeed, NOTT-103 at 77 K and 60 bar shows a very high total H2 adsorption of 77.8 mg g−1 equivalent to 7.78 wt% wt% = (weight of adsorbed H2)/(weight of host material) or 7.22 wt% wt% = 100(weight of adsorbed H2)/(weight of host material + weight of adsorbed H2). Neutron powder diffraction studies on NOTT-101 reveal three adsorption sites for this material: at the exposed Cu(II) coordination site, at the pocket formed by three {Cu2} paddle wheels, and at the cusp of three phenyl rings. Systematic virial analysis of the H2 isotherms suggests that the H2 binding energies at these sites are very similar and the differences are smaller than 1.0 kJ mol−1, although the adsorption enthalpies for H2 at the exposed Cu(II) site are significantly affected by pore metrics. Introducing methyl groups or using kinked ligands to create smaller pores can enhance the isosteric heat of adsorption and improve H2 adsorption. However, although increasing the overlap of potential energy fields of pore walls increases the heat of H2 adsorption at low pressure, it may be detrimental to the overall adsorption capacity by reducing the pore volume.
First‐class accommodation: A series of coordination frameworks with different pore sizes (see structure of one; Cu blue, C gray, H white, O red) are prepared from CuII ions and carboxylate ligands of ...various lengths. Comparison of their sorption properties reveals that smaller pores allow higher densities of adsorbed H2, whereas larger pores allow higher maximum H2 storage capacities.
The robust metal−organic framework compound {Zn2(L)·4H2O}∞ I has been synthesized by hydrothermal reaction of ZnCl2 and 4,4‘-bipyridine-2,6,2‘,6‘-tetracarboxylic acid (H4L). Compound I crystallizes ...in a chiral space group, P42212, with the chirality generated by the helical chains of hydrogen-bonded guest water molecules rather than by the coordination framework. Removal of guest water molecules from the crystal affords the porous material, Zn2(L)∞ (II), which has very high thermal stability and is chemically inert. The N2 isotherm of II at 77 K suggests a uniform porous structure with a BET surface area of 312.7 m2/g and a remarkably strong interaction with N2 molecules (βE 0 = 29.6 kJ mol-1). II also exhibits significant gas storage capacities of 1.08 wt % for H2 at 4 bar and 77 K and 3.14 wt % (44.0 cm3/g, 67 v/v) for methane at 9 Bar at 298 K. The adsorption behavior of II toward organic solvent vapors has also been studied, and isotherms reveal that for different solvent vapors adsorption is dominated by two types of processes, absorbate−absorbate or absorbate−absorbent interactions. The adsorption and desorption kinetic processes in II are determined mainly by the molecular size of the guest species and their interaction with the host.
Reaction of magnesium, calcium, strontium, and barium salts with a range of dicarboxylic acids benzene-1,4-dicarboxylic acid (H2BDC), naphthalene-2,6-dicarboxylic acid (H2NDC), ...4,5,9,10-tetrahydropyrene-2,7-dicarboxylic acid (H2TPDC), pyrene-2,7-dicarboxylic acid (H2PDC), 5,10-dihydroanthracene-2,7-dicarboxylic acid (H2DADC) in N,N′-dimethylformamide (DMF) or N,N′-diethylformamide (DEF) in Teflon-lined stainless steel autoclaves produces a range of metal−organic framework materials. Single crystal X-ray analysis has confirmed that the predominant building block in these materials is a chain of metal centers bridged either by carboxylate moieties alone as in M(DMF)(μ-BDC)∞ (M = Mg or Sr), Ca1.5(DEF)(μ-BDC)1.5∞, and Sr(DEF)(OH2)(μ-BDC)∞ or bridged by both carboxylate ligands and DMF/DEF molecules as in M(μ-DMF)(μ-NDC)∞ (M = Ca, Sr, or Ba), M(μ-DEF)(μ-TPDC)∞ (M = Ca or Sr), M(μ-DMF)(μ-DADC)∞ (M = Ca or Sr), and Sr(μ-DEF)(μ-PDC)∞. In contrast, the isomorphous complexes Mg3(DMF)4(μ-NDC)3∞ and Mg3(DEF)4(μ-NDC)3∞ contain centrosymmetric trinuclear moieties in which each pair of cations is bridged by three carboxylate anions with two pendant solvent molecules coordinated to each of the terminal Mg2+ cations. These trinuclear building blocks act as six-connected nodes and generate a tilted α-Po type structure. Eleven of the 12 structures based upon cationic chains adopt a common extended architecture in which the aryldicarboxylate anions link the chains to generate diamond-shaped channels. However, in the material Sr(DMF)(μ-BDC)∞, the chains are linked to generate a hexagonal motif of triangular channels. In all 12 compounds based on cationic chains, the space within the channels is occupied by coordinated solvent molecules, leading to nonporous materials.
The use of transition metal complexes of bridging bidentate ligands to construct predictable, multi-dimensional infinite networks is an area of chemistry which has received ever-increasing attention ...over recent years. This article will review the advances that have been made in this field of research and will illustrate how ligand design and the properties of the transition metal and counter-anion can be used to control network geometry and thus crystal structure. The range of network topologies and structural motifs that have been constructed thus far will be outlined with particular emphasis upon how specific arrays can be prepared via rational design of molecular building-blocks. The unusual phenomenon of interpenetration, or polycatenation, will be discussed and methods to achieve control over this effect will be highlighted.
We have synthesized five new metal-organic coordination polymers incorporating the bent ligand H2hfipbb 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) with different transition metal ions and ...co-ligands via solvothermal reactions to give Zn2(hfipbb)2(py)2·DMF (1), Zn2(hfipbb)2(4,4′-bipy)(H2O) (2), Zn2(hfipbb)2(bpdab)·2DMF (3), Cd2(hfipbb)2(DMF)2·2DMF (4), and Co(hfipbb)(dpp)·MeOH (5) (py = pyridine, 4,4′-bipy = 4,4′-bipyridine, bpdab = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, dpp = 1,3-di(4-pyridyl)propane). Compound 1 displays a 2-fold 2D→2D parallel interpenetrated layer network with one-dimensional (1D) helical channels, while 3 exhibits a three-dimensional pillared helical-layer open framework of α-Po topology based upon binuclear paddlewheel units. In compounds 2 and 5, binuclear motifs with double carboxylate bridges are linked by hfipbb2− ligands into a 1D ribbon, which are further assembled into two-dimensional non-interpenetrated (4,4) layers via bipyridyl co-ligands. However, the different bridging modes of hfipbb2− ligands and the different disposition of the coordinated co-ligands around metal ions result in subtle differences in the final architecture. Thus, 2 is based on a binuclear cluster node, double-stranded hfipbb2− linkers, and single-stranded 4,4′-bipy linkers, while 5 is based on a binuclear cluster node and hfipbb2− and dpp linkers which are both double-stranded. Among these compounds, the Cd(II) complex 4 is possibly the most interesting because it represents a rare example in which metal centers are linked by carboxylate groups into infinite chains further joined together by hfipbb2− spacers to form a 2D network with tubular helical channels. All these coordination polymers exhibit low solvent-accessible volumes. Both 3 and 4 retain structural integrity and permanent microporosity upon evacuation of guest molecules, with hydrogen uptakes of 0.57 and 0.78 wt %, respectively, at 20 bar and 77 K.
Two new three‐dimensional ScIII metal–organic frameworks {Sc3O(L1)3(H2O)3⋅Cl0.5(OH)0.5(DMF)4(H2O)3}∞ (1) (H2L1=1,4‐benzene‐dicarboxylic acid) and {Sc3O(L2)2(H2O)3(OH)(H2O)5(DMF)}∞ (2) ...(H3L2=1,3,5‐tris(4‐carboxyphenyl)benzene) have been synthesised and characterised. The structures of both 1 and 2 incorporate the trinuclear trigonal planar Sc3(O)(O2CR)6 building block featuring three ScIII centres joined by a central μ3‐O2− donor. Each ScIII centre is further bound by four oxygen donors from four different bridging carboxylate anions, and a molecule of water located trans to the μ3‐O2− donor completes the six coordination at the metal centre. Frameworks 1 and 2 show high thermal stability with retention of crystallinity up to 350 °C. The desolvated materials 1 a and 2 a, in which the solvent has been removed from the pores but with water or hydroxide remaining coordinated to ScIII, show BET surface areas based upon N2 uptake of 634 and 1233 m2 g−1, respectively, and pore volumes calculated from the maximum N2 adsorption of 0.25 cm3 g−1 and 0.62 cm3 g−1, respectively. At 20 bar and 78 K, the H2 isotherms for desolvated 1 a and 2 a confirm 2.48 and 1.99 wt % total H2 uptake, respectively. The isosteric heats of adsorption were estimated to be 5.25 and 2.59 kJ mol−1 at zero surface coverage for 1 a and 2 a, respectively. Treatment of 2 with acetone followed by thermal desolvation in vacuo generated free metal coordination sites in a new material 2 b. Framework 2 b shows an enhanced BET surface area of 1511 m2 g−1 and a pore volume of 0.76 cm3 g−1, with improved H2 uptake capacity and a higher heat of H2 adsorption. At 20 bar, H2 capacity increases from 1.99 wt % in 2 a to 2.64 wt % for 2 b, and the H2 adsorption enthalpy rises markedly from 2.59 to 6.90 kJ mol−1.
It's ScIIIandalous: {Sc3O(L1)3(H2O)3⋅Cl0.5OH0.5(DMF)4(H2O)3}∞ (1) (H2L1=1,4‐benzenedicarboxylic acid) and {Sc3O(L2)2(H2O)3OH(H2O)5(DMF)}∞ (2) (H3L2=1,3,5‐tris(4‐carboxyphenyl)benzene) incorporate the trinuclear trigonal planar Sc3(O)(O2CR)6 building block. After appropriate thermal treatment on the acetone‐exchanged sample 2, the generation of free metal coordination sites has been achieved to give an increase in the BET surface area in 2 b.
