Enhancing Order and Porosity in a Highly Robust Tin(IV) Triphosphonate Framework

Metal organic frameworks (MOFs) are noted for crystallinity, stability, and porosity. For many industrial challenges though, beyond stability to pore activation, porous materials require high thermal and moisture stability. Here, we report a Sn­(IV) triphosphonate framework, CALF-28, that is highly robust and porous. CALF-28 was designed based on the known structure of a divalent metal phosphonate that was 2-fold interpenetrated. It has strong sustaining interactions but consequently rapidly precipitates, compromising crystallinity. Using methods to enhance order, and by analogy to the M­(II) analogue, insights to the structure are ascertained and corroborated by PXRD and gas sorption analysis. CALF-28 has a surface area >500 m²/g and is stable in water

A Water-Stable Metal–Organic Framework with Highly Acidic Pores for Proton-Conducting Applications

Metal–organic framework (MOF) materials are a nontraditional route to ion conductors, but their crystallinity can give insight into molecular-level transport mechanisms. However, some MOFs can be structurally compromised in humid environments. A new 3D metal–organic framework, PCMOF-5, is reported which conducts protons above 10^–3 S/cm at 60 °C and 98% relative humidity. The MOF contains free phosphonic acid groups, shows high humidity stability, and resists swelling in the presence of hydration. Channels filled with crystallographically located water and acidic groups are also observed

Design of a Humidity-Stable Metal–Organic Framework Using a Phosphonate Monoester Ligand

Phosphonate monoesters are atypical linkers for metal–organic frameworks, but they offer potentially added versatility. In this work, a bulky isopropyl ester is used to direct the topology of a copper­(II) network from a dense to an open framework, CALF-30. CALF-30 shows no adsorption of N₂ or CH₄ however, using CO₂ sorption, CALF-30 was found to have a Langmuir surface area of over 300 m²/g and to be stable to conditions of 90% relative humidity at 353 K owing to kinetic shielding of the framework by the phosphonate ester

Design of a Humidity-Stable Metal–Organic Framework Using a Phosphonate Monoester Ligand

Phosphonate monoesters are atypical linkers for metal–organic frameworks, but they offer potentially added versatility. In this work, a bulky isopropyl ester is used to direct the topology of a copper­(II) network from a dense to an open framework, CALF-30. CALF-30 shows no adsorption of N₂ or CH₄ however, using CO₂ sorption, CALF-30 was found to have a Langmuir surface area of over 300 m²/g and to be stable to conditions of 90% relative humidity at 353 K owing to kinetic shielding of the framework by the phosphonate ester

A Water-Stable Metal–Organic Framework with Highly Acidic Pores for Proton-Conducting Applications

Metal–organic framework (MOF) materials are a nontraditional route to ion conductors, but their crystallinity can give insight into molecular-level transport mechanisms. However, some MOFs can be structurally compromised in humid environments. A new 3D metal–organic framework, PCMOF-5, is reported which conducts protons above 10^–3 S/cm at 60 °C and 98% relative humidity. The MOF contains free phosphonic acid groups, shows high humidity stability, and resists swelling in the presence of hydration. Channels filled with crystallographically located water and acidic groups are also observed

Single Crystal Proton Conduction Study of a Metal Organic Framework of Modest Water Stability

A sulfonated indium (In) metal organic framework (MOF) is reported with an anionic layered structure incorporating hydrogen-bonded dimethylammonium cations and water molecules. The MOF becomes amorphous in >60% relative humidity; however, impedance analysis of pelletized powders revealed a proton conduction value of over 10^–3 S cm^–1 at 25 °C and 40% RH, a very high proton conduction value for low humidity and moderate temperature. Given the modest humidity stability of the MOF, triaxial impedance analyses on a single crystal was performed and confirmed bulk proton conductivity over 10^–3 S cm^–1 along two axes corroborating the data from the pellet

Zn₇O₂(RCOO)₁₀ Clusters and Nitro Aromatic Linkers in a Porous Metal–Organic Framework

A new metal–organic framework, CALF-22 comprising Zn₇O₂(COO)₁₀ secondary building units and 2-nitro-1,4-benzenedicarboxylate, is reported. The porosity and gas adsorption of N₂, H₂, CO₂, and CH₄ are studied, and CALF-22 has a surface area in excess of 1000 m²/g. The stability of the larger zinc cluster and the effect of the nitro group on gas sorption are also studied

A Water Stable Magnesium MOF That Conducts Protons over 10^–2 S cm^–1

From the outset of the study of MOFs as proton conductors, both conductivity and hydrolytic robustness of the materials have needed to be improved. Here, we report a layered magnesium carboxyphosphonate framework, PCMOF10, that shows an extremely high proton conductivity value of 3.55 × 10^–2 S·cm^–1 at 70 °C and 95% RH. Moreover, PCMOF10 is water stable owing to strong Mg phosphonate bonding. The 2,5-dicarboxy-1,4-benzenediphosphonic acid (H₆L) linker anchors a robust backbone and has hydrogen phosphonate groups that interact with the lattice water to form an efficient proton transfer pathway

A Water Stable Magnesium MOF That Conducts Protons over 10^–2 S cm^–1

From the outset of the study of MOFs as proton conductors, both conductivity and hydrolytic robustness of the materials have needed to be improved. Here, we report a layered magnesium carboxyphosphonate framework, PCMOF10, that shows an extremely high proton conductivity value of 3.55 × 10^–2 S·cm^–1 at 70 °C and 95% RH. Moreover, PCMOF10 is water stable owing to strong Mg phosphonate bonding. The 2,5-dicarboxy-1,4-benzenediphosphonic acid (H₆L) linker anchors a robust backbone and has hydrogen phosphonate groups that interact with the lattice water to form an efficient proton transfer pathway

Enhancing Water Stability of Metal–Organic Frameworks via Phosphonate Monoester Linkers

A new porous metal–organic framework (MOF), barium tetraethyl-1,3,6,8-pyrenetetraphosphonate (CALF-25), which contains a new phosphonate monoester ligand, was synthesized through a hydrothermal method. The MOF is a three-dimensional structure containing 4.6 Å × 3.9 Å rectangular one-dimensional pores lined with the ethyl ester groups from the ligand. The presence of the ethyl ester groups makes the pores hydrophobic in nature, as determined by the low heats of adsorption of CH₄, CO₂, and H₂O (14.5, 23.9, and 45 kJ mol^–1, respectively) despite the polar and acidic barium phosphonate ester backbone. The ethyl ester groups within the pores also protect CALF-25 from decomposition by water vapor, with crystallinity and porosity being retained after exposure to harsh humid conditions (90% relative humidity at 353 K). The use of phosphonate esters as linkers for the construction of MOFs provides a method to protect hydrolytically susceptible coordination backbones through kinetic blocking