The molecular building block approach was employed effectively to construct a series of novel isoreticular, highly porous and stable, aluminum-based metal–organic frameworks with soc topology. From this platform, three compounds were experimentally isolated and fully characterized: namely, the parent Al-soc-MOF-1 and its naphthalene and anthracene analogues. Al-soc-MOF-1 exhibits outstanding gravimetric methane uptake (total and working capacity). It is shown experimentally, for the first time, that the Al-soc-MOF platform can address the challenging Department of Energy dual target of 0.5 g/g (gravimetric) and 264 cm3 (STP)/cm3 (volumetric) methane storage. Furthermore, Al-soc-MOF exhibited the highest total gravimetric and volumetric uptake for carbon dioxide and the utmost total and deliverable uptake for oxygen at relatively high pressures among all microporous MOFs. In order to correlate the MOF pore structure and functionality to the gas storage properties, to better understand the structure–property relationship, we performed a molecular simulation study and evaluated the methane storage performance of the Al-soc-MOF platform using diverse organic linkers. It was found that shortening the parent Al-soc-MOF-1 linker resulted in a noticeable enhancement in the working volumetric capacity at specific temperatures and pressures with amply conserved gravimetric uptake/working capacity. In contrast, further expansion of the organic linker (branches and/or core) led to isostructural Al-soc-MOFs with enhanced gravimetric uptake but noticeably lower volumetric capacity. The collective experimental and simulation studies indicated that the parent Al-soc-MOF-1 exhibits the best compromise between the volumetric and gravimetric total and working uptakes under a wide range of pressure and temperature conditions.

Metal-organic frameworks (MOFs) are a promising class of porous materials because it is possible to mutually control their porous structure, composition and functionality. However, it is still a challenge to predict the network topology of such framework materials prior to their synthesis. Here we use a new rare earth (RE) nonanuclear carboxylate-based cluster as an 18-connected molecular building block to form a gea-MOF (gea-MOF-1) based on a (3,18)-connected net. We then utilized this gea net as a blueprint to design and assemble another MOF (gea-MOF-2). In gea-MOF-2, the 18-connected RE clusters are replaced by metal-organic polyhedra, peripherally functionalized so as to have the same connectivity as the RE clusters. These metal-organic polyhedra act as supermolecular building blocks when they form gea-MOF-2. The discovery of a (3,18)-connected MOF followed by deliberate transposition of its topology to a predesigned second MOF with a different chemical system validates the prospective rational design of MOFs.

Gaining control over the assembly of highly porous rare-earth (RE) based metal-organic frameworks (MOFs) remains challenging. Here we report the latest discoveries on our continuous quest for highly connected nets. The topological exploration based on the noncompatibility of a 12-connected RE polynuclear carboxylate-based cluster, points of extension matching the 12 vertices of the cuboctahedron (cuo), with 3-connected organic ligands led to the discovery of two fascinating and highly connected minimal edge-transitive nets, pek and aea. The reduced symmetry of the employed triangular tricarboxylate ligand, as compared to the prototype highly symmetrical 1,3,5-benzene(tris)benzoic acid guided the concurrent occurrence of nonanuclear [RE9(μ3-OH)12(μ3-O)2(O2C-)12] and hexanuclear [RE6(OH)8(O2C-)8] carboxylate-based clusters as 12-connected and 8-connected molecular building blocks in the structure of a 3-periodic pek-MOF based on a novel (3,8,12)-c trinodal net. The use of a tricarboxylate ligand with modified angles between carboxylate moieties led to the formation of a second MOF containing solely nonanuclear clusters and exhibiting once more a novel and a highly connected (3,12,12)-c trinodal net with aea topology. Notably, it is the first time that RE-MOFs with double six-membered ring (d6R) secondary building units are isolated, representing therefore a critical step forward toward the design of novel and highly coordinated materials using the supermolecular building layer approach while considering the d6Rs as building pillars. Lastly, the potential of these new MOFs for gas separation/storage was investigated by performing gas adsorption studies of various probe gas molecules over a wide range of pressures. Noticeably, pek-MOF-1 showed excellent volumetric CO2 and CH4 uptakes at high pressures.

Highly connected and edge-transitive nets are of prime importance in crystal chemistry and are regarded as ideal blueprints for the rational design and construction of metal-organic frameworks (MOFs). We report the design and synthesis of highly connected MOFs based on reticulation of the sole two edge-transitive nets with a vertex figure as double six-membered-ring (d6R) building unit, namely the (4,12)-coordinated shp net (square and hexagonal-prism) and the (6,12)-coordinated alb net (aluminum diboride, hexagonal-prism and trigonal-prism). Decidedly, the combination of our recently isolated 12-connected (12-c) rare-earth (RE) nonanuclear [RE(μ-OH)(μ-O)(OC-)] carboxylate-based cluster, points of extension matching the 12 vertices of hexagonal-prism d6R, with 4-connected (4-c) square porphyrinic tetracarboxylate ligand led to the formation of the targeted RE-shp-MOF. This is the first time that RE-MOFs based on 12-c molecular building blocks (MBBs), d6R building units, have been deliberately targeted and successfully isolated, paving the way for the long-awaited (6,12)-c MOF with alb topology. Indeed, combination of a custom-designed hexacarboxylate ligand with RE salts led to the formation of the first related alb-MOF, RE-alb-MOF. Intuitively, we successfully transplanted the alb topology to another chemical system and constructed the first indium-based alb-MOF, In-alb-MOF, by employing trinuclear [In(μ-O)(OC-)] as the requisite 6-connected trigonal-prism and purposely made a dodecacarboxylate ligand as a compatible 12-c MBB. Prominently, the dodecacarboxylate ligand was employed to transplant shp topology into copper-based MOFs by employing the copper paddlewheel [Cu(OC-)] as the complementary square building unit, affording the first Cu-shp-MOF. We revealed that highly connected edge-transitive nets such shp and alb are ideal for topological transplantation and deliberate construction of related MOFs based on minimal edge-transitive nets.

A targeted rare earth ftw-MOF platform offers the potential to assess the effect of pore functionality and size on gas adsorption via ligand functionalization and/or expansion.