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Thestructure of the nanoporous metal–organic frameworkCu3(BTC)2(BTC = 1,3,5-benzenetricarboxylate)with a variety of molecular guests was studied in situusing single crystal X-ray diffraction. By collecting crystal structuredata for a series of guests within the same host crystal, insightsinto the molecular interactions underpinning guest adsorption processeshave been gained. Adsorption behaviors are influenced strongly byboth enthalpic and entropic thermodynamic, as well as interpore steric(size-exclusion) effects, and we note correlations between guest attributesand these effects. Vapor adsorption measurements revealed a guestuptake capacity inversely proportional to guest size. Correspondingly,structural results show that guests reside in the smallest pores accessibleto them. Interpore steric effects for larger guests cause these tobe excluded from the smallest pores, and this corresponds to lowertotal uptake. Both hydrophilic and lipophilic small guests adsorbfavorably into the 5 Å diameter smallest pore of the material,with the number of guests in these pores dependent on guest size andtheir location, in turn dependent upon both guest–guest interactionsand competition between hydrogen-bonding interactions at the aperturesof the smallest pore and lipophilic interactions at the center ofthe smallest pore. Hydrophilic guests with lone electron pairs interactpreferentially with the coordinatively unsaturated Cu sites of thedesolvated framework, with the number of these depending on stericinteractions between neighboring bound guests and guest flexibility.Guest coordination at the Cu sites has a significant effect on theframework structure, increasing the Cu···Cu distancein the dinuclear unit, with the Cu3(BTC)2unitcell being smaller when guests that do not coordinate with the Cuare present, and in the case of cyclohexane, smaller than for thedesolvated framework. Overall, our comprehensive structural studyreconciles Cu3(BTC)2adsorption properties withthe underlying guest–host and guest–guest interactionsthat gives rise to these. [ABSTRACT FROM AUTHOR]

An ultramicroporous metal–organicframework (MOF) is reportedthat contains 0.35 nm nanotube-like channels with an unprecedentedconcentration of vacant CuIIcoordination sites. The nonintersecting,narrow channels in [Cu3(cdm)4] (cdm = C(CN)2(CONH2)−) align in two perpendiculardirections, structurally resembling copper-doped carbon nanotubeswith CuIIembedded in the walls of the channels. The combinationof ultramicroporosity with the exposed CuIIcoordinationsites gives size-based selectivity of CO2over CH4, based on pore-size distribution and modeling. Neutron powder diffractionand molecular dynamics simulations show the close packing of singlerows of guests within the tubular nanostructure and interaction ofCO2with the exposed metal sites. [ABSTRACT FROM AUTHOR]