Looking into Metal-Organic Frameworks with Solid-State NMR Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for characterization of materials. It can detect local structure around selected atomic nuclei and provide information on the dynamics of these nuclei. In case of metal-organic frameworks, NMR spectroscopy can help elucidate the framework structure, locate the molecules adsorbed into the pores, and inspect and characterize the interactions of these molecules with the frameworks. The present chapter discusses selected recent examples of solid-state NMR studies that provide valuable insight into the structure and function of metal-organic frameworks

On a Possible Role of Dicarboxylate Ions in the Formation of Open-framework Metallophosphates

Three dicarboxylic acids (oxalic, malonic and terephthalic) were investigated as possible pillars in the formation of metallophosphates with extended structures in the presence of 1,2-diaminopropane (DAP) as a structure-directing agent. Only the oxalate ion was proven to be a suitable building block in the formation of hybrid networks. The terephthalate ion seems to possess the ability to be structurally involved in lattice formation, although not in networks of the hybrid type. The malonate ion in this system showed no propensity towards lattice formation, i.e., malonic acid merely exits as an intercalated species inside the 2–D zincophosphate structure. Different pillar-functioning ability has been attributed to structural differences of the three dicarboxylate ions

On a Possible Role of Dicarboxylate Ions in the Formation of Open-framework Metallophosphates

Three dicarboxylic acids (oxalic, malonic and terephthalic) were investigated as possible pillars in the formation of metallophosphates with extended structures in the presence of 1,2-diaminopropane (DAP) as a structure-directing agent. Only the oxalate ion was proven to be a suitable building block in the formation of hybrid networks. The terephthalate ion seems to possess the ability to be structurally involved in lattice formation, although not in networks of the hybrid type. The malonate ion in this system showed no propensity towards lattice formation, i.e., malonic acid merely exits as an intercalated species inside the 2–D zincophosphate structure. Different pillar-functioning ability has been attributed to structural differences of the three dicarboxylate ions

Multinuclear Magnetic Resonance Study on Aluminium Sec-butoxide Chelated with Ethyl Acetoacetate in Various Amounts

Reactive aluminum alkoxide (ASB, aluminium sec-butoxide) was chelated using β-diketone (EAA, ethyl acetoacetate) in order to gain control over rapid hydrolysis in the course of the sol-gel process. Derived chelates were analysed using several NMR spectroscopic techniques: one-dimensional 1H, 13C, 27Al NMR and two-dimensional COSY, HSQC and DOSY. The NMR analysis enabled identification of the formed chelate species, as well as determination of their quantitative relationships. Several complexation products were observed: tris-chelated monomer, Al(EAA)3, bis-chelated dimmer, Al2(OnBu)4(EAA) 2, tris-chelated dimmer, Al2(OnBu)3(EAA)3, tetra-chelated dimmer, Al2(OnBu)2(EAA)4, and monochelated trimer, Al3(OnBu)8(EAA). Of the formed oligomer compounds, this is the first evidence of Al2(OR)3L3 in any alkoxide and β-ketoester or β-diketone combination. Aluminium sec-butoxide and ethyl acetoacetate complexes Al2(OnBu)4(EAA) 2 and Al2(OnBu)2(EAA)4 were also observed for the first time. With the increase of the EAA/ASB ratio the coordination of aluminium shifts towards six, whereas above the EAA/ASB ratio of 2.5 solely six-coordinated aluminium exists. This work is licensed under a Creative Commons Attribution 4.0 International License

Iodide∙∙∙π interactions of perhalogenated quinoid rings in co-crystals with organic bases

First anion∙∙∙π contacts with quinoid rings have been described in novel co-crystals of tetrabromo- and tetrachloroquinone with iodide salts of substituted N-methylpyridinium cations. In seven crystal structures of these co-crystals a centrosymmetric unit I-∙∙∙quinone∙∙∙I- is observed involving close contacts between iodide anions and electron-depleted carbon skeletons of the quinoid rings. However, the salt with N-methyl-4-methylcarboxypyridinium base crystallizes in two polymorphs characterized by O=C∙∙∙quinone∙∙∙C=O interaction instead of I-∙∙∙quinone∙∙∙I- one. A possible charge transfer, suggested by black color of the crystals, is probed by solid-state NMR and IR spectroscopies and analyzed by DFT calculations

A metal-organic framework with ultrahigh glass-forming ability

Glass-forming ability (GFA) is the ability of a liquid to avoid crystallization during cooling. Metal-organic frameworks (MOFs) are a new class of glass formers (1?3), with hitherto unknown dynamic and thermodynamic properties. We report the discovery of a new series of tetrahedral glass systems, zeolitic imidazolate framework?62 (ZIF-62) [Zn(Im2?xbImx)], which have ultrahigh GFA, superior to any other known glass formers. This ultrahigh GFA is evidenced by a high viscosity ? (105 Pa?s) at the melting temperature Tm, a large crystal-glass network density deficit (??/?g)network, no crystallization in supercooled region on laboratory time scales, a low fragility (m = 23), an extremely high Poisson?s ratio (? = 0.45), and the highest Tg/Tm ratio (0.84) ever reported. Tm and Tg both increase with benzimidazolate (bIm) content but retain the same ultrahigh Tg/Tm ratio, owing to high steric hindrance and frustrated network dynamics and also to the unusually low enthalpy and entropy typical of the soft and flexible nature of MOFs. On the basis of these versatile properties, we explain the exceptional GFA of the ZIF-62 systempublishersversionPeer reviewe