RESUMEN
A new gadolinium(III)-pyridine-2,5-dicarboxylic acid (GdIII-2,5-H2pdc)-based three-dimensional coordination polymer, namely, poly[dimethylazanium [bis(µ-pyridine-2,5-dicarboxylato)gadolinium(III)]], {[(CH3)2NH2][Gd(C7H3NO4)2]}n, CP-1, has been synthesized via a typical solvothermal method. The as-synthesized material was characterized in the solid state using single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis and FT-IR spectroscopy. During the synthesis of CP-1, the in situ dimethylformamide (DMF) promotes the formation of a dimeric unit and these act as secondary building blocks in the assembly of a three-dimensional anionic {[Gd(pdc)2]-}∞ framework. The framework has channels along the c axis which are filled by dimethylazanium cations. Interestingly, the framework shows a helical-type assembly running down the a axis. A Hirshfeld surface analysis of CP-1 suggests that extra stability is provided by hydrogen-bonding interactions. The magnetic properties of CP-1 showed weak antiferromagnetic couplings between adjacent Gd3+ ions.
RESUMEN
All 21 [n]-azacubanes are proposed by theoreticians to be stable, however, to-date only the synthesis of 1,4-diazacubane has been reported - as a Ni2+ templated Kagome metal organic framework (MOF). Described herein is the structural reassignment of this Kagome MOF on the basis of deducing the precise experimental procedure, and demonstrating that rather than the formation of 1,4-diazacubane, charge is balanced by disordered piperazinium cations across a twelve-fold symmetry site. Furthermore, quantum chemical calculations reveal that 1,4-diazacubane is unlikely to form under the reported conditions due to unfavorable enthalpies for select hypothetical reactions leading to such a product. This significant structure correction upholds the unconquered synthesis status quo of azacubane.
RESUMEN
Protonation of trans-1,2-bis(4-pyridyl)ethylene (4,4'-bpe) with dilute sulfuric acid (33 %) afforded a protonated adduct [{4,4'-bpeâ 2 H+ }2 {HSO4 }-2 {SO4 }-2 {H2 O}2 ] (1). The neighboring olefinic bond in 1 is in a suitable range (3.931-4.064â Å) to undergo a photochemical [2+2] cycloaddition reaction. Upon irradiation with UV light (365â nm), 1 undergoes a molecular sliding involving the 4,4'-bpeâ 2 H+ units, affording 2, stabilized through OSO4 â â â π interactions. Heating 1 to 50° C leads to a 3D hydrogen-bonded organic framework (HOF) (3). This process occurs through thermal dissociation of the bisulfate anion. Diffusion of iodine through the crystal lattice of 1 and 3 enables the reduction of sulfate to bisulfate, affording a 1D hydrogen-bonded chain (4). Solid-state 13 C CPMAS NMR, IR, DSC, and powder XRD studies further support stimuli-responsive structural tuning through crystal-to-crystal transformation. All these conversions occur with significant translational and rotational movements along with a series of bond-breaking and bond-forming processes.