Polymorphic Coordination Networks Responsive to CO₂, Moisture, and Thermal Stimuli: Porous Cobalt(II) and Zinc(II) Fluoropyrimidinolates

Abstract

The novel porous [{M(F-pymo)(2)}(n)]2.5n H(2)O coordination networks (M=Co, Zn; F-pymo=5-fluoropyrimidin-2-olate), possessing sodalitic topology, have been synthesised and structurally characterised by means of powder diffraction methods. Thermodiffractometry demonstrated their plasticity: when heated up to 363 K, they reversibly transform into three-dimensional dehydrated [{M(F-pymo)(2)}(n)] species, with significantly different lattice parameters. Further heating induces irreversible polymorphic transformations into layered phases, in which the original MN(4) coordination sphere changes into an MN(3)O one. A mixed-metal phase, [{Co(x)Zn(1-x)(F-pymo)(2)}(n)]2.5n H(2)O, was also prepared, showing that zinc is preferentially inserted, when starting from a Co/Zn reagent ratio of 1:1. The solid-gas adsorption properties of the anhydrous 3D frameworks have been explored towards N(2), H(2) (77 K) and CH(4), CO(2) (273 K). These results show that these materials permit the diffusion of CO(2) molecules only. Remarkably, the CO(2) adsorption process for the [{Co(F-pymo)(2)}(n)] network proceeds in two steps: the first step takes place at low pressures (<600 kPa) and the second one above a threshold pressure of 600 kPa. By contrast, the [{Zn(F-pymo)(2)}(n)] network only permits CO(2) diffusion by applying pressures above 900 kPa. This type of behaviour is typical of porous networks with gated channels. The high CO(2) selectivity of these systems over the rest of the essayed probe gases is explained in terms of flexibility and polarity of the porous network. Finally, the magnetic studies on the Co(II) systems reveal that the as synthesised [{Co(F-pymo)(2)}(n)]2.5n H(2)O material behaves as an antiferromagnet with a T(N) of about 29 K. At variance, the [{Co(F-pymo)(2)}(n)] layered phase shows an unusually weak ferromagnetic ordering below 17 K, arising from a spin-canting phenomenon.

Carbon Dioxide Capture: Prospects for New Materials

“…From these examples, it is evident that the breathing behavior of flexible frameworks is highly dependent on cooperative effects which arise from the favorable interaction between the quadrupolar CO 2 molecule with the polar surface of the framework. For example, the frameworks [M(F‐pymo) 2 ] (M=Co, Zn, F‐pymo=5‐fluoropyrimidin‐2‐olate) were shown to exhibit highly selective adsorption of CO 2 over CH 4 due to preferential CO 2 interactions with the fluorine groups 121. Highly selective CO 2 capture (over N 2 , H 2 , and CH 4 ) has also been observed in the flexible frameworks [(Ni 2 L)(bptc)], where Ni 2 L represents the ethyl‐ (L1) or butyl‐bridged (L2) Ni 2+ bismacrocyclic complexes and bptc is 1,1′‐biphenyl‐3,3′,5,5′‐tetracarboxylate (Figure 5 b).…”

Abscheidung von Kohlendioxid: Perspektiven für neue Materialien

“…Die Öffnung flexibler Gerüste hängt also stark von kooperativen Effekten ab, die aus günstigen Wechselwirkungen zwischen den quadrupolaren CO 2 ‐Molekülen und der polaren Oberfläche des Gerüsts resultieren. So adsorbieren die Gerüste [M(F‐pymo) 2 ] (M=Co, Zn; F‐pymo=5‐Fluorpyrimidin‐2‐olat) wegen günstiger Wechselwirkungen von Kohlendioxid mit den fluorierten Liganden hochselektiv CO 2 bei Anwesenheit von CH 4 121. Eine hochselektive Abscheidung von CO 2 (in Gegenwart von N 2 , H 2 und CH 4 ) wurde auch für die flexiblen Gerüste [(Ni 2 L)(bptc)] nachgewiesen.…”

Metalorganic frameworks based on the 1,4-bis(5-tetrazolyl) benzene ligand: The Ag and Cu derivatives

“…For example, using substituted triazines [4], bisimidazolates [5] and other substituted heterocycles [6], we have isolated and fully characterised several highly functional materials, such as catalytically active species (soluble oligomers [7] and insoluble 3D polymers [8]) or extended solids capable of molecular sensing and recognition [3,9]. Since many of these materials do not afford single crystals of suitable quality, we attained their full structural characterisation resorting to state-ofthe-art powder diffraction methods, occasionally coupled to thermodiffractometry [10] and 13 C CP-MAS NMR spectroscopy [11].…”