Influence of specific interactions on the sorption characteristics of porous complexes of 3d metals with derivatives of 4,4′-diazophenyl

Abstract

Coordination compounds of 3d metals with ligands -azoderivatives of benzidine and 2-hydroxybenzoic acids or 8-hydroxyquinoline -are shown to be characterized by a porous structure capable of absorbing substances of various types. The type of adsorbate is considerably influenced by the specific absorption volume of the complex.Porous coordination compounds (PCC) are widely used as catalysts for a variety of reactions, working solids for sensor structures, sorbents for separating different substances and for storage gases, hydrogen in particular [1][2][3]. In comparison with many "traditional" porous materials, for example carbon or mesoporous siliceous materials, PCC possess a number of advantages. In particular, PCC contain pores of strictly defined size and topology, but it is possible by varying the transition metal ions in the composition of the complex and/or the bonded bridging ligands, it is possible to obtain compounds with required sorbtive or catalytic properties [4]. The key role in determining the absorption characteristic of a PCC is frequently played by the specific interactions of the PCC with the sorbate, which can be determined by the ratio of the size of the pores of the adsorbent and the size of the molecule of the adsorbate (for example, a sample may absorb a large amount of H 2 and O 2 but absorb practically no N 2 and CO [5]) or as the difference in the bonding energy of the different adsorbates, i.e, the specific interaction of the adsorbate and the PCC [6,7]. The interaction of the adsorbate with the coordination compound, the energy of which is comparable with the energetic barrier for conformational reconstruction of the adsorbent, may be explained by the possibility of "breathing" of a complex compound with a porous structure [8,9]. The consequence is that this interaction may play a key role in determining the size of the limiting sorption volume. At the present time in most papers studying the properties of a PCC, the sorption characteristics are determined from the adsorption isotherm for a single sorbate (usually nitrogen), while the numbers of papers in which there is a systematic analysis of the interaction of sorbates of various types with a PCC is quite small [5][6][7][8][9]. In describing the sorption characteristics they are frequently divided into case 1) absorbed into pores formed by a "rigid" crystal structure, 2) absorbed into pores of a "breathing polymer" with a "labile" crystal structure [8], and 3) absorption in points of the crystal structures, formed by non-bonded elements [9]. In case 1 the sorbtion volume of the sorbent is, as a rule, practically independent on the chemical nature of the adsorbate. On the other hand, in cases 2 and 3 the definite volume of the pores depends on the ability of the absorbate to form bonds (e.g., hydrogen bonds) with structural elements of the sorbent, which may facilitate the input of the sorbent molecule in the pores and the dividing of pores. The maximum volume of the pore in case 2 is limited because the structural elements of the s...

Magnetic and Sorption Properties of Supramolecular Systems Based on Pentanuclear Copper(II) 12‐Metallacrown‐4 Complexes and Isomeric Phthalates: Structural Modeling of the Different Stages of Alcohol Sorption

“…The nonclassical alcohol sorption and desorption isotherms29 of 1 and 2 imply that interaction of complexes 1 and 2 with these alcohols results in structural rearrangements, most likely associated with separation of the chains. The maximum sorption capacity is governed not by the total volume of voids as estimated from the X‐ray structure determinations, but by the interplay between the energy of interaction of substrate with structural units of the coordination compound and the energy of interaction of the structural elements within the crystal lattice (in other words, between the force that separates the Cu 5 units and the force that holds them together) 30. Since the N 2 sorption experiments indicated that the desolvated samples of 1 and 2 contained no pores (note that N 2 suffusion without sorption at 77 K is not possible), different host‐guest interaction energies and different crystal lattice energies may be the reason for the differences in the sorption capacities found for compounds 1 and 2 in methanol and ethanol sorption experiments.…”

A Triple‐Decker Heptadecanuclear (CuII)15(CrIII)2 Complex Assembled from Pentanuclear Metallacrowns

“…In any case, from the shape of the absorption isotherms, it may be concluded that interaction of complex 1 with ethanol results in structural rearrangement, probably associated with separation of Cu 15 Cr 2 units. In such case maximal absorption capacity is governed by the interplay between the energy of interaction of substrate with structural units of the coordination compound and the energy of the crystal lattice 21. Nonetheless, the quantity of absorbed alcohol is comparable with the sorption capacity of porous MOFs vs. similar substrates 22…”

Effect of structural and thermodynamic factors on the sorption of hydrogen by metal–organic framework compounds

“…In the absence of specific interactions and of limitations in respect of the accessibility of the pores due to the size of the sorbate molecules analysis of the sorption isotherms of various substances (including nitrogen at 77 K, hydrocarbons and methanol at 298 K) gives very similar values [40]. The possibility of specific interactions is determined by the chemical nature of the sorbate and the surface and by the ability to form chemical (most often hydrogen) bonds between the molecules of the sorbate and the sorbent [41,42]. It is also worth mentioning that in the case where DG for the specific interactions is comparable with DG for the structural or conformational rearrangement of the MOF the adsorption of the substrate can be accompanied by an increase in the volume of the pores (the effect of "breathing" or swelling of the sample).…”