“Breathing” in Adsorbate‐Responsive Metal Tetraphosphonate Hybrid Materials

Abstract

The structures of various layered calcium tetraphosphonates (CaH6DTMP; H8DTMP=hexamethylenediamine tetrakis(methylenephosphonic acid)), have been determined. Starting from CaH6DTMP.2H2O, thermal treatment and subsequent exposure to NH3 and/or H2O vapors led to four new compounds that showed high storage capacity of guest species between the layers (up to ten H2O/NH3 molecules) and a maximum volume increase of 55 %. The basic building block for these phosphonates consists of an eight-membered ring chelating Ca2+ through two phoshonate groups, and the organic ligand is located within the layers, which are held together by hydrogen bonds. The structural analysis revealed that the uptake/removal of guest species (H2O and NH3) induces significant changes in the framework not only by changing the interlayer distances but also through important conformational changes of the organic ligand. An anisotropic breathing motion could be quantified by the changes of the unit-cell dimensions and ligand arrangements in four crystalline derivatives. Complete characterization revealed the existence of interconversion reactions between the different phases upon gas uptake and release. The observed behavior represents, to the best of our knowledge, the first example of a breathing-like mechanism in metal phosphonates that possess a 2D topology.

CuII Frameworks from Di‐2‐pyridyl Ketone and Benzene‐1,3,5‐triphosphonic Acid

“…Figure S7 in the Supporting Information) and thus the superexchange through this group can be considered negligible. [41] In contrast to the negative value of J 1 for 2, the corresponding J value for [Cu 4 {py 2 C(OH)O} 2 (AcO) 6 ] [39] was found to be positive (+17.70 cm 6 ]. [39] The positive J value for [Cu 4 {py 2 C(OH)O} 2 (AcO) 6 ] is probably due to the counter-complementarity effect of the syn,syn-carboxylate bridge, which diminishes the antiferromagnetic effect of the alkoxo bridge, [32] something that was not realised in ref.…”

“…[41] In contrast to the negative value of J 1 for 2, the corresponding J value for [Cu 4 {py 2 C(OH)O} 2 (AcO) 6 ] [39] was found to be positive (+17.70 cm 6 ]. [39] The positive J value for [Cu 4 {py 2 C(OH)O} 2 (AcO) 6 ] is probably due to the counter-complementarity effect of the syn,syn-carboxylate bridge, which diminishes the antiferromagnetic effect of the alkoxo bridge, [32] something that was not realised in ref. [39] Similarly to the additional syn,syn-R-PO 3 H -group that bridges the non-magnetic orbitals of two neighbouring Cu II ions in 2 (the syn,syn-phosphonate O atoms are at the apical positions of the Cu II centres), there is a second syn,syn-acetate in [Cu 2 {(py) 2 C(OH)O}(AcO) 2 ] + bridging the non-magnetic orbitals of the Cu II ions within the dinuclear unit (those on the Jahn-Teller axes of both Cu II ions, as shown by the dashed lines in Figure S7 in the Supporting Information).…”

“…The structure of the latter comprises the cationic [Cu{py 2 C(OH) 2 } 2 ] 2+ complex [py 2 C(OH) 2 is the hydrate of py 2 CO], the dianion of benzene-1,3,5-triphosphonic acid (H 4 btp 2-) and water solvates. The magnetic properties of the coordination polymer were rationalized on the basis of magnetically isolated [Cu On the other hand, metal phosphonates [4] have been studied since the 1970s and have been shown to be versatile materials for a range of applications, including intercalation chemistry, [5] ion-exchange reactions, [6] solid-state proton conductivity [7] and heterogeneous catalysis. [8] It is worth noting that none of these applications strictly demands porous materials.…”

“…[14] The advantages of phosphonate-based MOFs over the carboxylate-based MOFs and ZIFs are their enhanced chemical and thermal stability, which are due to the stronger M-O 3 PR bond and their extremely low solubility. To this end, and in the context of exploring new functional materials, phosphonate-based coordination polymers and MOFs have attracted tremendous interest due to their unique structural features and potential applications in various fields, including ion exchange, [6,15] catalysis, [16] adsorption and separation, [16] proton conductivity, [17] water treatment, [15,18] biotechnology, [15,16] photochemistry, [19] dental medicine, [16] cancer treatment, [16] bone disease treatment, [20] magnetism [16,21] and magnetic refrigeration. [22][23][24] It has been proven that the structural variability of metal phosphonates can be increased by the introduction of auxiliary ligands that can coordinate to the metal ions.…”

Syntheses, structures, thermal stabilities and luminescence of two new 3D zinc phosphonates

“…During the last five years, metal phosphonates with fascinating structures and properties have continuously emerged as follows [2,3]. Phosphonic acids with additional functional groups like NH 2 , OH, COOH, pyridyl, imidazole, triazole, thienyl and benzimidazol exhibit many coordination modes to form numerous solids, such as layered calcium tetraphosphonates undergoing a swelling upon NH 3 /H 2 O uptake, Co(2-pmp)(H 2 O) 2 showing reversible changes of structures and magnetic behaviors upon the dehydration-hydration process, as well as porous heterometal phosphonate with helical channels and hydrogen sorption ability [4][5][6][7][8][9][10][11][12][13]. The combination of copper-bipyrimidine and molybdophosphonate clusters results in many hybrid materials [14].…”