Highly Selective Ferric Ion Sorption and Exchange by Crystalline Metal Phosphonates Constructed from Tetraphosphonic Acids

Abstract

With the motivation of searching for highly selective ferric ion sorbents, two open-framework and microporous materials, {[Pb7(HEDTP)2(H2O)] x 7H2O}n (1) and {[Zn2(H4EDTP)] x 2H2O}n (2) [H8EDTP = N,N,N',N'-ethylenediaminetetrakis(methylenephosphonic acid)], have been synthesized and structurally characterized. The structure of compound 1 results from the seven crystallographically different lead atoms that are bridged by two HEDTP(7-) ligands to yield a three-dimensional microporous framework with tunnels along the a and b axes. Compound 2 features a layer architecture built of square waves along the a axis. The layers are connected by hydrogen bonds between uncoordinated phosphonate oxygen atoms to form a three-dimensional supramolecular network, with one-dimensional tunnels along the a axis. Both compounds 1 and 2 exhibited high ion sorption and exchange capacities for millimolar concentrations of Fe(III). Specifically, when 0.01 g of 1 (or 2) was added to 5 mL of a 1 mM metallic chloride aqueous solution and the mixture was allowed to stand for 2 days at room temperature, compound 1 adsorbed nearly 100% of Fe(III) and compound 2 adsorbed 96.8% of Fe(III). They were also found to adsorb ferric ions selectively over other metal ions, such as Ca(II), Cr(II), Mn(II), Cu(II), Zn(II), Cd(II), etc. Their special ferric ion uptake capacities may be attributed to the cation exchange, coordination bonding, and electrostatic attraction between ferric ions and metal phosphonates.

Structural variations of SnII pyridylphosphonates influenced by an uncommon Sn–N interaction

“…In both of these types of compounds, the inorganic units are covalently bound to the organic moieties of the structure, which can also contain other functional groups. Hybrid materials show great potential in a variety of applications including gas storage [14,15], gas separations [16], catalysis [13,17,18], and ion exchange [19]. The viability of most of these applications depends on the nanoscale structural characteristics of the material.…”

A detailed comparative structural study of the hydrogen bonded networks in solids, obtained by the reaction of 4,4′-bipyridine and varied alkane-α,ω-diphosphonic acids

“…7, 8 and 9). The corresponding D⋯A distances lie between 2.521 (6) cations within the structures discussed here exhibit an almost coplanar conformation of the two pyridinium moieties with a maximum angle of torsion of 2.9(3)°concerning the twist of the two pyridinium rings. All other intramolecular bond lengths and angles of the cations are within the expected ranges.…”

A comparative structural study of alkane- α,ω-diphosphonic acids

“…For undecane-1,11-diphosphonic acid, the powder pattern showed the peaks of two concomitant polymorphs (Figure 7) which were both characterised by single crystal X-ray diffraction. 4 4.464(2); 4.628(2) (H 2 O 3 P) 2 (CH 2 ) 8 4.534(10); 4.578(10) (H 2 O 3 P) 2 (CH 2 ) 12 4.443(2); 4.513 (2) Type 3 d(P···P) [Å] (H 2 O 3 P) 2 (CH 2 ) 7 4.7796(12); 4.7796(12) (H 2 O 3 P) 2 (CH 2 ) 9 4.7798(13); 4.7798(13) (H 2 O 3 P) 2 (CH 2 ) 11 4.7858(10); 4.7858 (10) As a result of our structural investigations, it is now possible to understand the progression of the alkane-α,ω-diphosphonic acids' melting points ( Figure 10). We were able to relate the overall lower melting points of the oddnumbered diphosphonic acids to a looser packing within the hydrophilic regions of the crystal structures (Table 3).…”

“…Especially under acidic conditions, diphosphonic acids show a metal-complexing ability for actinide and lanthanide ions which exceeds that of the analogous carboxylic acids by several orders of magnitude [2][3][4]. Metal phosphonates have got potential applications regarding catalysis [5][6][7][8], ion exchange [9][10][11], proton conductivity [12][13][14][15], intercalation chemistry [16][17][18][19], photochemistry [20][21][22][23][24][25][26] and materials chemistry [27][28][29][30][31]. The strategy of using diphosphonic acids as tectons for the construction of void-containing metal phosphonates has been introduced by Dines et al as early as 1983 [32].…”