Crown Ether Pillared and Functionalized Layered Zirconium Phosphonates:  A New Strategy to Synthesize Novel Ion Selective Materials

Abstract

Crown ethers have been intensively studied during the last 25 years. 1-3 The interest stems not only from the fact that these studies provide unlimited exploration of structural assembly 4,5 but also from the chemical and biological potential of these compounds as ion exchangers 6 and possible agents for transporting ionic species in living tissues. 7 These macrocyclic ligands are noted for their remarkable selectivity toward metal ions making them excellent choices for the separation of metal ions. 8,9 However, one of the major problems encountered in using macrocyclic ligands in separation processes is the loss of very expensive macrocycles in the solution due to their solubility. 10 One way to overcome this problem is to attach the macrocyclic ligands covalently to a solid support. Early efforts to accomplish this chemical bonding involved connecting the carbon framework of the macrocycles to the siloxy component of silica gel. 11,12 However, this method proved to be fraught with preparative difficulties that involves several reaction steps.Metal phosphonates represent a relatively new class of compounds. 13,14 Many of them are layered compounds in which inorganic groups build up the layer backbone while the organic portion protrudes into the interlamellar space. One of the noted characteristics of these compounds is their predictable structure skeletons. 15,16 Other important features are the simple reaction steps required to make them and the ability to affix the various organic groups on a solid support. 17 In this paper, we report our efforts to incorporate crown ethers onto zirconium phosphonate layers. The crown ether precusors used here are 1-aza-15-crown-5 and 1,4,10,13-tetraoxa-7,16diazacyclooctadecane. They were converted to phosphonic acids by a Mannich type reaction, 18 from which a series of bridged and unbridged zirconium phosphonates were synthesized. Kijima 19 recently reported incorporating the macrocyclic species into the R-and γ-zirconium phosphate by intercalation.Brunet et al. 20 and Alberti 14,21 also were able to bind the crown ether covalently to γ-zirconium phosphate by an ester exchange reaction. Our synthesis, however, is a new general approach to react macrocycle phosphonic acids with zirconium, and the products obtained are the first examples of bridged and nonbridged crown ether derivatized zirconium phosphonates prepared by direct reaction rather than ester interchange and therefore may be more general.The preparation is outlined in Scheme 1. Compound 3 was made from phosphonic acid 2 when the ratio of 2 to phosphoric acid was equal to 2. The X-ray diffraction pattern, shown in Figure 1, suggested that it is a layered compound with a d-spacing of 20.0 Å. When the reaction was performed with additional phosphoric acid, a new layered phase, 4, with d-spacing 13.0 Å, was obtained. The structural difference between these two phases was easily identified from their 31 P solid state NMR spectra. The 31 P NMR spectrum of 3 has two main peaks similar to those obtained for zirconium N-(...

Studies on Cage‐Type Tetranuclear Metal Clusters with Ferrocenylphosphonate Ligands

“…The CdÀO distances range from 2.138(5) to 2.642(5) , with an average of 2.258 , close to that of the reported leaflet structure [Cd 4 [18]crown-6). [26] The distance between the bridging oxygen atom O3 and Cd2 is 2.642(5) , which is the longest of all the CdÀO and CdÀN distances.…”

“…Most studies to date have been carried out on phenylphosphonic and alkylphosphonic acids. [23][24][25] Phosphonic acids with other organic functional groups such as azacrown ethers, [26][27][28] amines, [29][30][31] sulfonate/sulfonic acid [32,33] and carboxylate/carboxylic acid groups [34][35][36][37] have been found to be better ligands that can form many complexes with novel structures and properties. Motivated by the current work on functional coordinate materials bearing ferrocene (Fc) groups, we have synthesized a ferrocenylphosphonic acid, and subsequently used it for coordination with metal salts, thus yielding materials displaying both ferrocene and metal-phosphonate properties in conjunction with robust inorganic backbones.…”

Nanomaterials for Environmental Remediation

“…The Clearfield group has achieved an elegant level of molecular sophistication with their design and synthesis of layered metal phosphonates containing pendant macrocyclic ligands, such as crown ethers and azamacrocycles [55]. Once again, in these compounds the metal phosphonate/phosphate forms the structural backbone of the material, while the phosphate hydroxyls and macrocyclic ligands fill the interstitial layers ( Fig.…”

Syntheses and Characterization of One-Dimensional Antimony(III) Diphosphonates: [NH3(CH2)nNH3][Sb{CH3C(O)(PO3)2}] (n=4, 5)

“…The phosphonate chemistry has been of increasing interest due to their potential applications in ion exchange, catalysis and sensors (1)(2)(3)(4). Great efforts have been made in searching for materials with new structure types (5)(6)(7)(8)(9).…”