Zirconium phosphonate structure

Fig. 42.10 Ligands anchored to zirconium phosphonate-layered structures or titanium dioxide particles.

Layered metal IV phosphonates are widely used, particularly zirconium phosphonates, because their synthesis is versatile and their structural arrangement may be tailored to applications. Zirconium phosphonates are usually prepared by heating an aqueous solution of a metal IV salt (e.g., ZrOCl2) with a phosphonic acid at 60-80 °C synthesis in the presence of HP permits one to increase significantly the crystallinity of the final products. 

In contrast to the conventional approach whereby various organic groups are subsequently bound to a previously prepared surface, we have been synthesizing a broad series of anchored, layered-structure solids by precipitating the pre-derived phosphonate salts with tetravalent metal ions. The two-dimensional backbone has the zirconium phosphate structure however, substituted for hydroxylic groups are the desired organics, oriented away from the basal surfaces in a bilayered fashion in the interlayer region. 

Several alternative self-assembly approaches for producing thermally stable, acentric chromophoric multilayers have been reported [142-144]. The most prominent example is that developed by Katz et al. [145,146], which takes advantage of the zirconium phosphonate/phosphate coordinative bonding to fix layers of a dye to one another producing films with a good structural regularity and stability to orientational randomization of up to 150°C. Another example utilizes the electric field-induced LbL assembly technique of ionic species, followed by UV irradiation to convert the ionic bonds between layers into covalent bonds [147],... 

Debashis C, Vadapalli C, Manish B, Ralph K, Roesky WH, Mathias N, et al. Metal aUcoxides as versatile precursors for group 4 phosphonates synthesis and X-ray structure of a novel organosoluble zirconium phosphonate. Inorg Chem 2000 39(l) 23-6. 

Figure 17.11 shows proton conductivity data at 100°C for the 3M ionomer doped with various HP As. Two observations are immediately apparent (1) that the structure and amount of the additive have a strong influence and (2) that the effect becomes dramatically less as the RH is lowered. Similar results are shown for zirconium phosphonate composites with PFSA ionomer [59]. 

Vivani, R. Costantino, U. Nocchetti, M. Crystal engineering on layered zirconium phosphonates crystal structure (from x-ray powder data) and non-covalent interactions on the layered zirconium compound of 4-[bis(phosphonomethyl)amino]butanoic acid. 7. Mater. Chem. 2002, 12, 3254-3260. 

In order to prepare an extended-lattice monolayer, the organization of the surface template layer is the crucial step. For zirconium phosphonate layers, it is found that the LB method produces an organized phosphonic acid surface layer that in turn can be used to produce monolayer or multilayer zirconium phosphonate films. Once the template layer is in place, self-assembling the capping layer generates a zirconium phosphonate bilayer that more closely resembles the solid-state structure than does a bilayer formed by capping the template with another LB film. If the LB template is used to prepare multilayer films, the well-characterized and ordered template layer... 

Figure 1. Schematic drawing of the structure of a-zirconium phosphate and the zirconium phosphonate salts Z C>3PR)2. The water of hydration is eliminated for clarity, and dotted lines indicate the registry of layers in a-Zr(03P0H)2 H20.

Organic phosphonates represent another class of anchoring agents, which react with zirconium hydroxide to form pillared structures. These are also referred to as molecularly engineered layered structures (MELS). Layered compounds of organic phosphonates of zirconium with the formula of Zr(RP03)2 have been rec-... 

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer structures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer structure with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

Zinc [37], manganese [38], molybdenum [34], and vanadium [40,41] also form lamellar structures. For example, molybdenyl phenylphosphonate forms a linear structure with double chains in which the molybdenyl oxygens of the adjacent chains point toward each other and the phenyl groups are on the outside [42], As is the case with zirconium phosphate and phosphonate, the layered nature of the above metal phosphonates is similar to that of the respective phosphates. Among these, vanadium phosphonates have generated greater interest in view of their importance as industrial catalysts. 

Figure 30 Schematic representation of the polar orientation of the dyes in the multilayers of zirconium phosphate-phosphonate interlayers. This scheme is based on the known structures of Zr(H0P03)2 and related organic Zr phosphonate salts. (From Ref. 65a. Copyright 1991 The American Association for the Advancement of Science.)...

Figure 44 Proposed structure of ZrPV(X). Bars represent the phosphonate oxygen and zirconium atoms. (From Ref. 89b. Copyright 1993 The American Chemical Society.)...

The ability to modify the backbones of LMP structures with phosphonates allows for wide flexibility in the design of new materials containing photoactive binuclear metal cores. The goal of our initial studies has been to demonstrate that a ligating functionality within the gallery is accessible for reaction with a bimetallic core. To demonstrate these initial objectives, we have chosen to study zirconium phosphate modified with alkyl carboxylate, which is a good ligand of bimetallic cores. 

Fig. 3 A side view of the layered structure of zirconium bisfphenyl-phosphonate), with edge-to-edge interactions between phenyl rings on neighboring sheets.8 Green spheres denote phosphorus, red oxygen, and gray carbon, with ZrO,. octahedra in blue.

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