Selected Publications


Zirconium Arene-Phosphonates: Chemical and Structural Characterization of 2-Naphthyl- and 2-Anthracenylphophonate Systems

Abstract
Several new zirconium phosphonates incorporating naphthalene and anthracene ring systems and having the general formula Zr(O3PR)1(O3PR')1 [R and R' = −C10H7, −C14H9, −OC4H9, and −OC2H5] have been synthesized. These compounds were chemically characterized using thermal gravimetric analysis (percentage of organic content), infrared spectroscopy (presence of the desired organic functional groups), and solid-state 31P NMR (phosphorus environments), while the structural parameters were determined using X-ray powder diffraction (interlayer d spacings). The d spacings of the zirconium bis(phosphonates) correlate well with a simple predictive model based on the effective length of the organic functional group. The zirconium mixed phosphonates examined are single-phase structures with random mixtures of the organic moieties within the interlayer and possess d spacings that are between those of the two parent zirconium bis(phosphonates).
Reference
Amicangelo, J.C.; Leenstra, W.R. "Zirconium Arene-Phosphonates: Chemical and Structural Characterization of 2-Naphthyl- and 2-Anthracenylphophonate Systems", Inorg. Chem., 2005, 44, 2067.Download PDF

Molecular Modeling of Interlayer Catalytic Sites for Aniline Polymerization in a Zirconium Mixed Phosphonate Phosphate

Abstract
Theoretical modeling of a mixed zirconium 3-carboxypropylphosphonate phosphate system, (O3P(CH2)3COOH)x(O3POH)2-x, is reported both for a series of stoichiometric compounds and for an aniline-intercalated system. Modeling of the interlayer spacing variation of selected stoichiometries of the host series predicts linear behavior for the intermediate compositions (0.5 ≤ x ≤ 1.5) accompanied by a significant contraction at the terminal stoichiometries (x = 0.0 and 2.0). Our results demonstrate that such behavior is a general feature of layered zirconium phosphonates whose pendant groups possess conformational degrees of freedom. For the host-guest series, the results have provided insight into the energetically stable orientations of the aniline molecule within the interlayer. It was found that the most probable geometry was one in which the aniline C2 axis is in a tilted orientation with respect to the zirconium planes for the host systems studied. However, at slightly higher energy, molecular modeling predicts aniline to be in an orientation corresponding to the C2 axis being parallel to the zirconium planes, which would be favorable for the formation of polyaniline within the interlayer. These results are interpreted in the context of experimental findings published earlier.
Reference
Amicangelo, J. C.; Leenstra, W. R.; Rosenthal, G. L. "Molecular Modeling of Interlayer Catalytic Sites for Aniline Polymerization in a Zirconium Mixed Phosphonate Phosphate", Chem. Mater., 2003, 15, 390.Download PDF

Excimer Formation in the Interlayer Region of Arene-Derivatized Zirconium Phosphonates

Abstract
Metal phosphonate systems comprise a fruitful area of research applications in many fields of solid-state inorganic chemistry. The interlayer region of zirconium phosphonates provides an ideal environment for the investigation of the photochemistry and photophysics of molecular species because of the physical constraints and the two-dimensional nature of the environment it provides. A number of studies to date have been focused on the behavior of species interacting with the layered solid. Photophysical behavior of the pendant groups themselves, as part of a zirconium phosph(on)ate system (see graphic in Table of Contents), is a more unusual phenomenon. Because of the long-term impact of these materials in the area of photochemistry and spectroscopy, we have embarked on an exploration of excimer formation in an interlayer environment.
Reference
Amicangelo, J. C.; Leenstra, W. R. "Excimer Formation in the Interlayer Region of Arene-Derivatized Zirconium Phosphonates", J. Am. Chem. Soc., 2003, 125, 14698.Download PDF

Synthesis, Characterization, and Interlayer Distance Study of Zirconium Phosphonates with Stoichiometric Variation of Methyl and p-Aminobenzyl Pendant Groups

Abstract
A new class of layered zirconium mixed phosphonates, zirconium (p-aminobenzyl)phosphonate methylphosphonate, Zr(O3PCH2C6H4NH2)x(O3PCH3)2-x [abbreviated as Zr(pab)x(me)2-x], and its intercalated hydrochloride form, Zr(O3PCH2C6H4NH3Cl)x(O3PCH3)2-x [Zr(pabHCl)x(me)2-x], in a number of stoichiometric pendant group ratios, have been synthesized and characterized. For these materials, thermogravimetric analysis was able to identify and quantify, when present, loss of surface-adsorbed water, HCl units, methyl and p-aminobenzyl groups. 31P NMR indicated evidence of two types of phosphorus environments that tracked the stoichiometry but behaved differently in chemical shift variation (6.7-8.5 and 2.2-8.0 ppm). FT-IR measurements quantitatively accounted for relative mole fraction as the pendant group ratio was varied. Interlayer spacing measurements as a function of the stoichiometric ratio were carried out by XRD and corroborated by molecular mechanics calculations. The calculations show that interlayer pendant group conformations (rotations about the anchoring P-C bond and of the benzenoid ring) are responsible for d-space variational behavior. It is observed that while Vegard’s law is obeyed to some extent, deviation from linearity can be understood in terms of packing forces.
Reference
Leenstra, W. R.; Amicangelo, J. C. "Synthesis, Characterization, and Interlayer Distance Study of Zirconium Phosphonates with Stoichiometric Variation of Methyl and p-Aminobenzyl Pendant Groups", Inorg. Chem., 1998, 37, 5317.Download PDF

A Novel Staged Form of Layered Zirconium Phosphonates with Methyl and p-Aminobenzyl Pendant Groups

Abstract
Zirconium phosphonates, Zr(O3PR)2, are layered compounds whose structure follows the basic structural motif of zirconium phosphate, Zr(O3POH)2. In these compounds, the zirconium atoms form stacked planes held together by the attractive interactions of the R groups that project into the interlayer region from both sides of any given zirconium plane. Mixed zirconium phosphonates, Zr(O3PR)x(O3PR')2-x, can be formed by coprecipitation of the zirconium in the presence of two different phosphonic acids, leading to the formation of a porous material if the two organic groups on the phosphonic acids are sufficiently different in size. These mixed compounds usually contain a random distribution of the organic groups such that all layers have identical stoichiometry. In such systems, the interlayer spacing (d-space) is a function of pendant group stoichiometry, and has a generally linear dependence on component mole fraction.
Reference
Amicangelo, J. C.; Leenstra, W. R. "A Novel Staged Form of Layered Zirconium Phosphonates with Methyl and p-Aminobenzyl Pendant Groups", J. Am. Chem. Soc., 1998, 120, 6181.Download PDF

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