Structural variability of pendant groups within the interlayer region of zirconium arene-phosph(on)ates: chemical and structural characterization of oxy- and methyl-linked 2-naphthyl phosphonates, and mixed oxy-linked derivatives

Abstract

Several new zirconium phosphonates incorporating the naphthalene ring and having the general formula Zr(O₃PR)₁(O₃PR′)₁ [R and R′ = –CH₂C₁₀H₇, –OC₁₀H₇, –CH₃, –OC₂H₅, –OH] have been synthesized. These materials 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 two new zirconium bis(phosphonates), Zr(O₃PC₁₀H₇)₂ and Zr(O₃PCH₂C₁₀H₇)₂, were found to have d spacings of 19.6 and 20.0 Å, respectively. Three of the four zirconium mixed phosphonates examined are found to be single-phase structures with random mixtures of the organic moieties within the interlayer, and possess d spacings (14.3, 15.3, and 16.1 Å) that are between those of the two parent zirconium bis(phosphonates). The fourth is found to be a staged or segregated structure and possesses a d spacing that is approximately a sum of the two parent zirconium bis(phosphonates), with a d spacing of 28.2 Å. Solid-state ³¹P NMR of Zr(O₃PCH₂C₁₀H₇)₂ revealed the presence of two isotropic resonances, which is interpreted in terms of two distinct, “locked-in” conformations of the –CH₂C₁₀H₇ group. The experimental d spacings of the zirconium bis(phosphonates) correlate well with a simple predictive model based on the effective length and predominant conformation of the organic functional group.