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 P-31 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).