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)], ina 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. P-31 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.