Structural Landscape and Proton Conduction of Lanthanide 5-(Dihydroxyphosphoryl)isophthalates.

Metal phosphonate-carboxylate compounds represent a promising class of materials for proton conduction applications. This study investigates the structural, thermal, and proton conduction properties of three groups of lanthanide-based compounds derived from 5-(dihydroxyphosphoryl)isophthalic acid (PiPhtA). The crystal structures, solved from X-ray powder diffraction data, reveal that groups , Ln[OP-CH(COO)(COOH)(HO)] (Ln = La, Pr), and , Ln{[OP-CH(COO)(COOH)](HO)}·2HO (Ln = La, Pr, Eu), exhibit three-dimensional frameworks, while group , Ln[OP-CH(COO)(COOH)(HO)] (Ln = Yb), adopts a layered structure with unbonded carboxylic groups oriented toward the interlayer region.