Role of aromatic vs. aliphatic amine for the variation of structural, electrical and catalytic behaviors in a series of silver phosphonate extended hybrid solids

Abstract

Four inorganic–organic hybrid silver phosphonate compounds, [Ag(C₁₀H₈N₂)(H₄hedp)] (1), [Ag₂(C₁₀H₈N₂)(H₃hedp)]·2H₂O (2), [C₄H₁₂N₂][Ag₄(H₂hedp)₂] (3) and [C₄H₁₂N₂][Ag₁₀(H₂hedp)₄(H₂O)₂]·2H₂O (4) (H₅hedp = 1-hydroxyethane-1,1-diphosphonic acid), have been prepared by virtue of the variable amine-directed hydrothermal strategy. The subsequent roles of coordinated aromatic amine (4,4′-bipyridine) and coordination-free templated aliphatic amine (piperazine) are studied. The connectivity of the silver ions, diphosphonate units (hedp) and bipyridine moiety can give rise to the one-dimensional structure of 1 and two-dimensional layer structure of 2. In contrast, the silver ions and diphosphonate units are connected to form the tetrameric and pentameric silver cluster units in compound 3 and 4, respectively. Such clusters are rare examples of fundamental building units in the piperazine templated two-dimensional silver based layer structures. The room temperature dielectric studies show the extremely high dielectric permittivity of the amine templated compounds (3 and 4) compared to amine coordinated structures (1 and 2). The synthesized compounds also participate in various heterogenous catalytic reactions acting as active Lewis acid catalysts that are observed for the first time in the amine-templated metal organophosphonates. The observed band gaps and dielectric values suggest that compounds 3 and 4 are more promising candidates for electronic applications, while compounds 1 and 2 are comparatively better Lewis acid catalysts.