Synthesis, structure and optical properties of rare-earth benzene carboxylates

Abstract

Two series of rare-earth isophthalates of the general formula, [M₂(H₂O)] [{C₆H₄(COO)₂}₂{C₆H₄(COOH)(COO)}₂]·H₂O, M = La (I), Pr (Ia), and Nd (Ib) and [M₂(H₂O)₂][{C₆H₄(COO)₂}₃]·H₂O, M = Y (II), Gd (IIa), and Dy (IIb) have been prepared by the reaction of the corresponding trivalent lanthanide salts and isophthalic acid under mild hydrothermal conditions. The La (I), Pr (Ia) and Nd (Ib) have MO₉ polyhedra connected to the isophthalate anions forming a two-dimensional structure, whereas Y (II), Gd (IIa) and Dy (IIb) have MO₇ and MO₈ polyhedral units connected to the isophthalate anions forming a different, but related two-dimensional structure. Both the structures are stabilized by hydrogen bonding and π···π/CH···π interactions. Partial substitution of Eu and Tb (2 and 4%) at the La (I) and Y (II) sites give rise to characteristic red/pink or green luminescence, indicating a ligand-sensitized metal-centered emission. The Nd (Ib) compound shows interesting UV and blue emission through an up-conversion process.