Construction of Cu(II)–Gd(III) metal–organic framework by the introduction of a small amino acid molecule: hydrothermal synthesis, structure, thermostability, and magnetic studies

Abstract

A new member of 3d-4f metal–organic framework (MOF), Gd₂Cu(μ-H₂O)₂(ip)₄(CH₃CH(NH₃)CO₂)₂·H₂O (1, ip = 1,3-benzene dicarboxylate), was generated by the hydrothermal self-assembly of Gd₂O₃, CuCl₂, H₂ip, and L-alanine. In 1, the slightly distorted CuO₄ squares combine with GdO₉ polyhedra via ip and CH₃CH(NH₃)CO₂ carboxyl groups to create the Gd₂Cu(CO₂)₈(CH₃CH(NH₃)CO₂)₂ rod-like substructure; such species are further linked together by phenyl units of ip to give the pcu-type rod packing. The subsequent topology analysis based on O'Keeffe's definition and classification of rod-based MOFs suggests the irl net of 1. Moreover, as evidenced by TG and XRD research, the potential microporous structure that owns the solvent-accessible volume of 246 ų, equal to 5.7% of the cell volume, can be maintained until 285 °C after the loss of coordinated water molecules. The magnetic measurements suggest weak ferromagnetic interactions within the Gd₂Cu(CO₂)₈(CH₃CH(NH₃)CO₂)₂ rod-like substructure, which is estimated by the fitting of χ_M = C/(T-θ) with θ = +0.2K and a simplified Gd–J–Cu–J–Gd mode with J = +0.23 cm⁻¹, g = 2.0, TIP = 100 × 10⁻⁶ cm³ mol⁻¹K.