Syntheses and properties of two pH-directed types of cobalt–lanthanoid heterometallic complexes constructed from 2,5-dichlorobenzoate and 1,10-phenanthroline

Abstract

By adjusting the pH values, two types of heterometallic complexes originated from the same raw materials but with different structures and colors have been successfully designed and constructed. Eleven 3d–4f cobalt–lanthanoid heterometallic complexes, [Ln₂Co₂(2,5-DCB)₁₀(phen)₂] [Ln = Nd (1 and 1a), Sm (2 and 2a), Eu (3 and 3a), Gd (4), Tb (5), Dy (6), Er (7), and Yb (8)], were prepared through the self-assembly reactions of Ln(NO₃)₃·nH₂O, Co(NO₃)₂·6H₂O, 2,5-dichlorobenzoic acid (2,5-HDCB), NaOH, and 1,10-phenanthroline (phen) under solvothermal conditions. All of these complexes were characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Complexes 1 and 1a (2 and 2a, 3 and 3a) are available at different pH ranges, respectively. Their structures and colors are different from each other. Complexes 1–8 and 1a–3a are found to be isostructural, respectively. The photoluminescence properties of 3 and 3a as well as the magnetic properties of 1, 2, 1a, 2a, and 4–8 were investigated. Complexes 3 and 3a display similar characteristic luminescence of Eu(III) and different emission lifetimes. Complex 4 exhibits weak ferromagnetic coupling between the spin carriers below 10 K, and complex 6 shows a slow magnetic relaxation behavior.