Highly pH-dependent synthesis of two novel three-dimensional dysprosium complexes with interesting magnetic and luminescence properties

Abstract

Two novel Dy-based MOFs, namely, {[Dy₂(PA)₃(H₂O)₃(DMF)]·(DMF)₂·(H₂O)}_n (1) and [Dy₂(PA)₃(H₂O)₂(DMF)₂]·(DMF)₃·(H₂O)}_n (2) (H₂PA = pamoic acid), were solvothermally synthesized from the reaction of Dy(NO₃)₃ and H₂PA at different pH values. Interestingly, both complexes can be obtained simultaneously within the pH range of 5.0–6.2, while higher pH values (6.2–7.0) promote the formation of compound 1 and lower pH values (2.0–5.0) tend to produce pure complex 2. Single-crystal X-ray diffraction studies indicate that 1 and 2 are both three-dimensional frameworks composed of dinuclear Dy(III) subunits featuring pcu networks with the point symbol of {4¹²·6³}. Significantly, their slight structure difference results in these two compounds showing completely different magnetic properties. Variable temperature magnetization measurements (χ_MT–T) demonstrate ferromagnetic interactions in compound 1, while possible antiferromagnetic interactions were observed in compound 2. Alternating current (ac) susceptibility measurements indicate that both the in-phase (χ′) and out-of-phase (χ′′) components showed frequency dependence in compound 1, suggesting that there is a slow relaxation behavior of the magnetization, which is typical of single-molecule magnets (SMMs), while no out-of-phase ac signal was noticed for 2. Furthermore, both 1 and 2 exhibit the characteristic luminescence of Dy³⁺ upon excitation at 365 nm, but with different intensities. The reasons for such magnetic and luminescence differences are discussed in detail.