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Four co-edge rhomboid [Ln 4 (μ 3 -OH) 2 ]-based 1D chainlike LnCPs were synthesized based on orotic acid. The Gd-containing complex displays a large MCE of −Δ S m max = 37.11 J kg−1 K−1, and the Eu- and Tb-based polymers exhibit characteristic Ln(III) luminescence. [Display omitted] • Four isostructural 1D LnCPs with rhomboid [Ln 4 (μ 3 -OH) 2 ]-based chainlike structure were obtained hydrothermally. • The Gd(III)-containing polymer displays a large MCE with − Δ S m max value of 37.11 J kg−1 K−1. • The Eu- and Tb-based polymers exhibit characteristic Eu(III)/Tb(III) luminescence. Four isostructural lanthanide coordination polymers with orotic acid (H 3 OA) as building ligand, {[Ln(HOA)(μ 3 -OH)(H 2 O) 2 ]·H 2 O} n (Ln = Eu (1); Gd (2); Tb (3); Dy (4)), were synthesized under hydrothermal conditions. Single-crystal X-ray diffraction analyses demonstrate that complexes 1 – 4 have an one-dimensional (1D) chainlike structure consisting of rhomboid [Ln 4 (μ 3 -OH) 2 ] unit and HOA2- linker. Magnetic studies indicate that 2 displays a large magnetocaloric effect with magnetic entropy value of 37.11 J kg−1 K−1 at 2.0 K for Δ H = 7.0 T. This is a considerable value among the reported molecular magnetic coolants, and has a great application potential in the field of ultra-low temperature refrigeration. In addition, the solid-state photophysical properties of 1 and 3 exhibit obvious characteristic Eu(III) and Tb(III) photoluminescence emission in the visible region, suggesting that Eu- and Tb-based luminescence were sensitized effectively by the energy transfer from the ligand to the metal centers. [ABSTRACT FROM AUTHOR]

Two series of lanthanide complexes based on 4-chlorophenylacetic acid (HCPA), dinuclear [Ln 2 (CPA) 6 (DMF) 2 (H 2 O) 2 ] (Ln = Eu (1); Gd (2); Tb (3); Dy (4)) and one-dimensional (1D) linear [Ln 2 (CPA) 6 (H 2 O)] n (Ln = Eu (5); Gd (6); Tb (7); Dy (8)), were prepared, which are sensitive to the pH value. The dinuclear structure can be obtained when the pH value was controlled to be about 4.2, while the 1D structure can be formed when the pH value is ca. 5.1. The structure transformation of the dinuclear to 1D analogue at different pH values indicates that the CPA− ligand has a better affinity to replace the H 2 O/DMF molecule to bridge the neighboring Ln3+ ions to form the 1D structure at a higher pH value (∼5.1). The magnetic studies show that complexes 2 and 6 with isotropic Gd3+ ion display significant cryogenic magnetocaloric effect with a maximum −ΔS m value of 20.27 J kg−1 K−1 at 3 K and 7 T and 22.50 J kg−1 K−1 at 2 K and 7 T, respectively. Furthermore, the solid-state photophysical properties of 1 / 5 and 3 / 7 were studied and respectively exhibit strong characteristic emission peaks of Eu3+ and Tb3+ ions in the visible region, indicating that Eu- and Tb-based luminescences are sensitized effectively by the energy transfe from the ligand to the spin centers. Two series of dinuclear and 1D lanthanide complexes have been successfully prepared with HCPA, and are sensitive to pH value. The Gd-containing complexes display significant MCE, and the Eu- and Tb-based polymers exhibit strong characteristic lanthanide luminescence. Image 1 • Two series of lanthanide complexes were obtained solvothermally. • The dinuclear or 1D complexes are sensitive to the pH value. • The Gd-based complexes display significant MCE. • The Eu- and Tb-based complexes display characteristic Eu3+/Tb3+ luminescence. [ABSTRACT FROM AUTHOR]