Lanthanide Contraction in Action: Structural Variations in 13 Lanthanide(III) Thiophene-2,5-dicarboxylate Coordination Polymers (Ln = La–Lu, Except Pm and Tm) Featuring Magnetocaloric Effect, Slow Magnetic Relaxation, and Luminescence-Lifetime-based Thermometry

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Thirteen new three-dimensional lanthanide(III)-2,5-thiophenedicarboxylate coordination polymers (Ln-CPs) with general formulas of [Ln 2 (2,5-TDA) 3 (DMA) 2 (H 2 O)] n (Ln-CPs 1 – 4 ) and [Ln 2 (2,5-TDA) 3 (DMA) 2 ] n (Ln-CPs 5 – 13 ) (where 2,5-TDA 2– = 2,5-thiophedicarboxylate dianion, DMA = N, N ′-dimethylacetamide, and Ln = La ( 1 ), Ce ( 2 ), Pr ( 3 ), Nd ( 4 ), Sm ( 5 ), Eu ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 ), Ho ( 10 ), Er ( 11 ), Yb ( 12 ) Lu ( 13 )) have been synthesized solvothermally under two different temperature conditions in a DMA–H 2 O mixed solvent system. A structural analysis discloses that the four Ln-CPs 1 – 4 crystallize in the orthorhombic space group Pna 2 1, whereas the eight Ln-CPs 5 – 8 and 10 – 13 crystallize in the triclinic P ̅1 space group and Ln-CP 9 (Dy) adopts the monoclinic P 2/ c space group. The distinct crystal structures and coordination features indicate that lanthanide contraction, ancillary DMA molecules, and different coordination modes identified for 2,5-TDA 2– play deciding roles in the self-assembly of Ln-CPs 1 – 13 . The Ln(III) centers in compounds 1 – 13 exhibit three different coordination numbers, 9 (only 1; around La1), 8 ( 1 – 8 and 10 – 12 ), and 7 ( 4, 8, 9 and 11 – 13 ) with monocapped-square-antiprismatic, bicapped-trigonal-prismatic, and monocapped-trigonal-prismatic geometries, respectively. The title compounds display distinct 3D coordination frameworks with dinuclear (La 2 O 15; for 1 and Ln 2 O 14; for 2 – 4 ) SBUs and tetranuclear [Ln 4 O 28 ] SBUs (for compounds 5 – 13 ). Variable-temperature magnetic susceptibility measurements were investigated for Ln-CPs 7 – 11 with an applied dc field of 1 kOe. The weak antiferromagnetic interaction and small ligand/metal mass ratio make Ln-CP 7 (Gd) a good candidate for low-temperature magnetic refrigeration with an impressive −Δ S m max = 31.0 J kg –1 K –1 (63.6 mJ cm –3 K –1 ) at T = 2 K and Δ H = 7 T. Furthermore, the frequency and temperature dependences of the alternating current (ac) susceptibilities have been studied to explore the magnetic dynamics of Ln-CPs 8 – 10 . Importantly, for compound 9 (Dy), the χ′ m and χ″ m curves and Cole–Cole plots at 2–6 K suggest the existence of slow magnetic relaxation behavior. Luminescence thermometry studies have been performed at 298–373 K for Ln-CPs 6 and 8 . The Eu analogue ( 6 ) features a weak temperature dependence of luminescence lifetime (relative sensitivities of 0.43% K –1 and 0.34% K –1 at 298 and 373 K, respectively), whereas the Tb analogue ( 8 ) is a good lifetime-based luminescent thermometer with a constant relative sensitivity value of 1.35% K –1 in the investigated temperature range.