Syntheses of new di-nuclear and tetra-nuclear lanthanide 9-anthracenecarboxylates: Magnetocaloric effect, slow magnetic relaxation and luminescent properties

Lanthanide complex-based materials with magnetic and luminescent properties have received a great deal of attention, owing to their importantly potential applications in diverse fields. In this work, the 9-anthracenecarboxylic acid (9-Haca) as bridging ligand was applied in combination with optically active pi-conjugated 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) to construct a series of new di-nuclear and tetra-nuclear lanthanide 9-anthracenecarboxylates [La-2(9-aca)(6)(tptz)(2)(mu-H2O)]<middle dot>0.25H(2)O (1), [Ln(2)(9-aca)(6)(tptz)(2)(H2O)(2)]<middle dot>0.5AQ<middle dot>CH(3)COOH2H(2)O [Ln = Sm (2a), Eu (2b), Gd (2c), Tb (2d), Dy (2e), Tm (2f); AQ = 9,10-anthracenedione] and [Ln(4)(9-aca)(10)(tptz)(2)(CH3COO)(2)]<middle dot>H2O [Ln = Eu (3a), Gd (3b), Dy (3c)]. 1 displays a di-nuclear centrosymmetric moiety [La-2(9-aca)(6)(tptz)(2)(mu-H2O)] built up from two complex [La(9-aca)(2)(tptz)] groups bridged by one H2O molecule and two syn-syn-mu(2)-eta(1):eta(1)-9-aca(-) bridging ligands, while 2a-2f are isostructural and comprise another di-nuclear centrosymmetric moieties [Ln(2)(9-aca)(6)(tptz)(2)(H2O)(2)] based on two complex [Ln(9-aca)(2)(tptz)(H2O)] groups connected by two syn-syn-mu(2)-eta(1):eta(1)-9-aca(-) bridging ligands. 3a-3c are isostructural and show tetra-nuclear centrosymmetric moieties [Ln(4)(9-aca)(10)(tptz)(2)(CH3COO)(2)] containing three types of coordination modes of 9-aca(-) ligands. The present compounds offer the only examples of lanthanide 9-anthracenecarboxylates decorated by optically active tptz. Magnetic investigations of 2a, 2c-2f, and 3b-3c indicate that 3c is typical of slow relaxation of the magnetization, while 2c and 3b show significant magnetocaloric effect (MCE) with the value of -Delta S-m of 5.26 J/(kg<middle dot>K) at 4 K and 15.65 J/(kg<middle dot>K) at 2 K (Delta H = 7 T), respectively. The luminescent properties were also studied and reveal that the characteristic luminescent properties of the pi-conjugated aromatic ligands are introduced into magnetic lanthanide 9-anthracenecarboxylates, simultaneously exhibiting slow magnetic relaxation (or MCE) and luminescent properties.<br /> (c) 2023 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.