Two well-isolated rare earth ion-based one-dimensional (1D) compounds with the general formulae [RE(3,5-DNBz)₃(H₂O)₂](H₂O) (RE = Y(1) and Dy(2); 3,5-DNBz = 3,5-dinitrobenzoic acid) have been assembled under hydrothermal conditions with the bulky ligand 3,5-DNBz and structurally characterized by single-crystal X-ray diffraction, IR, TG–DTA, and elemental analysis. 1 and 2 are isostructural and possess a chain structure bridged alternatively by double and quadruple carboxylic groups of the 3,5-DNBz anions. For 2, the rare earth ion center surrounded by six 3,5-DNBz anions and two water molecules is in an intermediate coordination geometry between the ideal square anti-prism (SAP) and bicapped trigonal prism (BTP). Magnetic investigation using direct-current (dc) measurement revealed weak ferromagnetic intra-chain interaction in the Dy analogue 2. In the alternating-current (ac) susceptibility measurements, 2 was revealed dominating quantum tunnelling relaxation under zero dc field, while it exhibited the coexistence of quantum tunnelling and thermal activated relaxations (with an energy barrier U_eff/k of 77.8 K) in 300 Oe dc field, and the quenching of quantum tunnelling and an almost pure thermal magnetic relaxation (U_eff/k = 90.9 K) in 2 kOe dc field.