Thermostable 1D Lanthanide 4‐Phenylbenzoate Polymers [Ln(4‐phbz) 3 ] n (Ln = Sm, Eu, Gd, Tb, Dy, Ho) with Isolated Metal Chains: Synthesis, Structure, Luminescence, and Magnetic Properties

New 1D polymers, with the general formula [Ln(4‐phbz) 3 ] n , where Ln = Sm, Eu, Gd, Tb, Dy, Ho, and 4‐phbz is the 4‐phenylbenzoate anion, were synthesized by the reaction of Ln(NO 3 ) 3 · x H 2 O, 4‐phenylbenzoic acid, and dry KOH. Thermal analysis shows that [Eu(4‐phbz) 3 ] n is thermally stable under an inert gas up to 350 °C, and it melts at 297 °C. It is shown that the 4‐phenylbenzoate anion [ E (T 1 ) ≈ 22500 cm –1 ] in [Ln(4‐phbz) 3 ] n can play the role of an antenna and sensitize the luminescence of Eu 3+ and Tb 3+ ions. Analysis of the magnetic data of the [Gd(4‐phbz) 3 ] n complex reveals weak antiferromagnetic coupling between Gd 3+ ions ( J = –0.053 cm –1 ). The [Dy(4‐phbz) 3 ] n compound shows noticeable frequency‐dependent χ′′ signals, indicating slow magnetic relaxation and single‐molecule magnet behavior, with an energy barrier of Δ E eff / k B = 5 K.