Three analogous lanthanide-containing complexes were isolated, with the molecular formula Ln 4 (μ 3 -OH) 2 (tmhd) 4 L 6 ·2CH 3 CN (where Ln = Eu( 1 ), Gd( 2 ) and Dy( 3 ); HL = 5-phenyl-8-hydroxylquinoline; and Htmhd = 2,2,6,6-tetramethyl-3,5-heptanedione). Single-crystal X-ray diffraction measurements performed on 1–3 revealed that they were all composed of Ln 4 (μ 3 -OH) 2 centers with butterfly-shaped arrangements. Investigations into the luminescence properties and lifetime of 1 showed characteristic emission peaks of the Eu 3+ ion and an average luminescence lifetime of 9.26 μs. Detailed magnetic studies suggested that antiferromagnetic interactions existed in 2 and 3 , and that there was a remarkable magnetocaloric effect with a −Δ S m value of 17.94 J K −1 kg −1 for 2 , and a slow magnetic relaxation process with an energy barrier Δ E / k B of 35.8 K for 3 .