Family of Carboxylate- and Nitrate-diphenoxo Triply Bridged Dinuclear Ni^IILn^III Complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): Synthesis, Experimental and Theoretical Magneto-Structural Studies, and Single-Molecule Magnet Behavior

Seven acetate-diphenoxo triply bridged MII-LnIII complexes (MII = NiII and LnIII = Gd, Tb, Ho, Er, and Y; MII = ZnII and LnIII = HoIII and ErIII) of formula [M(μ-L)(μ-OAc)Ln(NO3)2], one nitrate-diphenoxo triply bridged NiII–TbIII complex, [Ni(μ-L)(μ-NO3)Tb(NO3)2]·2CH3OH, and two diphenoxo doubly bridged NiII-LnIII complexes (LnIII = Eu, Gd) of formula [Ni(H2O)(μ-L)Ln(NO3)3]·2CH3OH have been prepared in one pot reaction from the compartmental ligand N,N′,N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L). Moreover, NiII-LnIII complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(μ-L)(μ-BzO)Dy(NO3)2] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO3)2]·3CH3CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(μ-O2)Ln bridging fragment of ∼22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ∼13° and ∼2°, respectively. All NiII-LnIII complexes exhibit ferromagnetic interactions between NiII and LnIII ions and, in the case of the GdIII complexes, the JNiGd coupling increases weakly but significantly with the planarity of the M–(O)2–Gd bridging fragment and with the increase of the Ni–O–Gd angle. Density functional theory (DFT) theoretical calculations on the NiIIGdIII complexes and model compounds support these magneto-structural correlations as well as the experimental JNiGd values, which were found to be ∼1.38 and ∼2.1 cm–1 for the folded [Ni(μ-L)(μ-OAc)Gd(NO3)2] and planar [Ni(H2O)(μ-L)Gd(NO3)3]·2CH3OH complexes, respectively. The NiIIDyIII complexes exhibit slow relaxation of the magnetization with Δ/kB energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(μ-L)(μ-BzO)Dy(NO3)2] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO3)2]·3CH3CN, respectively.