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 M^II-Ln^III complexes (M^II = Ni^II and Ln^III = Gd, Tb, Ho, Er, and Y; M^II = Zn^II and Ln^III = Ho^III and Er^III) of formula [M­(μ-L)­(μ-OAc)­Ln­(NO₃)₂], one nitrate-diphenoxo triply bridged Ni^II–Tb^III complex, [Ni­(μ-L)­(μ-NO₃)­Tb­(NO₃)₂]·2CH₃OH, and two diphenoxo doubly bridged Ni^II-Ln^III complexes (Ln^III = Eu, Gd) of formula [Ni­(H₂O)­(μ-L)­Ln­(NO₃)₃]·2CH₃OH have been prepared in one pot reaction from the compartmental ligand <i>N</i>,<i>N</i>′,<i>N</i>″-trimethyl-<i>N</i>,<i>N</i>″-bis­(2-hydroxy-3-methoxy-5-methylbenzyl)­diethylenetriamine (H₂L). Moreover, Ni^II-Ln^III 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 Ni^II-Ln^III complexes exhibit ferromagnetic interactions between Ni^II and Ln^III ions and, in the case of the Gd^III complexes, the <i>J</i>_NiGd 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 Ni^IIGd^III complexes and model compounds support these magneto-structural correlations as well as the experimental <i>J</i>_NiGd 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 Ni^IIDy^III complexes exhibit slow relaxation of the magnetization with Δ/<i>k</i>_B 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