Heterometallic Pentanuclear [Ni 4 Ln] (Ln III = Gd, Tb, Dy, Ho) Complexes: Accidental Orthogonality Leading to Ferromagnetic Interactions

The reaction of 6‐formyl‐2‐(hydroxymethyl)‐4‐methylphenol (LH 2 ) with Ni II and Ln III salts afforded a series of heterometallic pentanuclear compounds [Ni 4 Ln(L) 4 (OAc) 2 (MeOH) 4 ](NO 3 )(MeOH) [Ln III = Gd ( 1 ), Dy ( 2 ), Tb ( 3 ), Ho ( 4 )]. Four dianionic L 2– ligands and two acetate anions hold together four Ni II and one Ln III ion to form a Ni 4 Ln core possessing a distorted tetrahedral geometry. All the Ni II ions are hexacoordinate (6 O) with a distorted octahedral geometry whereas the Ln III ion is octacoordinate (8 O) with a distorted square‐antiprism geometry. All the Ni II ions are connected to the central Ln III ion through μ 2 bridging of one deprotonated phenolic oxygen and two deprotonated alkoxy oxygen atoms. The magnetic properties of 1 – 4 were investigated in the temperature range 2–300 K. The magnetic properties of 1 were fitted by using a Hamiltonian containing isotropic exchange, Ni II local zero‐field‐splitting, and Zeeman effects ( Ĥ = Ĥ exchange + Ĥ zfs + Ĥ zeeman ). The molecular structures of 1 – 4 reveal that the Ni–O–Ln angle is around 89° whereas the Ni–O–Ni angle is about 96°. Because of this accidental orthogonality, ferromagnetic interactions between the nearest‐neighbor Ni II ions and between Ni II and Ln III ions have been observed. The observed J values are 0.34 and 1.88 cm –1 between Gd III –Ni II and Ni II –Ni II , respectively.