Pentanuclear Spirocyclic Ni4Ln Derivatives: Field Induced Slow Magnetic Relaxation in the Dysprosium and Erbium Analogues

Five pentanuclear heterometallic isostructural complexes, [Ni<inf>4</inf>Ln(L)<inf>2</inf>(LH)<inf>2</inf>(CH<inf>3</inf>CN)<inf>3</inf>Cl]·xH<inf>2</inf>O·yCH<inf>3</inf>OH {Ln = Y^III (1), Gd^III (2), Tb^III (3), Dy^III (4) and Er^III (5)} [for 1 and 2, x = 2, y = 1; for 3, x = 6, y = 2; for 4, x = 5, y = 1; for 5, x = 2, y = 2] were prepared by the reaction of (E)-2-(hydroxymethyl)-6-{[(2-hydroxyphenyl)imino]methyl}-4-methylphenol (LH<inf>3</inf>) with LnCl<inf>3</inf>·6H<inf>2</inf>O and Ni(OAc)<inf>2</inf>·4H<inf>2</inf>O in the presence of tetrabutylammonium hydroxide (TBA-OH) base. The structural characterization reveals that compounds 1–5 contain a spirocyclic pentanuclear core [Ni<inf>4</inf>Ln(µ<inf>3</inf>-O)<inf>4</inf>(µ<inf>2</inf>-O)<inf>4</inf>]³⁺ where two triangular motifs [Ni<inf>2</inf>Ln(µ<inf>3</inf>-O)<inf>2</inf>(µ<inf>2</inf>-O)<inf>2</inf>]³⁺ are fused together through a common vertex of the Ln^III ion. The central Ln^III ion forms an eight-coordinated distorted triangular dodecahedron geometry, while the nickel(II) ions form a distorted octahedron geometry. Comprehensive dc magnetic studies reveal that antiferromagnetic exchange interaction exists between the Ni^II centres. The ac susceptibility measurement revels that dysprosium and erbium analogue shows field induced slow magnetic relaxation with an anisotropic barrier (U<inf>eff</inf>) of 25.12 cm^–1 and 22.13 cm^–1 respectively.