Dual Shell-like Magnetic Clusters Containing Ni^II and Ln^III (Ln = La, Pr, and Nd) Ions

Dual shell-like nanoscopic magnetic clusters featuring a polynuclear nickel(II) framework encapsulating that of lanthanide ions (Ln = La, Pr, and Nd) were synthesized using Ni(NO₃)₂·6H₂O, Ln(NO₃)₃·6H₂O, and iminodiacetic acid (IDA) under hydrothermal conditions. Structurally established by crystallographic studies, these clusters are [La₂₀Ni₃₀(IDA)₃₀(CO₃)₆(NO₃)₆(OH)₃₀(H₂O)₁₂](CO₃)₆·72H₂O (1), [Ln₂₀Ni₂₁(C₄H₅NO₄)₂₁(OH)₂₄(C₂H₂O₃)₆(C₂O₄)₃(NO₃)₉(H₂O)₁₂](NO₃)₉·nH₂O [C₂H₂O₃ is the alkoxide form of glycolate; Ln = Pr (2), n = 42; Nd (3), n = 50], and {[La₄Ni₅Na(IDA)₅(CO₃)(NO₃)₄(OH)₅(H₂O)₅][CO₃]·10H₂O}_∞ (4). Carbonate, oxalate, and glycolate are products of hydrothermal decomposition of IDA. Compositions of these compounds were confirmed by satisfactory elemental analyses. It has been found that the cluster structure is dependent on the identity of the lanthanide ion as well as the starting Ln/Ni/IDA ratio. The cationic cluster of 1 features a core of the Keplerate type with an outer icosidodecahedron of Ni^II ions encaging a dodecahedral kernel of La^III. Clusters 2 and 3, distinctly different from 1, are isostructural, possessing a core of an outer shell of 21 Ni^II ions encapsulating an inner shell of 20 Ln^III ions. Complex 4 is a three-dimensional assembly of cluster building blocks connected by units of Na(NO₃)/La(NO₃)₃; the structure of the building block resembles closely that of 1, with a hydrated La^III ion internalized in the decanuclear cage being an extra feature. Magnetic studies indicated ferromagnetic interactions in 1, while overall antiferromagnetic interactions were revealed for 2 and 3. The polymeric, three-dimensional cluster network 4 displayed interesting ferrimagnetic interactions.