High-Nuclearity Chiral 3 d-4 f Heterometallic Clusters Ln₆Cu₂₄ and Ln₆Cu₁₂

Based on the anion template and chiral ligand inducting role, two series of high-nuclearity 3 d-4 f heterometallic clusters with formulas [NO₃@Ln₆Cu₂₄(μ₃-OH)₃₀(μ₂-OH)₃(OAc)₆( R/ S-L)₁₂(H₂O)₂₄](NO₃)₁₄· x(H₂O) (Ln = Dy, x = 30 for 1a( R-L) and 1b( S-L); Ln = Tb, x = 40 for 2a( R-L) and 2b( S-L)) and (Et₃NH)₄[Ln₆Cu₁₂(μ₃-OH)₁₄(μ₂-Cl)₆Cl₁₂( R/ S-L)₁₂]Cl₂· x(H₂O) (Ln = Dy, x = 28 for 3a( R-L) and 3b( S-L); Ln = Tb, x = 33 for 4a ( R-L) and 4b( S-L); HL = ( R/ S)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid), have been synthesized and characterized. Structural analysis reveals that the metal skeleton of compounds 1 and 2 display a Ln₆Cu₁₂ octahedral inner core encapsulated by six outer Cu₂ units. In the Ln₆Cu₁₂ octahedron, 6 Ln³⁺ ions located at the six vertices and 12 inner Cu²⁺ ions located at the 12 edges of octahedron, and one NO₃^- locates in the center of the octahedron. The metal core of compounds 3 and 4 can be viewed as a Ln₆ octahedron encapsulated by six Cu₂ units. It is interesting that the different inorganic anions involved in the reaction result in the difference in the structures of 1 to 2 and 3 to 4. Circular dichroism spectra of 1-4 display obvious mirror symmetry effect at 600-800 nm of d-d transition of Cu²⁺, suggesting that the chirality transferred from chiral R- and S-ligand to Cu²⁺ ions in this system. Notably, the CD peak at the Cu²⁺ d-d transition position of Ln₆Cu₁₂ cluster is obviously blue-shifted compared with that of Ln₆Cu₂₄ due to the different coordinated environments of Cu²⁺. Magnetic studies indicate that 1a and 2a show weak ferromagnetic interactions, while 3a and 4a display antiferromagnetic interactions.