Self-assembly of high-nuclearity copper cages: Tricorne Cu₂₁ and saddlelike cyclic Cu₁₆

Reaction of cupric salts with H₂Rppz (R = H, Me; H ₂ppz = 3-(2-hydroxyphenyl)pyrazole; H₂Meppz = 3-(2-hydroxy-5-methylphenyl)pyrazole) in the presence of sodium azide and triethylamine as bases gave two high-nuclearity copper cage compounds [HNEt ₃]₂·[Cu₂₁(CH₃CN) ₂(H₂O)(μ₂-N₃)₆- (μ₃-N₃)₂(ppz)₁₈]·(H ₂O)₃·(EtOH)₂ (1) and [Cu ₁₆(EtOH)₂(H₂O)₂-(Meppz) ₁₆]·9.5 H₂O (2), respectively. X-ray crystallographic studies revealed that molecular skeletons of 1 and 2 are unique tricorne Cu₂₁ and saddlelike cyclic Cu₁₆ aggregates, respectively. The magnetic properties studies showed overall antiferromagnetic interactions in 1 and 2. Quantum Monte Carlo simulations by using a 3-J model for 1 and a 2-J model for 2 were performed, which indicated that the magnetic couplings within the triangular copper units in 1 are ferromagnetic and those between other copper ions are antiferromagnetic, whereas in 2 all magnetic couplings between adjacent copper ions are exclusively antiferromagnetic.