Single-Strand Molecular Wheels and Coordination Polymers in Copper(II) Benzoate Chemistry by the Employment of α-Benzoin Oxime and Azides: Synthesis, Structures, and Magnetic Characterization.

The use of α-benzoin oxime (bzoxH₂) in copper(II) benzoate chemistry, in the absence or presence of ancillary azido ligands, is reported. The reaction of Cu(O₂CPh)₂ ·2H₂O with one equivalent of bzoxH₂ in N, N-dimethylformamide (DMF) affords the decanuclear complex [Cu₁₀(bzox)₁₀(DMF)₄] ( 1) in good yield. Dissolution of 1 in CH₂Cl₂ leads to the subsequent isolation of the solvent-free complex [Cu₁₀(bzox)₁₀] ( 2) in moderate yields. Complexes 1 and 2 are isostructural and possess a loop or single-strand molecular wheel topology. The bzox^2- dianions behave as η¹:η¹:η²:μ₃ ligands, which give rise to an overall [Cu₁₀(μ-ONR)₁₀(μ-OR′)₁₀] core. Both 1 and 2 stack to form nanotubular columns with beautiful supramolecular architectures. The reaction of Cu(O₂CPh)₂ ·2H₂O with bzoxH₂ and NaN₃ in a 1:1:1 molar ratio in MeOH gives the bzoxH₂-free complex [Cu(N₃)(O₂CPh)(MeOH)] _n ( 3), which is a 1D chain. The Cu^II atoms in 3 are linked by a single, end-on N₃^- group, a syn, syn-η¹:η¹:μ PhCO₂^- ion, and an oxygen atom from the bridging MeOH ligand. The 1D chains are hydrogen bonded into 2D sheets through N_azide ···H(O_MeOH) interactions. Variable-temperature, solid-state direct-current magnetic studies were carried out on 1- 3. The data for 1 and 2 indicate very strong antiferromagnetic exchange interactions and a S = 0 ground state, which is expected for even-membered loop arrays of Cu^II atoms. In contrast, 3 exhibits ferromagnetic exchange interactions; the data were fitted to the appropriate equation derived from the Hamiltonian H = - JΣ( S_i · S_i+1), which includes a zJ′ interchain interaction term. The best-fit parameters were J = +49.6(4) cm^-1, g = 2.067(3), and zJ′ = 2.3(1) K. The combined results demonstrate the ligating flexibility of both the bzoxH₂ and azido groups and their usefulness in the synthesis of polynuclear Cu^II clusters and coordination polymers. [ABSTRACT FROM AUTHOR]