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

摘要

The use of α-benzoin oxime (bzoxH _2) in copper(II) benzoate chemistry, in the absence or presence of ancillary azido ligands, is reported. The reaction of Cu(O _2CPh) _2?·2H _2O with one equivalent of bzoxH _2 in N,N-dimethylformamide (DMF) affords the decanuclear complex [Cu _(10)(bzox) _(10)(DMF) _4] (1) in good yield. Dissolution of 1 in CH _2Cl _2 leads to the subsequent isolation of the solvent-free complex [Cu _(10)(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 ?· ~1:?· ~1: ?· ~2:μ _3 ligands, which give rise to an overall [Cu _(10)(μ-ONR) _(10)(μ-OR') _(10)] core. Both 1 and 2 stack to form nanotubular columns with beautiful supramolecular architectures. The reaction of Cu(O _2CPh) _2?· _2H _2O with bzoxH _2 and NaN _3 in a 1:1:1 molar ratio in MeOH gives the bzoxH 2-free complex [Cu(N 3)(O 2CPh)(MeOH)] n (3), which is a 1D chain. The Cu II atoms in 3 are linked by a single, end-on N _3 ~- group, a syn,syn-?· ~1: ?· ~1:μ PhCO _2 ~- 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 = -J?￡(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 bzoxH _2 and azido groups and their usefulness in the synthesis of polynuclear Cu ~(II) clusters and coordination polymers.