Novel ligands and complexes in situ generated from the copper-mediated conversions of 2,5-bis(2-hydroxyphenyl)-1,3,4-oxadiazole: Structures and magnetic properties

A novel 2-D mixed valence complex [Cu^ICu^II(L2)] _n (1; L2 = 3,5-bis(2-hydroxyphenyl)-1,2,4-triazolate) with 1-D single-stranded helical chains has been obtained from the hydrothermal reaction of Cu(Ac)₂, aqueous ammonia, and 2,5-bis(2-hydroxyphenyl)-1,3,4- oxadiazole (L1). It is remarkable that, up to now, the novel in situ copper-mediated ring-to-ring conversion reaction of L1 into L2 has not been observed before. Complex [Cu^II₂(L3)(H₂O) ₃]_n [2; L3 = N,N′-bis(α-amine-2-hydroxyphenyl) -ketazine] has been successfully isolated via reducing the concentration of L1 in comparison with the synthetic procedure of 1. The bridge ligand L3 is in situ generated through unprecedented ammonolysis of L1, which provides rare insight into the transformation of L1 to L2. The possible formation mechanism of these complexes is proposed, and the strong antiferromagnetic exchanges between Cu^II ions in 1-2 are investigated.