Synthesis and properties of five unexpected copper complexes with ring-cleavage of 3,6-di-2-pyridyl-1,2,4,5–tetrazine by one pot in situhydrothermal reaction

Abstract

Solvothermal reactions of CuSO₄·6H₂O and Cu(Ac)₂·H₂O with 3,6-di-2-pyridyl-1,2,4,5-tetrazine (DPTZ) in the presence of different acetonitrile/water ratios (from 1 : 3 to 3 : 1) and temperatures (from 40 to 120 °C) successfully produce five coordination polymers: [Cu₄(SO₄)₂(H₂O)₅(L²)₂] (1), [Cu₂SO₄(H₂O)₃(L²)] (2), [Cu₂(μ-CN)₂(L¹)] (3), [Cu₂(bdc_0.5)₂(L²)(H₂O)] (4, H₂bdc = p-phthalic acid) and [Cu(L³)₂] (5) (the known mononuclear compound). Unexpectedly three ligands: 2,5-bis(2-pyridyl)-1,3,4-oxodiazole (L¹), N-bis-(R-hydroxyl-2-pyridyl)ketazine (H₂L²) and pyridine-2-carboxylate (HL³), were obtained through NN bond cleavage of DPTZ. Complexes 1, 2 and 3 own one-dimensional (1D) structures, complex 4 shows a two-dimensional (2D) framework. The new compounds were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. We focus our study on the ring-opening reaction mechanism, the occurrence process of Cu^II → Cu^I, the C–CN cleavage reaction of acetonitrile under lower temperatures (40–60 °C) and the influence of temperature and the ratio of solvent. In addition, magnetic susceptibility measurements indicate that 1, 2 and 4 show strong antiferromagnetic interactions between the adjacent Cu^II ions.