Dinuclear and polymeric copper(I) ethylene adducts bridged by bis-pyridyl derivatives of 1,2,4-triazole and 1,2,4,5-tetrazine

Abstract

The reaction of [Cu(MeCN)4]PF6 with 3,5-bis(2-pyridyl)-1H-1,2,4-triazole (Hbptrz) in MeOH under C2H4 afforded the colorless needle crystals of [Cu2(bptrz)(C2H4)2]PF6·MeOH (1). The X-ray crystallographic study showed that there are two [Cu2(bptrz)(C2H4)2]+ cation moieties, two PF6− anions and two solvated MeOH molecules in the unit cell. This result indicates that the central triazole ring was deprotonated to produce the anionic bptrz ligand. Each Cu(I) atom is coordinated by two chelate N atoms of bptrz and the CC bond of C2H4 in the trigonal–planar geometry to produce a notable dinuclear Cu(I)–bptrz/C2H4 adduct bearing the anionic bptrz in the transoid conformation. In contrast, the reaction of Cu(NO3)2·H2O, Cu turnings and 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (4-bptz) in Me2CO under C2H4 gave black brick crystals of {[Cu4(4,5-H2-4-bptz)2(C2H4)2(NO3)4]·Me2CO·0.5H2O}n (2). This result indicates that 3,6-bis(4-pyridyl)-4,5-dihydro-1,2,4,5-tetrazine (4,5-H2-4-bptz) was produced by the two-electron reduction of 4-bptz. Four Cu(I) atoms are bridged by two 4,5-H2-4-bptz and four NO3− anions to form two distinct rectangular [Cu4(4,5-H2-4-bptz)2(NO3)4] frameworks. Furthermore, these rectangular [Cu4(4,5-H2-4-bptz)2(NO3)4] subunits are linked via the N atom in the central 4,5-dihydrotetrazine ring each other to generate a unique 2-D Cu(I)–4,5-H2-4-bptz/C2H4–NO3 coordination polymer with a channel structure along the a-axis. Thermogravimetric analysis (TG–DTA) showed that complexes 1 and 2 were thermochemically stable to a relatively high temperature.