Unusual changes in hyperfine coupling constants observed for copper(II) complexes with N,N-bis(benzimidazol-2-ylmethyl)amine and its homologues; X-ray crystal structure determinations of [CuLPri(NO3)(MeOH)]NO3, [CuLBut(NO3)(MeOH)]NO3, [CuLBun(NO3)]NO3, and [CuLBui(NO3)]NO3

Abstract

Crystal structures of four copper(II) complexes, [CuL^Pri(NO₃)(MeOH)]NO₃(5), [CuL^Bun(NO₃)]NO₃(6), [CuL^Bui(NO₃)]NO₃(7), and [CuL^But(NO₃)(MeOH)]NO₃(9) were determined by X-ray diffraction methods, where L^Bun, L^But, L^Bui, and L^Pri respresent the n-butyl, t-butyl, isobutyl, and isopropyl derivative, on the amine nitrogen atom, of L^H, N,N-bis(benzimidazol-2-ylmethyl)amine. These complexes consist of a mononuclear compound with a tridentate ligand (L^H or its derivative) and a bidentate nitrate ion. These show quite similar absorption spectra in methanol solution. However, remarkable differences were observed for |A_∥| values in e.s.r. spectra (frozen methanol solution) irrespective of the small change in the g_∥ value. Bulky substituents, such as t-butyl, on the amine nitrogen atom decrease the |A_∥| value considerably {|A_∥|= 160 × 10^–4 cm^–1 for [CuL^H(NO₃)]⁺ and |A_∥|= 110 × 10^–4 cm^–1 for [CuL^But(NO₃)(MeOH)]⁺}, suggesting that the change of orientation of the lone pair orbital of the amine nitrogen atom produces a sizeable effect on |A_∥| values in these complexes.