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

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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 LH, N,N-bis(benzimidazol-2-ylmethyl)amine. These complexes consist of a mononuclear compound with a tridentate ligand (LH 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 [CuLH(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.

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