Steric Control of Electronic Effects in Diacetylated Nickel(II) Schiff Base Complexes

X-ray structural analysis, electrochemistry,¹³C NMR spectroscopy, and infrared spectroscopy of the diacetylated Schiff base complexes [Ni(Me₂Ac₂H₂malen)] and [Ni(Me₂Ac₂Me₂malen)] are reported. Differences in the number of methyl groups on the chelate backbone (two for [Ni(Me₂Ac₂H₂malen)], four for [Ni(Me₂Ac₂Me₂malen)]) cause the acetyl groups to be rotated out of the NiN₂0₂plane by 16.8 and 58.2°, respectively. Electrochemical measurements on the diacetylated and analogous deacetylated complexes show that delocalization effects from the acetyl groups have been decreased by the rotating of the acetyl groups out of the chelate plane. This interpretation is supported by¹³C NMR and infrared spectroscopic measurements. As such, the use of steric effects to regulate electronic effects has been demonstrated. [Ni(Me₂Ac₂H₂malen)] crystallized in the monoclinic system (P2₁/c) with unit cell dimensions a = 14.686 (2) Å, b~ 17,734 (3) Å, c = 11.412(1) Å, β = 101.16 (1)°, and Z = 8; R = 0.049 and R_w= 0.054 for 2730 observed reflections. [Ni(Me₂Ac₂Me₂malen)] crystallized in the monoclinic system (C2/c) with unit cell dimensions a = 7.689 (2) Å, b = 8.686 (2) Å, c = 25.579 (9) Å, β = 103.84 (3)°, and Z = 4; R = 0.042 and Rw = 0.042 for 1370 observed reflections.