Potentiometric and spectrophotometric titration of Cu2+ complexes with N-isopropyl-2-methyl-1,2-propanediamine

The complexation of Cu²⁺ by N-isopropyl-2-methyl-1,2-propanediamine (L) has been studied by potentiometric and spectrophotometric titration. The dominant complexes formed in this system are [CuL]²⁺, [CuL₂]²⁺, [Cu₂L₂(OH)₂]²⁺, and [CuL(OH)₂]. The data were thoroughly tested for different models with [CuL(OH)]⁺, [CuL(OH)]⁺, [Cu(OH)]⁺, and [Cu₂(OH)₂]²⁺ as additional species. The importance of steric factors is indicated by the d-d* spectra: for [CuL₂]²⁺, (λ_max = 499 nm) the absorption maximum is shifted by 50 nm to high energies relative to [Cu(en)₂]²⁺, (λ_max = 549 nm), whereas the opposite is true for the 1:1 complexes ([CuL]²⁺ : λ_max = 712 nm,s [Cu(en)]²⁺ : λ_max = 660 nm).