Solvatochromism and Structure of Acetylacetonatocopper(II) Complexes with N,N′-Dipropyl-, N,N,N′,N′-Tetrapropyl-, and N,N- and N,N′-Diisopropylethylenediamines

Seven copper(II) complexes of the general formula [Cu(acac)(diam)]X were prepared, where acac and diam stand for acetylacetonate and one of the diamines in the title, and X− for a bulky univalent anion, respectively. Their solvatochromism was compared with that of the corresponding complexes with N,N,N′,N′-tetramethylethylenediamine and related diamines, to see the effect of their bulky N-alkyl groups. X-ray crystal analyses showed that the perchlorates of N,N′- and N,N-diisopropyl complexes are apparently 6- and 5-coordinated, respectively, in their crystals, although their ClO4− ions are held extremely weakly and are easily driven out by solvent molecules in solution, leading to their solvatochromism. The Cu–N and Cu–O(acac) bond distances in the former, 199.5(4)/202.4(5) and 190.6(4)/190.1(4) pm, respectively, are similar to each other, while the Cu–N(isopropyl)2 distance, 206.4(9) pm, in the latter is notably longer than the Cu–NH2 distance, 196(1) pm.