STEREOCHEMICAL CHANGES BY CHELATATION:
N,N'-BUTYLENEBISSALICYLALDIMINE AND ITS COPPER COMPLEX

T. Frišcic, B. Kaitner and E. Meštrovic

Laboratory of General and Inorganic Chemistry, Faculty of Science,
University of Zagreb, Ul. kralja Zvonimira, HR-10000 Zagreb, Croatia

Keywords: symmetrically bridged Schiff base, tetradentate ligand, copper(II) salicylaldiminate

N,N'-butylenebissalicylaldimine (I) was prepared from 1,4-diaminobutane and salicylaldehide. The copper complex was prepared in a template reaction using NaOH as a deprotonation agent. The crystals of (II), obtained by slow evaporation, consist of two discrete molecules of copper complex bridged by a sodium ion.

(I)	(II)

(I) C₁₈H₂₀N₂O₂, P 2₁/c, a = 15.345(1) Å, b = 5.8799(5) Å, c = 8.9744(8) Å,
b = 90.145(8) ^o, V = 809.72(8) ų, Z = 2, D_c = 1.216 gcm^-3, l(MoKa) = 0.71073 Å,
R = 0.051 and wR = 0.089 for 1179 independent reflections with I_net >= 2s I_net.

(II) C₃₆H₃₆N₅NaCu₂O₇, P bcn, a = 16.908(5) Å, b = 11.409(4) Å, c = 18.172(5) Å,
V = 3505.4(19) ų, Z = 4, D_c = 1.517 gcm^-3, l(MoKa) = 0.71073 Å, R = 0.039 and wR = 0.058 for 1975 reflections with I_net >= 2s I_net.

The main feature of (I) is the existence of an O-H···N intramolecular chelate ring hydrogen bond. It was assumed that the length of the bridging chain in (I) could introduce certain strain in the molecule of its Cu^II complex thus influencing to the geometry of copper atom coordination sphere. The sodium ion bridges two metal complex molecules via strong Na⁺···O electrostatic attractions. The nitrate ion completes the Na⁺ surroundings to an irregular octahedron. Perhaps the presence of an alkaline metal ion partially stabilizes the strained conformation of the ligand.