MOLECULAR STRUCTURE AND CONFORMATION OF NOVEL TETRADENTATE OPEN-CHAIN OXIME LIGANDS

I.O.Fritsky¹, V.A.Kalibabchuk², E.V.Prisyazhnaya¹, T.Sliva¹, T.Glowiak³, H.Kozlowski³

¹Department of Chemistry, Shevchenko University, Kiev 252033, Ukraine
²Department of General Chemistry, National Medical University, Kiev 252004, Ukraine
³Faculty of Chemistry, University of Wroclaw, 50-383 Wroclaw, Poland

Three new open chain oxime-and-amide ligands, derivatives of alifatic diamines and 2-hydroxyiminopropanic acid: N,N'-bis(2-hydroxyimino-propionyl)-1,2-diaminoethane (1, n = 2); -1,3-diamino-propane (2, n = 3) and 1,4-diaminobuthane (3, n = 4) appeared to be a very efficient chelating agent for the Ni²⁺ and Cu²⁺ ions exhibiting both open-chain and pseudomacrocyclic co-ordination modes in the complexes [1]. As the number of the methylene groups and conformational behaviour of the ligands can impact critically on the donor ability, we have studied their crystal and molecular stucture.

In 1-3 the oxime groups are in trans-position in respect to the amide carbonyl, the amide bonds indicate trans-configuration. The molecule 1 (Fig.1) is centrosymmetric and consists of two planar parallel fragments linked by the C(4)-C(4a) bond that lies nearly perpendicular to the fragments (the torsion angle C(3)N(2)C(4)C(4a) = 85.4(2)^o) thus forming the „double desk" conformation. The molecule 2 (Fig.2) indicates elongated conformation and consists of two nearly planar fragments CH₃-C(=NOH)-C(O)NH-CH₂- linked by the methylene group. The conformationally flexible fragment -(CH₂)₃- lies nearly in the plane of the amide group O(2)C(3)N(2)C(4) (the torsion angles C(3)N(2)C(4)C(5) = -176.2(2)^o and N(2)C(4)C(5)C(4') = -171.9(2)^o). The molecule 3 (Fig.3) possesses a planar „zig-zag"-like conformation with the torsion angles deviating no more than 8^o from the values of 0^o or 180⁰. The CH₃-C(=NOH)-C(O)NH- fragments in 3 are slightly deviated from planarity because of turnover of the oxime and amide groups along C(2)-C(3) and C(2')-C(3') bonds (the dihedral angles are 4.6 and 6.7^o, respectively). The conformation of both 1 and 3 is different from that of 2 exhibiting rather folded conformation with the dihedral angle between the planes of the fragments = 96.2^o.

1. A.M. Duda , A. Karaczyn , H. Kozlowski, I.O. Fritsky, T. Glowiak , E.V. Prisyazhnaya, T.Yu. Sliva, J. Swiatek-Kozlowska, J.Chem.Soc., Dalton Trans., 1997, 3853.

Fig.1	Fig.2	Fig.3