0022-4766/05/4605-0813 © 2005 Springer Science+Business Media, Inc. 813 Journal of Structural Chemistry, Vol. 46, No. 5, pp. 813-823, 2005 Original Russian Text Copyright © 2005 by G. V. Girichev, N. I. Giricheva, N. P. Kuzmina, Yu. S. Levina, and A. Yu. Rogachev MOLECULAR STRUCTURE OF NiO 2 N 2 C 16 H 14 FROM GAS-PHASE ELECTRON DIFFRACTION AND QUANTUM CHEMICAL DATA G. V. Girichev, 1 N. I. Giricheva, 2 N. P. Kuzmina, 3 Yu. S. Levina, 3 and A. Yu. Rogachev 3 UDC 539.27 Gas-phase electron diffractometry was used to study the molecular structure of N,N -ethylene- bis(salicylaldiminato)nickel(II), NiO 2 N 2 C 16 H 14 , [hereinafter Ni(salen)] at 583(5) K. The molecule has 2 symmetry with a practically planar structure of the NiN 2 O 2 coordination unit and with internuclear distances r (Ni–O) = 1.882(21) Å and r (Ni–N) = 1.889(22) Å. The results of B3LYP/CEP-31G molecular structure calculations are in good agreement with experimental data, whereas the RHF/ -31G method significantly overestimates the Ni–N internuclear distance and gives worse results for other structural parameters. According to 3LYP/CEP-31G calculations, the 1 A low-spin state is 28 kJ/mole lower in energy than the 3 high-spin state. Keywords: Ni(salen), NiO 2 N 2 C 16 H 14 , molecular structure, geometrical parameters, gas-phase electron diffraction, quantum chemistry. Schiff bases are widely used as ligands for syntheses of coordination compounds [1]. Due to possible combinations of various functional groups in their molecules, one can obtain coordination compounds with various metals, varying the functional properties of these compounds within wide limits. Tetradentate Schiff donor bases [N 2 O 2 ] are most often used to synthesize 3d transition metal complexes. The properties of these complexes depend on the electronic nature and conformational characteristics of the ligand [1]. Cu(II) and Ni(II) complexes with Schiff bases and diamine, -diketone or salicylic aldehyde derivatives have been studied most thoroughly. Due to their plane-square structure and the presence of an [N 2 O 2 ] donor center, these complexes are involved in various intermolecular interactions and in reactions that form supramolecular structures. In the last decade, there has been a revival of interest in these compounds because of their use in syntheses of f–d type heterobimetallic complexes [X 3 Ln(SB)M] (Ln is a REE(III) ion, – is an anion ligand, and M(SB) are Cu(II) or Ni(II) complexes with Schiff bases and diamine, -diketone, or salicylic aldehyde derivatives) with potential magnetic properties [2-4] and volatility [5-8]. In these heteronuclear compounds, the M(SB) complex plays the role of a neutral ligand that enters in the coordination sphere of the central REE ion and coordinates two oxygen atoms. The electronic and spatial structure of M(SB) complexes certainly affects the formation, structure, and properties of heterometal complexes of [X 3 Ln(SB)M] type; therefore, a detailed study of M(SB) complexes is of great interest. N,N -ethylene-bis(salicylaldiminato)nickel(II), Ni(salen), is one of these “ligand” complexes [9]. The Ni(salen) complex was investigated by X-ray diffraction (XRD) analysis [10-12]. In Ni(salen) molecules, the central nickel atom has a plane-square environment and coordinates two nitrogen atoms and two oxygen atoms of the ligand. The crystal structure of 1 Ivanovo State Chemical Engineering University; girichev@isuct.ru. 2 Ivanovo State University. 3 M. V. Lomonosov Moscow State University, Chemical Faculty. Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 5, pp. 843-853, September-October, 2005. Original article submitted January 12, 2005.