The late transition metal complexes, are generally considered to be good tolerant toward polar media and thus are used as catalysts for polar monomer polymerizations [1, 2]. The aim of the present work is the modified synthesis and the improved understanding of the structural information of bis(4-amino-3-penten-2-onato)nickel(II), Ni (APO)2, by means of density functional theory (DFT) studies and NBO analysis. The calculated geometrical parameters were compared with those observed experimentally. In this work, the molecular equilibrium geometry, harmonic force field, and geometrical parameters of Ni(APO)2 were computed with the GAUSSIAN 03W software system [3] and NBO 5.0 [4] programs. The geometry optimization and vibrational frequencies are performed at the B3LYP6-311G* / level. The results show the trans isomer is more stable in the gas phase (E=Ecis-ETrans=27.45 kJ.mol-1). In solution the stability of trans is lowered (E=13.07 kJ.mol-1) and in the solid phase, according to x-ray report[5], the cis isomer is more stable than the trans one. The charge distribution calculated by NBO, confirms existing of significant resonance in the trans isomer relative to the cisarrangement in the gas phase. However, for Cu(APO)2 [6], according to the theoretical DFT calculations and the crystallographic results, in all arrangements, the complex has only trans configuration.

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