The results of DFT calculations for the complex cation [Fe(DAPP)(abpt)](2+) in the spin transition compound [Fe(DAPP)(abpt)](ClO4)(2) are presented. The experimental X-ray data at room temperature, in the high-spin (HS) state, display the disorder over two configurations in the DAPP ligand. The single point DFT calculations result in quite close HS-LS energy gaps in two conformations. The calculations with geometry optimization suggest that the presence of two conformations is not an intrinsic property of the complex cation and show that it may be a favorable factor for the spin transition. (C) 2004 Elsevier B.V. All rights reserved.