Electronic structure of the Haldane gap system derived using DV-Xα calculations

The syntheses, X-ray structural analysis, magnetic properties and the electronic structure of Haldane gap system compounds that include Ni(II) ions, are reported. Haldane gap system compounds, such as NINAZ, NDMAZ, NDMAP, NINOP, NINAP and NDMAPen, have been synthesized by substituting different in-plane ligands, bridging ligands and counteranions. The exact X-ray structural analysis of NINAZ has also been carried out for the first time. The correlation between the antiferromagnetic interaction, J, and the Haldane gap, E-g, in these compounds is observed to depend on the particular combination of the counteranions and the in-plane and bridging ligands. The possibility of controlling the Haldane gap can be shown by substituting the bridging (N-3(-) > NO2-) and in-plane (tn > en > linear-tetramines > dmpn > Me-6[14]aneN(4) > [15]aneN(4)) ligands and counteranions (ClO4- > PF6-. From the result of an overlap population analysis using the DV-X alpha calculation method, we have observed a trend that the compound having the large value of Haldane gap, such as NINAZ, has the most well-balanced intramolecular overlap dispersion in the bridging N-3(-) molecule. A new manifestation of the way to predict the value of the Haldane gap can therefore be found by using overlap population analysis by means of the DV-X alpha molecular orbital calculations. (C) 2001 Elsevier Science Ltd. All rights reserved.