Exchange interactions in azido-bridged ligand Ni(II) complexes: a theoretical analysis.

The exchange-coupling constants in dinuclear 1,1-azidonickel(II) complexes and in one tetranuclear complex have been analyzed by using electronic structure calculations based on density functional theory. The calculated J values show a correlation with the Ni-N-Ni angle; however, the available experimental data do not present a correlation between both magnitudes. Hence, new fitting procedures were carried out to obtain a new set of fitted exchange-coupling constants for all of the reported complexes. These new values show a better correlation with the Ni-N-Ni angle close to that found with theoretical methods; however, the calculated values are slightly overestimated. Experimental and theoretical results indicate that, in the range of the experimental values of the Ni-N-Ni angle (90-105 degrees), the strength of the ferromagnetic coupling increases for larger Ni-N-Ni bond angles.