Polynuclear NiII and MnII azido bridging complexes.: Structural trends and magnetic behavior

The azide anion is a good bridging ligand for divalent metal ions, mainly Cu-II, Ni-II and Mn-II. It may give end-to-end (1,3) or end-on (1,1) coordination modes. As a general trend, the 1,1 mode exhibits ferromagnetic coupling while the 1,3 mode creates antiferromagnetic coupling. This review focuses on polynuclear Ni-II and Mn-II azido bridging complexes. Polynuclear structures known to have these two cations are: discrete (normally dinuclear), one-, two- and three-dimensional nets. The main characteristics of these structures are reported together with their magnetic behavior. From a large number of known structures, magneto-structural correlations are made. Taking into account that M-N-3, distances are always similar, the angles within the M-(N-3)(n)-M unit are the main determinant of the type and magnitude of the exchange coupling. Moreover, some one-, two- and three-dimensional complexes exhibit cooperative effects (long-range magnetic order), behaving as molecular magnets. This behavior is also analyzed. (C) 1999 Elsevier Science S.A. All rights reserved.