Magnetic properties of transition metal (Mn(II), Mn(III), Ni(II), Cu(II)) and lanthanide (Gd(III), Dy(III), Tb(III), Eu(III), Ho(III), Yb(III)) clusters and [nxn] grids: Isotropic exchange and SMM behaviour

摘要

Polyfunctional hydrazone ligands have provided a wealth of examples of polynuclear grids and clusters based on self-assembly strategies, where simple design elements built into the ligand backbones provide the coordination instructions. The combination of hydrazone oxygen, diazine and terminating N donor functional groups creates coordination options for metals ions which generally, as a result of coordinative unsaturation, do not allow for the ligand to chelate to a single metal ion. Instead the metal achieves coordination completion by aggregation processes where clusters form from multiple combinations of ligands and metal ions, using mu(2)-O-hydrazone, and mu(2)-N-2 diazine groups as potential bridges. Examples of transition metal and lanthanide clusters in the range M-3, M-4, M-6, M-9, M-12 and M-16 will be discussed, with magnetic properties interpreted using fully isotropic models in some cases, and approximations where spin state calculations exceed the computer's capacity to handle the enormous matrices involved. In the case of some Dyn complexes SMM (single molecule magnet) behaviour is observed, with relaxation properties interpreted using field and temperature dependent AC measurements. (C) 2014 Elsevier B.V. All rights reserved.