Packing Structure Effects on the Slow Magnetic Relaxation Pathways of Dysprosium (III) Complexes

Three complexes, [Dy{5-(5-methylthiophen-2-yl)-2,2- bipyridine}(hfac)3] (6), [Dy{5-(4-bromo-5-methylthiophen-2- yl)-2,2-bipyridine}(hfac)3] (7) and [Dy{5-(4-ethynyl-5-methylthio- phen-2-yl)-2,2-bipyridine}(hfac)3] (8) (hfac = hexafluoroacetylacetate), were synthesized to investigate the effects of substituents on the ligand far from the metal ion on the magnetic properties of the dysprosium ion. 7 crystallized in two polymorphs (P21/n for 7a and P21/a for 7b), whereas 6 and 8 crystallized in one polymorph (P21/n and P21/a, respectively). All of the complexes have columnar structures, and in 6 and 7a, there are stacking interactions between neighboring aromatic rings in contrast to compounds 7b and 8, which do not show such interactions. Every complex underwent slow magnetic relaxation with a single relaxation time, except for complex 7a, for which there were two relaxation times. In order to clarify the role of distal substitution and crystal packing, the magnetic properties were studied in solution, where all of the complexes show single relaxation times.