Slow magnetic relaxation in 8-coordinate Mn(II) compounds

The design and synthesis of high-spin Mn(II)-based single-molecule magnets (SMMs) have not been well developed to a great extent, as compared with a large number of SMMs based on the other first row transition metal complexes. In light of our success in designing Fe(II), Co(II) and Fe(III)-based SMMs with a high coordination number of 8, it is of great interest to design Mn(II) analogues with such a strategy. In this contribution, four Mn(II) compounds, [Mn^II(Ln)₂](ClO₄)₂ (1-4) were obtained from reactions of neutral tetradentate ligands, L1-L4, with hydrated Mn^II(ClO₄)₂ (L1 = 2,9-bis(carbomethoxy)-1,10-phenanthroline, L2 = 2,9-bis(carbomethoxy)-2,2'-dipyridine, L3 = N²,N⁹-dibutyl-1,10-phenanthroline-2,9-dicarboxamide, L4 = 6,6'-bis(2-(tert-butyl)-2H-tetrazol-5-yl)-2,2'-bipyridine). Their crystal structures have been determined by X-ray crystallography and it clearly shows that the Mn(II) centers in these compounds have an oversaturated coordination number of 8. Their magnetic properties have been investigated in detail; to our surprise, all of these Mn(II) compounds show interesting slow magnetic relaxation behaviors under an applied direct current field, although they have very small negative D values.