Rhodamine Salicylaldehyde Hydrazone Dy(III) Complexes: Fluorescence and Magnetism

Three new dysprosium(III) complexes [Dy₂(HL¹-o)₂(L¹)(NO₃)₃][Dy(NO₃)₅]·1.5ACE·0.5Et₂O (1), [Dy(L¹)₃]·2.5MeOH·MeCN (2), and [Dy(L²)₃]·MeOH·MeCN (3) (HL¹ = rhodamine B salicylaldehyde hydrazine, HL² = rhodamine B 3-methylsalicylaldehyde hydrazine) were synthesized and characterized. Purple complex 1 contains two ring-open ligands HL¹-o and shows fluorescence of the rhodamine amide moiety, whereas yellow complexes 2 and 3 are comprised of ring-close ligands (L^1/2)^- and display fluorescence of the salicylaldehyde Schiff base part. For 2 and 3, Dy(III) ions are nine coordinated by the six oxygen and three nitrogen atoms of three chelate (L^1/2)^- ligands, but the arrangements of the three ligands are different owing to the methyl substituent on HL². There are three short predominant Dy-O_phenoxy bonds in 2 and 3. The largest O_phenoxy-Dy-O_phenoxy angle is 148.64(17)° for 2 and 89.63(13)° for 3. Magnetic studies reveal that complex 2 is a field-induced single-molecule magnet ( U_eff = 104.2 K under a dc magnetic field of 2000 Oe), and 3 exhibits only a magnetic relaxation behavior owing to the quantum tunneling of magnetization (QTM). Furthermore, ab initio calculations illustrate that the disposition of predominant Dy-O_phenoxy bonds affects the magnetic anisotropy of the Dy(III) ions and relaxation processes of complexes 2 and 3.