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 (L1/2)− 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 (L1/2)− ligands, but the arrangements of the three ligands are different owing to the methyl substituent on HL2. There are three short predominant Dy–Ophenoxy bonds in 2 and 3. The largest Ophenoxy–Dy–Ophenoxy 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 (Ueff = 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–Ophenoxy bonds affects the magnetic anisotropy of the Dy(III) ions and relaxation processes of complexes 2 and 3.