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.