Mononuclear and Tetranuclear Compounds of Yttrium
and Dysprosium Ligated by a Salicylic Schiff-Base Derivative: Synthesis,
Photoluminescence, and Magnetism
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Abstract
The Schiff-base (2-aminoethyl)hydroxybenzoic
acid (H<sub>2</sub>L) as a proligand was prepared in situ from 3-formylsalicylic
acid
and ethanolamine (ETA). The mononuclear {[Y(HL)<sub>4</sub>][ETAH]·H<sub>2</sub>O} (<b>1</b>) and {[Dy(HL)<sub>4</sub>] [ETAH]·3MeOH·H<sub>2</sub>O} (<b>2</b>) and tetranuclear {[Y<sub>4</sub>(HL)<sub>2</sub>(L)<sub>4</sub>(μ<sub>3</sub>-OH)<sub>2</sub>]·4MeOH·4H<sub>2</sub>O} (<b>3</b>), {[Dy<sub>4</sub>(HL)<sub>2</sub>(L)<sub>4</sub>(μ<sub>3</sub>-OH)<sub>2</sub>]·5(MeOH)<sub>2</sub>·7H<sub>2</sub>O (<b>4</b>), and {[Dy<sub>4</sub>(HL)<sub>8</sub>(L)<sub>2</sub>]·4MeOH·2H<sub>2</sub>O}(<b>5</b>) rare-earth metal complexes of this ligand could be obtained as
single-crystalline materials by the treatment of H<sub>2</sub>L in
the presence of the metal salts [Ln(NO<sub>3</sub>)<sub>3</sub>·(H<sub>2</sub>O)<sub><i>m</i></sub>] (Ln = Y, Dy). In the solid
state, the tetranuclear compounds <b>3</b> and <b>4</b> exhibit butterfly structures, whereas <b>5</b> adopts a rectangular
arrangement. Electrospray ionization mass spectrometry data of the
ionic compounds <b>1</b> and <b>2</b> support single-crystal
X-ray analysis. The yttrium compounds <b>1</b> and <b>3</b> show fluorescence with 11.5% and 13% quantum yield, respectively,
whereas the quantum yield of the dysprosium complex <b>4</b> is low. Magnetic studies on the dysprosium compounds <b>4</b> and <b>5</b> suggest the presence of weak antiferromagnetic
interactions between neighboring metal centers. Compound <b>4</b> shows single-molecule-magnet behavior with two relaxation processes,
one with the effective energy barrier <i>U</i><sub>eff</sub> = 84 K and the preexponential factor τ<sub>0</sub> = 5.1 ×
10<sup>–9</sup> s
