Study on the Photoluminescent and Thermal Properties of Zinc Complexes with a N₆O₄ Macrocyclic Ligand

Abstract

Reactions between a N₆O₄ macrocyclic ligand (L¹) and several Zn(II) salts (trifluoromethane sulfonate, p-toluenesulfonate, acetate, benzoate, o-, m- or p-hydroxybenzoate) led to the formation of seven complexes, [Zn₂L¹ (DMSO)₄](OSO₂CF₃)₄ (1), [Zn₂(p-OSO₂PhCH₃)₄L¹] (2), [Zn₂(OCOCH₃)₄L¹] (3), [Zn₂(OCOPh)₄L¹] (4), [Zn₂(o-OCOPhOH)₄L¹] (5), [Zn₂(m-OCOPhOH)₄ L¹] (6) and [Zn₂(p-OCOPhOH)₄ L¹] (7), which were characterized by elemental analysis, ¹H-NMR, ¹³C-NMR, IR, fluorescence spectroscopies and single crystal X-ray diffraction. In 1, the Zn atom is pentacoordinated with a N₃O₂ irregular trigonal bipyramidal coordination environment, like the geometries in compounds 3⁻7, whereas in structure 2 the metal atom is envisaged as possessing a distorted N₃O₃ octahedronal environment. All the compounds show interesting photoluminescent properties in solid states and solutions in DMF and DMSO, which are reported along with their TG-DTA thermal decomposition processes, UV-vis absorption spectroscopy and fluorescence quantum yields in DMF and DMSO.

Keywords: macrocyclic ligand; photoluminescent properties; thermal properties; zinc complexes.

Scheme 1

Synthetic routes for compounds 1–7.

Figure 1

Thermal ellipsoid plot, drawn at the 50% probability level, of [Zn₂(OS(CH₃)₂)₄L¹]⁴⁺ (1) with atomic numbering scheme. All H atoms and the counterions are omitted for clarity. Symmetry codes: A 1 − x, −y, −z. Selected bond lengths (Å) and angles (°): Zn1-N1 2.1484(18), Zn1-N2 2.084(2), Zn1-N3 2.0922(18), Zn1-O1 2.0399(17), Zn1-O2 2.0556(16); N1-Zn1-N2 83.01(6), N2-Zn1-N3118.58(7), N1-Zn1-N3 84.43(7), O1-Zn1-O2 84.80(7).

Figure 2

Thermal ellipsoid plot, drawn at the 50% probability level, of [Zn₂(p-OSO₂PhCH₃)₄L¹] (2) with atomic numbering scheme. All H atoms, along with DMF, C₄H₈O₂, are omitted for clarity. Symmetry codes: A 1 − x, 1 − y, −z. Selected bond lengths (Å) and angles (°): Zn1-N1 2.122(18), Zn1–N2 2.168(2), Zn1-N3 2.182(2), Zn1–O1 2.4094(19), Zn1–O4 2.086(2); Zn1–O13 2.0390(18); N1–Zn1–N2 82.36(8), N2–Zn1–N3 158.21(8), N1–Zn1–O13 169.81(8), O1–Zn1–O4 174.32(7).

Figure 3

Thermal ellipsoid plot, drawn at the 50% probability level, of [Zn₂(OCOCH₃)₄L¹] (3) with atomic numbering scheme. All H atoms, along with DMFs and waters are omitted for clarity. Symmetry codes: A 1 − x, −1 − y, −z. Selected bond lengths (Å) and angles (°): Zn1–N1 2.0968(14), Zn1–N2 2.218(14), Zn1-N3 2.2024(14), Zn1-O1 1.9456(13), Zn1-O3 2.0184(13); N1–Zn1–N2 80.46(5), N2–Zn1–N3 151.42(5), N1–Zn1–N3 81.50(5), O1–Zn1–O3 100.98(6).

Figure 4

Thermal ellipsoid plot, drawn at the 30% probability level, of [Zn₂(OCOPh)₄L¹] (4) with atomic numbering scheme. All H atoms, along with the solvents are omitted for clarity. Symmetry codes: A 1 − x, −y, −z. Selected bond lengths (Å) and angles (°): Zn1–N1 2.116(3), Zn1–N2 2.177(3), Zn1–N3 2.237(3), Zn1–O1 1.991(2), Zn1–O3 1.979(2); N1–Zn1–N2 80.80(13), N1–Zn1–N3 79.70(12), N2–Zn1–N3 156.08(12), O1–Zn1–O3 109.48(11).

Figure 5

Thermal ellipsoid plot, drawn at the 50% probability level, of [Zn₂(o-OCOPhOH)₄L¹] (5) with atomic numbering scheme. All H atoms, along with the solvents are omitted for clarity. Symmetry codes: A −x, 1 − y, 1 − z. Selected bond lengths (Å) and angles (°): Zn1–N1 2.096(3), Zn1–N2A 2.260(3), Zn1–N3 2.236(3), Zn1-O1 1.995(3), Zn1–O4 1.980(3); N1–Zn1–N2A 80.21(12), N2A–Zn1–N3 155.18(13), N1–Zn1–N3 79.96(10), O1–Zn1–O4 105.97(13).

Figure 6

Thermal ellipsoid plot, drawn at the 50% probability level, of [Zn₂(m-OCOPhOH)₄L¹] (6) with atomic numbering scheme. All H atoms, along with the solvents are omitted for clarity. Symmetry codes: A 2 − x, 1 − y, 1 − z. Selected bond lengths (Å) and angles (°): Zn1–N1 2.063(3), Zn1–N2 2.298(2), Zn1–N3 2.275(2), Zn1–O1 1.994(2), Zn1–O4 1.953(2); N1–Zn1–N2 80.38(10), N2–Zn1–N3 158.43(10), N1–Zn1-N3 80.26(10), O1–Zn1–O4 113.13(9).

Figure 7

Thermal ellipsoid plot, drawn at the 30% probability level, of [Zn₂(p-OCOPhOH)₄L¹] (7) with atomic numbering scheme. All H atoms, along with the solvents are omitted for clarity. Symmetry codes: A −x, −y, −z. Selected bond lengths (Å) and angles (°): Zn1–N1 2.096(3), Zn1–N2 2.202(3), Zn1–N3 2.242(4), Zn1–O1 1.977(3), Zn1–O4 1.971(3); N1–Zn1–N2 81.27(14), N2–Zn1–N3 157.98(12), N–Zn1–N3 80.23(13), O1–Zn1–O4 118.13(12).

Figure 8

The TG-DTA curves of compound 1.

Figure 9

The TG-DTA curves of compound 2.

Figure 10

Solid state emission spectra of L¹ and complexes 1–7 at room temperature (the determination of compound 4 was run with a small amount of samples, a few mg, and under conditions of the narrow slits of emission and excitation than other compounds). The peak of emission is 413 nm for L¹, 463 (1), 462 (2), 383 (3), 390 (4), 425 (5), 388 (6), 411 (7), respectively.