Crystal structures and photophysical properties of mono- and dinuclear ZnII complexes flanked by tri-ethyl-ammonium

Abstract

Two new zinc(II) complexes, tri-ethyl-ammonium di-chlorido-[2-(4-nitro-phen-yl)-4-phenyl-quinolin-8-olato]zinc(II), (C₆H₁₆N){Zn(C₂₁H₁₃N₂O₃)Cl₂] (ZnOQ), and bis-(tri-ethyl-ammonium) {2,2'-[1,4-phenyl-enebis(nitrilo-methyl-idyne)]diphenolato}bis-[di-chlorido-zinc(II)], (C₆H₁₆N)₂[Zn₂(C₂₀H₁₄N₂O₂)Cl₄] (ZnBS), were synthesized and their structures were determined using ESI-MS spectrometry, ¹H NMR spectroscopy, and single-crystal X-ray diffraction. The results showed that the ligands 2-(4-nitro-phen-yl)-4-phenyl-quinolin-8-ol (HOQ) and N,N'-bis-(2-hy-droxy-benzyl-idene)benzene-1,4-di-amine (H₂BS) were deprotonated by tri-ethyl-amine, forming the counter-ion Et₃NH⁺, which inter-acts via an N-H⋯O hydrogen bond with the ligand. The Zn^II atoms have a distorted trigonal-pyramidal (ZnOQ) and distorted tetra-hedral (ZnBS) geometries with a coord-ination number of four, coordinating with the ligands via N and O atoms. The N atoms coordinating with Zn^II correspond to the heterocyclic nitro-gen for the HOQ ligand, while for the H₂BS ligand, it is the nitro-gen of the imine (CH=N). The crystal packing of ZnOQ is characterized by C-H⋯π inter-actions, while that of ZnBS by C-H⋯Cl inter-actions. The emission spectra showed that ZnBS complex exhibits green fluorescence in the solid state with a small band-gap energy, and the ZnOQ complex does exhibit non-fluorescence.

Keywords: 8-hy­droxy­quinoline derivatives; Schiff base.; Zn(II) complex; crystal structure.

Figure 1

The mol­ecular structure of ZnOQ showing the atom-labeling scheme and displacement ellipsoids at the 30% probability level. The N—H⋯O hydrogen bond is shown as a red dashed line.

Figure 2

The mol­ecular structure of ZnBS showing the atom-labeling scheme and displacement ellipsoids at the 30% probability level. The N—H⋯O hydrogen bonds are shown as a red dashed line. Symmetry code: (i) −x + 1, −y + 1, −z + 2.

Figure 3

Partial crystal packing of ZnOQ showing the C—H⋯π and N—O⋯π inter­actions as gray dashed lines. The N—H⋯O hydrogen bond is shown as a red dashed line. Further details are given in Table 1 ▸. For clarity, hydrogen atoms not involved in hydrogen bonding are omitted and the tri­ethyl­ammonium ion is shown in pink.

Figure 4

Partial crystal packing of ZnBS showing the C—H⋯Cl inter­actions as gray dashed lines. The N—H⋯O hydrogen bond is shown as a red dashed line. Further details are given in Table 2 ▸. For clarity, hydrogen atoms not involved in hydrogen bonding are omitted and the tri­ethyl­ammonium ion is shown in pink.

Figure 5

Chain formation in the b-axis direction by C—H⋯Cl inter­actions (gray dashed lines) in the crystal packing of ZnBS.

Figure 6

Search fragments used in Conquest to perform the CSD survey: (a) five-membered ring fragment present in ZnOQ, (b) six-membered ring fragment present in ZnBS.

Figure 7

(a) Absorption and (b) emission spectra in the solid state at λ_ex = 425 nm of H₂BS and ZnBS.

Figure 8

Synthesis of the complexes (a) ZnOQ and (b) ZnBS.