Hybrid Pyridine Bis -Anthracene-Imidazolium Salt: NMR Studies on Zn-Acetate Complexation Hybrid Pyridine Bis -Anthracene-Imidazolium Salt: NMR Studies on Zn-Acetate Complexation

: We report here the design and synthesis of a new hybrid bis -anthracene-imidazolium salt, having a pyridine scaffold. NMR studies of dimer generation, as well as complexation with zinc acetate were performed. Abstract: We report here the design and synthesis of a new hybrid bis -anthracene-imidazolium salt, having a pyridine scaffold. NMR studies of dimer generation, as well as complexation with zinc acetate were performed.


Introduction
In the field of supramolecular chemistry, the design and synthesis of chemosensors for the detection of metal ions have been widely exploited, due to their biological and environmental significance [1][2][3]. Most of these receptors can be considered hybrid compounds based on a moiety of imidazole, benzimidazole and pyridine, attached to the fluorophore, which is the anthracene unit [1][2][3][4][5].

Introduction
In the field of supramolecular chemistry, the design and synthesis of chemosensors for the detection of metal ions have been widely exploited, due to their biological and environmental significance [1][2][3]. Most of these receptors can be considered hybrid compounds based on a moiety of imidazole, benzimidazole and pyridine, attached to the fluorophore, which is the anthracene unit [1][2][3][4][5].

of 6
Our expectation was to obtain a complex of ylide 4 with Zn 2+ of type 5, Scheme 2 as in related cases [5]. Instead, because of high reactivity of ylide 4, a dimerisation process took place (via a 3 + 3 dipolar cycloaddition of an ylide molecule to another) when the dimeric structure type 6 was obtained. In the next step, the dimer 6 complexes with Zn 2+ , leading to the final product, the dimer complex with Zn 2+ , type 7. The structure of Zn complex, type 7, is a proposed structure but different coordination of Zn 2+ ion cannot be excluded.
Our expectation was to obtain a complex of ylide 4 with Zn 2+ of type 5, Scheme 2 as in related cases [5]. Instead, because of high reactivity of ylide 4, a dimerisation process took place (via a 3 + 3 dipolar cycloaddition of an ylide molecule to another) when the dimeric structure type 6 was obtained. In the next step, the dimer 6 complexes with Zn 2+ , leading to the final product, the dimer complex with Zn 2+ , type 7. The structure of Zn complex, type 7, is a proposed structure but different coordination of Zn 2+ ion cannot be excluded. In Figure 1 are presented the overlapped 1 H-NMR spectra of salt 3, dimeric structure 6 and dimeric complex with Zn 2+ type 7. Here are described the quantities of reactants used in the experiments and the exchange of the color of solutions. In Figure 1 are presented the overlapped 1 H-NMR spectra of salt 3, dimeric structure 6 and dimeric complex with Zn 2+ type 7. Here are described the quantities of reactants used in the experiments and the exchange of the color of solutions.
In the 1 H-NMR spectrum of dimeric structure type 6 it can be observed the disappearance of protons (-CH 2 -) 6 , which in salt 3 appears as a singlet at 6.48 ppm. Also, the signal around 9.06 ppm of H 2 from imidazole nucleus of salt 3 does not appear in the NMR spectrum of dimer 6.
The dimer complexation with Zn 2+ induces a visible shielding effect on the chemical shifts of the protons from aliphatic and aromatic zone. In the 1 H-NMR spectrum of dimeric structure type 6 it can be observed the disappearance of protons (-CH2-)6′, which in salt 3 appears as a singlet at 6.48 ppm. Also, the signal around 9.06 ppm of H2′ from imidazole nucleus of salt 3 does not appear in the NMR spectrum of dimer 6.
The dimer complexation with Zn 2+ induces a visible shielding effect on the chemical shifts of the protons from aliphatic and aromatic zone.

Instrumentation
The solvents and reagents were purchased from commercial sources, being used without further purification. The melting point (uncorrected) of compound 3 was determined using an open capillary tubes introduced in a MEL-TEMP Electrothermal apparatus. The nuclear magnetic resonance experiments have been recorded on a Bruker AVANCE III 500 MHz spectrometer (Iasi, Romania), equipped with a 5 mm PABBO detection probe, operating at 500.19 and 125.7 MHz for 1 H and respectively 13 C nuclei. In 1 H and 13 C spectra, chemical shifts are reported in δ units (ppm) relative to the residual peak of solvent (ref: DMSO-d6, 1 H: 2.50 ppm; 13 C: 39.52 ppm). The coupling constants (J) are given in Hz. In the NMR spectra to appointed the multiplicity of signals, were used the abbreviations: s = singlet, d = doublet, t = triplet. The microanalyses were in satisfactory agreement with the calculated values: C, ±0.15; H, ±0.10; N, ±0.30.

Instrumentation
The solvents and reagents were purchased from commercial sources, being used without further purification. The melting point (uncorrected) of compound 3 was determined using an open capillary tubes introduced in a MEL-TEMP Electrothermal apparatus. The nuclear magnetic resonance experiments have been recorded on a Bruker AVANCE III 500 MHz spectrometer (Iasi, Romania), equipped with a 5 mm PABBO detection probe, operating at 500.19 and 125.7 MHz for 1 H and respectively 13 C nuclei. In 1 H and 13 C spectra, chemical shifts are reported in δ units (ppm) relative to the residual peak of solvent (ref: DMSO-d 6 , 1 H: 2.50 ppm; 13 C: 39.52 ppm). The coupling constants (J) are given in Hz. In the NMR spectra to appointed the multiplicity of signals, were used the abbreviations: s = singlet, d = doublet, t = triplet. The microanalyses were in satisfactory agreement with the calculated values: C, ±0.15; H, ±0.10; N, ±0.30.

General Procedure for Synthesis of Hybrid Quaternary Salt 3
To a solution of 2,6-bis((1H-imidazol-1-yl)methyl)pyridine 1 (1 mmol, 1 equiv., 0.24 g, dissolved in 40 mL acetone using the ultrasound bath) was added dropwise a solution of 9-(chloromethyl)anthracene 2 (2.8 mmol, 2.8 equiv., 0.63 g, dissolved in 15 mL acetone using the ultrasound bath). The reaction mixture was refluxed for 12 h, and stirred at room temperature for another 24 h to give the corresponding hybrid quaternary salt 3. The completion of the reaction was carried out using TLC. The obtained salt was filtered off, washed two times with the same solvent (10 mL) and dried in vacuum. No other purification required.