Synthesis, Stability Constant Determination, and Structural Study of Some Complexes of a Zinc Triad Containing Pyridyl‐amine‐quinoline and Pyridyl‐thio‐quinoline

Abstract

Keywords: Zinc / Quinoline-based ligands / Fluorescence / Formation constantsThe potentially fluorescent and terdentate ligands containing nitrogen or sulfur as coordinating atom were synthesized and used in the formation of perchlorate or chloride complexes of the metals of the Zn triad. The reaction of the ligands with metal perchlorate salts yields the corresponding bis-chelate derivatives, whereas the same ligands react with metal chloride salts to give monochelate complexes. All of these complexes undergo NMR-scale fast fluxional rearrangement in solution. Some structural X-ray diffractometric studies were also performed and the ensuing data confirm the surmised structures and the solution rearrangement in the case of monochelate substrates and of one Hg derivative, respec-

Luminescent complexes of the zinc triad with N-substituted 8-amino-quinoline ligands: Synthesis and comparative study on the stability constants and related photophysical properties

“…The most prominent aspect of the 1 H NMR spectra of the ensuing complexes in CD 3 CN is represented by the high-field shift of the H 2 quinoline protons upon coordination. Such a behavior, which is not unprecedented, was already discussed in previous works and was traced back to the anisotropic shielding of the H 2 protons due to the p-delocalized electrons of the close aromatic rings belonging to the opposite ligand [4,8]. However, at variance with the 1 H NMR spectra of the complexes published elsewhere [4] and with that of the comparable species [Zn(NNN (Qui) Comparison with the complexes of the X group with the same BQA ligand shows the utter unpredictability of the resonance position of that signal which can be shielded, isochronous or deshielded with respect to the signal of the uncoordinated ligand in the case of Ni, Pd and Pt, respectively [5].…”

“…The acidity of the aminic proton of the ligand BQAH (pK a = 11.4 in solution of CH 3 CN:H 2 O 1:1 v:v) [6] is somewhat higher than that of the NNN(Qui) moiety which gives no hints of dissociation in water even when coordinated [4]. Such an acidity is increased upon coordination to the cationic center and the deprotonated spe- Strictly speaking b and b * are not directly comparable since the latter represents the product of different constants (i.e.…”

“…In order to compare the behavior of BQAH with that of the ligands previously studied [4] we have re-determined the formation constants of the zinc triad metals with the ligand NNN(Qui) in CH 3 CN.…”

“…For the sake of completeness and as an internal check of consistency the formation constants of the complexes of the NNN(Qui) ligand already determined in water [4] were re-determined in acetonitrile. Unfortunately, the spectrophotometric titration of the ligand NNN(Qui) with Hg(ClO 4 ) 2 was unsuccessful owing to the random response of the absorbance data upon Hg(ClO 4 ) 2 addition.…”

“…Recently, we have published a paper dealing with the synthesis of some amine and thioether pyridine and quinoline derivatives in which their coordinative and photophysical properties when coordinated to zinc, cadmium and mercury were analyzed in detail [4]. We have now extended our investigation to the ligand di-quinolin-8-yl-amine (BQAH) with the aim of increasing the fluorescence intensity of the ensuing metal complexes.…”