Structure and ion-complexing properties of an aza-15-crown-5 ether dye: synthesis, crystallography, NMR spectroscopy, spectrophotometry and potentiometry

Abstract

The perchlorate of 2-{2-[4-(13-aza-1,4,7,10-tetroxa-13-cyclopentadecyl)phenyl]ethenyl}-3-ethylbenzothiazolium (3) has been synthesised and its structure determined in the crystalline state by X-ray diffraction and in solution in acetonitrile by 1 H NMR methods. Complexation with barium and silver cations in solution has been studied in comparison with other model azacrown molecules by spectrophotometric and potentiometric methods. With the exception of the puckered azacrown moiety, the structure of 3 is remarkably planar, consistent with extensive -conjugation throughout the remainder of the molecule in both solid and solution states. Compound 3 forms a stable 1 : 1 complex with Ba 2ϩ ions in acetonitrile, with a stability constant of K 1 = 80 ± 10 dm 3 mol Ϫ1 ; the complexation results in major changes in the electronic absorption spectrum of 3, consistent with binding to the azacrown moiety. A model compound, phenylaza-15-crown-5 (2a), was found to bind Ba 2ϩ to form both a 1 : 1 ligand-metal complex (LM), with a stability constant of K 1 = (2.0 ± 0.2) × 10 4 dm 3 mol Ϫ1 , and a 2 : 1 (L 2 M) complex, with a stability constant of K 2 = 220 ± 20 dm 3 mol Ϫ1 for binding of the second ligand. The electronic absorption and NMR spectra both indicate binding of the 'hard' Ba 2ϩ cation to the azacrown oxygen atoms. However, by contrast, the evidence from NMR data shows that the 'soft' Ag ϩ cation complexes with 2a mainly through a strong interaction with the azacrown nitrogen atom, giving a 1 : 1 complex with a stability constant of K 1 = 6 ± 1 dm 3 mol Ϫ1 , determined by potentiometry. No complexation of 3 with Ag ϩ is observed. Studies of the simple aza-15-crown-5 ether reveal strong complexation with both Ba 2ϩ (K 1 × K 2 > 10 12 dm 6 mol Ϫ2 ) and Ag ϩ [K 1 = (1.15 ± 0.10) × 10 4 dm 3 mol Ϫ1 and K 2 = 450 ± 20 dm 3 mol Ϫ1 ].

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study 2.* Effect of the metal ion— solvent interaction on the conformations of calcium complexes of arylazacrown ethers

“…25 The greatest deviation of the calculated geomet ric parameters of the free dye from the corresponding experimental values was observed for the C=C double bond (~2%). Within the chromophore moiety, the C-N cr bond length in the axial conformers of the complex un dergoes the most pronounced change in complexation (up to ~0.1 Å).…”

Transition Metal Ion Complexes of 2,2′-Bipyridyl-3,3′-diol and 2,2′-Bipyridyl-3-ol: Spectroscopic Properties and Solvent-Dependent Binding Modes

“…In all the UV/vis spectrophotometric and fluorometric titrations performed with BP(OH) 2 and various metal ions, no divergent spectral features were found, making a discrimination between the 1:1 and 1:2 complexes impossible in this way. However, fitting the titration curves was only found to yield acceptable results for a sum of a 1:1 and a 2:1 complexation model [34] in some cases (Zn II , Cd II ), both complexes showing similar spectroscopic behaviour. For the other, more strongly coordinating ions, the complex stability constants are too high to be reliably determined by this method and the relatively poor solubility of BP(OH) 2 in terms of a c L0 titration (see Experimental Section) made such a reverse titration (titration of M with L) impossible.…”

Spacer-chromoionophores - polymethine dye substituted aza-crown ethers with increased complexation ability

“…Found: C 59.17 H 6.14 N 10.84. (2,3,5,6,8,9,11, [1,4,7,10,13 (2,3,5,6,8,9,11,12- 8 mmol) of sodium carbonate were suspended in 3 ml of absolute ethanol, and the mixture was heated under reflux for 40 h. After cooling the solution was filtered, and the precipitate washed with 15 ml of dichloromethane. The filtrate was concentrated, the residue dissolved in 15 ml of dichloromethane, and washed twice with water.…”