ISSN:
1573-1111
Schlagwort(e):
Barium
;
benzo-15-crown-5
;
chelating organic anion
;
counteracting anion effect
;
X-ray diffraction analysis
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
Abstract The interaction of barium with benzo-15-crown-5 (B15C5) has been followed under the competitive effect of various chelating organic anions (L), nitrophenolates and nitrobenzoates, in ethanol and ethanol-water (9:1). The rather heavily hydrated BaL2 salts yield novel 1:1 stoichiometric products in monohydrated or anhydrous states. Use of excess crown does not under any condition lead to the formation of 1:2 charge separated complexes, expected in view of the cavity and the cation sizes. The 1:1 Ba−B15C5 interaction is counteracted by L in accordance with its nucleophilicity, i.e., the pK a value of its parent acid, HL. The complex Ba(picrate)2(B15C5)·H2O (BaC26H26N6O20, FW=879.0), is monoclinic,P21/c,a=11.43(1),b=16.31(3),c=17.38(2) Å, β=92.265(3)°,Z=4,D c=1.77 g/cm3,D 0=1.73 g/cm3, MoKα, λ=0.71069 Å, 2θ (4.0–50°), μ=13.5 cm−1,F(000)=1752,T=−32°C. FinalR for the 5926 reflections was 0.049. The structure reveals barium to be 10-coordinated through all the five crown oxygens (Ba−O, 2.800 to 3.002 Å), the two bidentate picrates (Ba−O, 2.642 and 2.666 Å; Ba−ONO, 2.825 and 2.994 Å), and the water molecule (2.711 Å) so that the cation constitutes a pseudo-sandwich of the crown on one side and the anionic species on the other.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00665475
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