The stability constants of 1:l "supercomplexes" formed between the three large, variously protonated, polyazacycloalkanes 1,4,7,10,13,16,19,22,25-nonaazacycloheptacosan(eL I), 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontan(eL Z), and 1,4,7,10,13,16,19,22,25,28,31-undecaazacyclotritriacontane(L 3) and the anions [Fe(CN),]' and [Co(CN),I3- have been determined by potentiometry at 25 OC in 0.15 NaC104. Many species are formed, and the anion [Fe(CN),]+ forms "supercomplexes" that are more stable than the corresponding species involving the less charged anion [Co(CN),13-. In the case of "supercomplexes" involving [Fe(CN),]', the CV technique was applied to confirm potentiometric studies. Results are discussed assuming that Coulombic forces are the most important factor which governs the formation of these "supercomplexes". The molecular structure of the "supercomplex" [H8L2] [CO(CN)&C12*1OH20 has been determined by single-crystal X-ray analysis. The compound crystallizes in the Pi space group with a = 14.818 (3) A, b = 10.414 (2) A, c = 8.974 (2) A, CY = 78.68(1)', 0 = 85.99 (1)O, y = 89.67 (2)", and 2 = 1. Refinement of the atomic parameters by least squares gave a final R factor of 0.075 (R, = 0.074) for 3178 unique reflections having I > 3 4 ) . The structure consists of discrete (H8L2)8t cations, [Co(CN),I3- anions outside the macrocyclic cavity, chloride anions, and water molecules. The macrocycle displays an elongated elliptical shape, and its conformation appears essentially imposed by the strong Coulombic repulsions between the positively charged nitrogen atoms, which form two stiff parallel chains. There are two unprotonated nitrogen atoms on opposite sides of the cycle. Several hydrogen bonds are formed between the cyanide groups of one of the hexacyanocobaltate(II1) anions and the macrocyclic nitrogen atoms. The hydrogen-bonding scheme is completed by several other bonds involving chloride anions and water molecules.
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|Titolo:||Anion Coordination Chemistry .2. Electrochemical, Thermodynamic, and Structural Studies On Supercomplex Formation Between Large Polyammonium Cycloalkanes and the 2 Complex Anions Hexacyanoferrate(ii) and Hexacyanocobaltate(iii)|
|Citazione:||A., B., A., B., E., G., M., G., Mangani, S., M., M., et al. (1987). Anion Coordination Chemistry .2. Electrochemical, Thermodynamic, and Structural Studies On Supercomplex Formation Between Large Polyammonium Cycloalkanes and the 2 Complex Anions Hexacyanoferrate(ii) and Hexacyanocobaltate(iii). INORGANIC CHEMISTRY, 26, 3902-3907.|
|Appare nelle tipologie:||1.1 Articolo in rivista|