The Photochemistry of [Co(CN)5X]n- complexes
Date
2018-06-29
Authors
Kneeland, Diane M.irgaret
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Abstract
Irradiation of [special characters omitted] at 313 nm in basic solution at 10°C in the presence of free SCN yields the products [special characters omitted], and [special characters omitted]. Analysis of product distribution was done by HPLC using a [special characters omitted] column and ion pairing reagents with methanol and water as the eluent. The aquation/anation product ratio is independent of X, but depends linearly on the concentration of SCN. A specific ion effect is observed, the aquation/anation ratio showing a correlation with the radius of the cation. The ratio of sulfur to nitrogen thiocyanato product is 10±2, independent of X, concentration of SCN, and cation, but is different that measured in the thermal anation of [special characters omitted] which gives a S/N ratio of 4. A limiting dissociative mechanism is proposed for the photosubstitution, involving a five coordinate intermediate of sufficient kinetic stability to discriminate among entering groups. The constant S/N ratio for the photosubstitution leads to the conclusion that the intermediate formed in the photoreaction is different from that formed in the thermal reaction. Direct anation has been reported previously for aquopentacyanocobaltate, but not for hexacyanocobaltate. Quenching of the emission lifetime of [special characters omitted] in the presence of chloride salts shows the same order of cation assistance with cation radius as observed for the aquation/anation ratio.
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Keywords
Coordination compounds, Ligands, Photochemistry