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Publication Type
Journal Article
UWI Author(s)
Author, Analytic
Maragh, Paul T.,; Dasgupta, Tara, P.; Williams, David J.
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Article Title
Kinetics of the formation, reactivity and crystal structure of the sulfite-bridged cation di-m (sulfito-O,O')-bis[(1, 4, 7-triazacyclononane) chromium (III)
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Connective Phrase
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Journal Title
Journal of the Chemical Society. Dalton Transactions
Translated Title
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Reprint Status
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Date of Publication
1995
Volume ID
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Issue ID
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Page(s)
2843-2849
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Location/URL
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ISSN
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Notes
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Abstract
The kinetics of the formation of [(tacn)Cr(-OH)2(-OSO2)Cr(tacn)]2+ (tacn = 1,4,7-triazacyclono-nane) from trans-[(H2O)(tacn)Cr(-OH)2Cr(tacn)(H2O)]4+ in aqueous buffered sulfite solution have been studied spetrophotometrically, The formation takes place in two steps. The first step which is a rapid uptake of SO2 was studied at 532 nm in the range 1.82 pH 5.93, 0.03 [S]t 0.05 mol dm-3 ([S]t = [SO2] + [SO2-]) and 19.9 q 29.9C. The rate constant for SO2 uptake at 25.2C was found to be 2.10 0.09 dm3 mol-1 s-1 with DH = 94 2 kJ mol-1 and DS = 110 8 J K-1 mol-1. The second step in the formation is the pH- independent isomerization of the trans-aqua-sulfito species, to the cis analogue [Kiso = (4.5 0.1) x 10-3 s-1, 25.2C]; followed by fast unobserved ring-closure step. The sulfido-bridged product undergoes hydroxo bridge cleavage in acid solution (0.030 [H+] 1.0 mol dm-3) to form cis-[(H2O) (tacn)Cr(-OH)(-O2SO)Cr(tacn)(H2O)]3+ in which the sulfite bridge remains intact [k = (6.1 0.1) x 10-2 s-1, 30.0C]. The crystal structure of [(tacn)Cr(-OH)2(-O2SO)Cr(tacn)] [C1O4]2.3H2O shows that the sulfite moiety is bridging the two metal centres via two of its oxygen atoms with partial inversion of the sulfur....
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