. Can. J. Chem. 58, 1651 (1980). X-ray diffraction studies have revealed that K4U02(C03), is isostructural with (NH,),UO,(CO,),; the crystal is monoclinic with a [Traduit par le journal]
The binding of Mn2+ to a well characterized fulvic acid sample is reported based on the competition with K+ in an ion exchange equilibration. The free energy of binding of [Formula: see text] to fulvic acid is only 1–2 kJ/equivalent more favourable than that for K+. This suggests an outer sphere electrostatic structure for the complex. The suggestion is confirmed by observation of minimal change in the presence of fulvic acid of the effect of paramagnetic Mn2+ on the nmr spectra of water. The interpretation of nmr spectra is supported by comparison with nmr measurements of Mn2+ complexes with simple ligands and contrast with nmr measurements on Fe3+ – fulvic acid complexing. The latter is confirmed as inner sphere.
W e report new measurements adding to the literature o n solvent and counter ion dependence of ' OF-chemical shift. These are compared to earlier r e s~~l t s for "'CI-, "'Br-, anel "'I-. The observations support the following points: ( 1 ) there a r e few systematic differences between behavior of anion shifts in dilute and nioclerately concentrated aqueous solution, ( 2 ) anion shifts c o n~n~o n l y show larger sensitivity to solvent than counter ion over convenient ranges of variation so that "solvent shift" may be easily measurecl. Using the concept of collision effects on shifts cleveloped by Richards and his collaborators, it is possible to separate, in many cases, the large effects arising f r o m contact, or primary solvation sphere, collisions from the smaller effects of outer sphere interactions.W e find no preferential solvation of F-by H.0 in mixtures with CH:,OH; at most, small preferecce over CI.H,OH and formamide, and a small opposite preference in favor of diols. However, water appears strongly preferred in the primary solvation shell over acetone, acetonitrile, dioxane, and (in contrast t o other ha!ides), clin~ethylsulfoxicle. Solvation by amines involving both outer and inner sphere site occupation is considered.T h e inter-anion effects on fluoride ion chemical shifts tend to undermine the concept of additivity of ionic effects o n shifts.
In the kinetic literature, an embarrassing ambiguity has plagued many distinguished authors. When a reaction seems to demand participation of a solute and a solvent molecule in a way parallel to bimolecular gas-phase reaction, the question arises: can a second-order rate constant be calculated by dividing an observed first-order rate constant by the molar concentration (or the activity) of the solvent?Such second-order rate constants are frequently calculated, but the authors usually express some malaise. This malaise arises from the fact that a careful Cooper H. Langford was born at Ann Arbor, Mich., in 1934. He holds an A. B. degree from Harvard and a Ph.D. from Northwestern. He has taught at Amherst College and as a visitor at Columbia. He is now settled in Canada and has been Professor of Chemistry at Carleton University since 1967. James P. K. Tong was born in Hong Kong in 1947. He was awarded an honors B.Sc. at McGill in 1969. He completed his Ph.D. at Carleton in 1974 and is presently a postdoctoral fellow at McMaster University. Drs. Langford and Tong are interested in reaction mechanisms in inorganic chemistry and inorganic photochemistry as well as NMR studies of solvation.
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