Nuclear magnetic resonance relaxation studies on the preferential solvation of tris-acetylacetonato–chromium(III) in bromoform–carbon tetrachloride solutions

Abstract

N.m.r. relaxation has been used to study the solvation of tris-acetyl-acetonoato-chromium(III)[Cr(acac)₃] with bromoform in solutions. The temperature-dependent stability constant of the solvated complex has been determined in the region of dilute bromoform solutions. The results have been used to interpret the deuteron relaxation data in the corresponding perdeuterated solution of Co(acac)₃. A solvation number of two is found in the temperature range 285–325 K. The distance between the chromium ion and the proton (or carbon atom) of solvated bromoform was found to be 3.6 Å( or 4.6 Å). This evidence indicates the formation of a trifurcated hydrogen bond between bromoform and the acetylacetonato complex. Compared with the chloroform solvent system, larger stability constants have been found in this study. The results are successfully applied to the estimation of deuteron relaxation rates in the perdeuterated solutions of Cr(acac)₃ and to the evaluation of the differential line broadening effects on deuteron split ¹³C triplets of CDBr₃ molecules.