Proton magnetic resonance spectra of N-deuterated Co(en)33+ and Co(/?-pn)33+ in D20 at various temperatures and phosphate concentrations were obtained at 251 MHz with spin decoupling of cobalt-59. From the coupling constants obtained by analysis of the Co(en)33+ AA'BB spectra, the fraction of time spent by an ethylenediamine ring in each conformational state (i.e., with carbon-carbon bonds perpendicular or parallel to the C3 axis) is determined. The molecular species having one carbon-carbon bond perpendicular and two carbon-carbon bonds parallel to the C3 axis (e.g., -) is more abundant than the species having all three carbon-carbon bonds parallel to the C3 axis (e.g.,). However, the population ofexceeds that ofat high phosphate concentrations. For efficient cobalt-59 decoupling, the extent of N-deuteration must be extremely high because of large deuterium isotope effects on cobalt-59 chemical shifts, as shown by cobalt-59 magnetic resonance spectra.Nonequivalent methyl resonances and nonequivalent methylene resonances were resolved in the 250-MHz pmr spectra of Co(i?-pn)33+ (cis-trans mixture), and approximate chemical shifts and coupling constants were obtained by first-order analysis.
A series of complex compounds of cobalt(III) involving pentadentate ethylenediaminetriacetic acid, ED3A, as the chelating agent have been prepared. These compounds have the general formula K[Co(ED3A)X] where Xis Cl-, N02-, or ONO-. The structures of these complexes are inferred from their chemistries and spectral data. The infrared spectra of the compounds have been measured and interpreted. The absorption spectra of the complexes are compared with those for the related series of complexes Co(EDTA)X2-, Co(HEDTA)X-, and Co(MEDTA)X-. The proton nmr spectra indicate that ED3A acts as a pentadentate ligand exhibiting three different AB acetate patterns occurring in the region 4.3 to 3.2 ppm (vs. sodium 3-(trimethylsilyl)-l-propanesulfonate). The spectrum in acid solution confirms the existence of the ED3A ligand by the amine proton absorption and its coupling with the low-field acetate protons. Partial resolution was achieved by use of a cellulose ionexchange column. Numerous examples of cobalt(III) complexes that employ pentadentate chelating agents of the aminopolycarboxylic acid variety have been prepared and are rather well characterized. Schwarzenbach1 prepared the first pentadentate cobalt(III) complexes using ethylenediaminetetraacetic acid. He reported com-(1) G. Schwarzenbach, Helo. Chim. Acta, 32, 839 (1949).pounds of the general formula Co(HY)X-where HY is the singly protonated form of ethylenediaminetetraacetic acid and Xis Brand N02~. Recently Van Saun and Douglas2 have prepared and resolved a series of cobalt(III) complexes of MEDTA, Co(MEDTA)X-, where MEDTA is the anion of N-methylethylenedi-(2) C. W. Van Saun and B. E.
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