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Direct 1H NMR assignment of [Co(III)(edta)]−
Communications
853
Polyhedron Vol. 2, No. 8. p, 853, 1983 Rioted
02%5387183
in Great Britain.
Rqcamon
Direct
Department
‘H NMR
S3.00 + .OO Press Ltd.
assignment of [Co(III)(edta)]-
OLIVER W. HOWARTH of Chemistry & Molecular Sciences, University of Warwick, Coventry, CV4 7AL England (Received
12 November 1982; accepted 20 January 1983)
Abstract-Direct assignment of the ‘H NMR spectrum of the ethylenedinitriloNNN’N’-tetraacetate-cobalt(II1) anion [Co(III)(edta)]-, illustrates the value of n.0.e. difference and 2-D n.0.e. spectroscopy in coordination chemistry.
In 1971, Sudmeier et al.’ assigned the ‘H NMR spectrum of aqueous [Co(III)(edta)]Cl on the basis of a theoretical argument concerning the relative rates of deuteriation of the glycinate protons. This assignment has been used as a starting point for many further papers on related compounds[2,3]. We now confirm it directly via the nuclear Overhauser enhancement (n.0.e.) difference spectra[4] shown in the figure. Irradiation of resonance b gives not only the expected enhancement at a but also one at c, and similarly irradiation at e not only affects f but also d. The minor disturbances at other positions arise from imperfect subtraction, and do not integrate significantly. Unfortunately, the selectivity of n.0.e. difference spectroscopy is insufficient to penetrate the crowded region around 6 3.8. However, a 2D-n.0.e. experiment[S] confirms the absence of unreasonable dipolar interactions (such as dfl as well as the presence of the above near-neighbour relationships. The two
h f
d
a
e
methods clearly have considerable coordination chemistry.
value in non-labile
thank the SERC for access to the Bruker WH 400 Spectrometer. Acknowledgement-We
REFERENCES 1. J. L. Sudmeier, A. J. Senzel Inorg. Chem. 1971, 10, 90. 2. 0. W. Howarth, P. Moore Chem. Sot., Dalton Trans., contained therein. 3. 0. W. Howarth, P. Moore Chem. Sot., Dalton
and G. L. Blackmer, and N. Winterton, J. 1974, 2271 and refs and N. Winterton,
J.
Trans. 1975, 360.
4. J. H. Noggle and R. E. Schirmer, The Nuclear Overhauser Efect. Academic, New York (1971). 5. J. Jeener, B. H. Meier, P. Bachmann and R. R. Ernst, J. Chem. Phys. 1979, 71, 4546.
b
_
,
Fig. 1. 400 MHz ‘H NMR spectrum of title compound, labelled according to the half-structure shown. Two ub quartets and one aa’ bb’ near-quartet are resolved. 2. Irradiation of backbone resonance b affects not only a but also c. 3. Irradiation of e affects d as well as f,thus confirming the assignment.
853
Polyhedron Vol. 2, No. 8. p, 853, 1983 Rioted
02%5387183
in Great Britain.
Rqcamon
Direct
Department
‘H NMR
S3.00 + .OO Press Ltd.
assignment of [Co(III)(edta)]-
OLIVER W. HOWARTH of Chemistry & Molecular Sciences, University of Warwick, Coventry, CV4 7AL England (Received
12 November 1982; accepted 20 January 1983)
Abstract-Direct assignment of the ‘H NMR spectrum of the ethylenedinitriloNNN’N’-tetraacetate-cobalt(II1) anion [Co(III)(edta)]-, illustrates the value of n.0.e. difference and 2-D n.0.e. spectroscopy in coordination chemistry.
In 1971, Sudmeier et al.’ assigned the ‘H NMR spectrum of aqueous [Co(III)(edta)]Cl on the basis of a theoretical argument concerning the relative rates of deuteriation of the glycinate protons. This assignment has been used as a starting point for many further papers on related compounds[2,3]. We now confirm it directly via the nuclear Overhauser enhancement (n.0.e.) difference spectra[4] shown in the figure. Irradiation of resonance b gives not only the expected enhancement at a but also one at c, and similarly irradiation at e not only affects f but also d. The minor disturbances at other positions arise from imperfect subtraction, and do not integrate significantly. Unfortunately, the selectivity of n.0.e. difference spectroscopy is insufficient to penetrate the crowded region around 6 3.8. However, a 2D-n.0.e. experiment[S] confirms the absence of unreasonable dipolar interactions (such as dfl as well as the presence of the above near-neighbour relationships. The two
h f
d
a
e
methods clearly have considerable coordination chemistry.
value in non-labile
thank the SERC for access to the Bruker WH 400 Spectrometer. Acknowledgement-We
REFERENCES 1. J. L. Sudmeier, A. J. Senzel Inorg. Chem. 1971, 10, 90. 2. 0. W. Howarth, P. Moore Chem. Sot., Dalton Trans., contained therein. 3. 0. W. Howarth, P. Moore Chem. Sot., Dalton
and G. L. Blackmer, and N. Winterton, J. 1974, 2271 and refs and N. Winterton,
J.
Trans. 1975, 360.
4. J. H. Noggle and R. E. Schirmer, The Nuclear Overhauser Efect. Academic, New York (1971). 5. J. Jeener, B. H. Meier, P. Bachmann and R. R. Ernst, J. Chem. Phys. 1979, 71, 4546.
b
_
,
Fig. 1. 400 MHz ‘H NMR spectrum of title compound, labelled according to the half-structure shown. Two ub quartets and one aa’ bb’ near-quartet are resolved. 2. Irradiation of backbone resonance b affects not only a but also c. 3. Irradiation of e affects d as well as f,thus confirming the assignment.