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/sup 13/C NMR study of (meso-2,3-butanediaminetetraacetato)nickelate(II)

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic00264a028· OSTI ID:5522795
The temperature and pH dependences of the /sup 13/C NMR spectrum of the paramagnetic nickel(II) complex with meso-2,3-butanediaminetetraacetic acid are reported and interpreted to indicate that the ligand acts as a hexadentate coordinator at all temperatures accessible in deuteriated water and over the pH range from 1 to 13. Less than 1% of the ligands act as pentadentate coordinators. The incomplete coalescence of acetate resonances coupled with concurrent complete coalescence of backbone resonances is interpreted to indicate that ..delta.. reversible lambda conversion proceeds rapidly at moderate (ca 70/sup 0/C) temperatures through a symmetrical intermediate formed without bond breaking, while nitrogen inversion, which requires nickel-nitrogen bond rupture, is slow over the accessible temperature range (<109 /sup 0/C). The previously proposed mechanism for the racemization of Ni(EDTA)/sup 2 -/, which required the presence of an uncoordinated ligand arm, is probably incorrect. A mechanism is proposed that explains the previous and current data without invoking action by a free acetate arm. The meso-BDTA chelate ring is found to be more puckered than the chelate ring of EDTA. The pentadentate form of meso-BDTA is destabilized by at least 8 kJ mol/sup -1/ relative to the pentadentate form of EDTA because of steric interaction between a free carboxylate and the axial methyl substituent. 21 references, 4 figures, 1 table.
Research Organization:
Univ. of New Orleans, LA
OSTI ID:
5522795
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 26:17; ISSN INOCA
Country of Publication:
United States
Language:
English