140-01-2Relevant articles and documents
Spectroscopic Studies of Transition-metal Ion Complexes of Diethylenetriaminepenta-acetic Acid and Diethylenetriaminepenta-methylphosphonic Acid
Oakes, John,Kralingen, Cornelis G. van
, p. 1133 - 1138 (2007/10/02)
The structures of diethylenetriaminepenta-acetate (dtpa) and diethylenetriaminepentamethylphosphonate (dtpmp) complexes of transition-metal ions in aqueous solution have been investigated by n.m.r., e.s.r., and electronic absorption spectroscopy.It is shown that dtpa complexes are much less hydrated than corresponding ethylenediaminetetra-acetate (edta) complexes, consistent with the increase in stability constants.The most marked reduction in water binding on replacing edta by dtpa occurs with Fe3+ and Mn2+ and it is demonstrated using e.s.r. that there is a change in overall stereochemistry from a seven- to a predominantly six-co-ordinate structure for Fe3+.Other dtpa complexes adopt octahedral symmetry as do all the dtpmp complexes.Complexes of dtpmp with Co2+, Ni2+, and , to a lesser extent, Cu2+ have lower hydration numbers than the corresponding ethylenediaminetetramethylphosphonate (edtmp) counterparts, due to simultaneous binding of three nitrogen donors in dtpmp.The III(dtpmp)>7- complex has one bound water similar to III(edtmp)>5-, but the manganese(II) complex of dtpmp is more hydrated than the corresponding edtmp complex.Is is concluded that phosphonate groups produce a less effective crystal field than do carboxyl groups.