To explore structural differences in In3+, Y3+, and Lu3+ chelates, we prepared M(DTPA-BA(2)) complexes (M = In, Y, and Lu; DTPA-BA(2) = N,N"-bis(benzylcarbamoylmethyl)diethylenetriamine-N,N',N"-triacetic acid) by reacting the trisodium salt of DTPA-BA(2) with 1 equiv of metal chloride or nitrate. All three complexes have been characterized by elemental analysis, HPLC, IR, ES-MS, and NMR (H-1 and C-13) methods. ES-MS spectral and elemental analysis data are consistent with the proposed formula for M(DTPA-BA(2)) (M = In, Y, and Lu) and have been confirmed by the X-ray crystal structures of both In(DTPA-BA(2)).2H(2)O and Y(DTPA-BA(2))(CH3OH) complexes. By a reversed-phase HPLC method, it was found that In(DTPA-BA(2)) is more hydrophilic than M(DTPA-BA(2)) (M = Y and Lu), most likely due to the dissociation of the two carbonyl oxygen donors in solution. The X-ray crystal structure of In(DTPA-BA(2)) revealed a rare example of an eight-coordinated In3+ complex with DTPA-BA(2) bonding to the In3+ in a distorted square antiprism coordination geometry. Both benzylamine groups are in the trans position relative to the acetate-chelating arm that is attached to the central N atom. The Y3+ in Y(DTPA-BA(2))(CH3OH) is nine-coordinated with an octadentate DTPA-BA(2) and a methanol oxygen. The coordination geometry is best described as a tricapped trigonal prism. One benzylamine group is trans and the other cis to the acetate-chelating arm that is attached to the central N atom. All three M(DTPA-BA(2)) Complexes (M = In, Y, and Lu) exist as at least three isomers in solution (similar to10 mM), as shown by the presence of 6-8 overlapped H-1 NMR signals from the methylene hydrogens of the benzylamine groups. The coordinated DTPA-BA(2) remains rigid even at temperatures >85degreesC. The exchange rate between different isomers in M(DTPA-BA(2)) (M = In, Y, and Lu) is relatively slow at high concentrations (>1.0 mM), but it is fast due to the partial dissociation and rapid interconversion of different isomers at lower concentrations (similar to10 muM). It is not surprising that M(DTPA-BA(2)) complexes (M = In, Y, and Lu) appear as a single peak in their respective HPLC chromatogram.