acid residue or the residue of another compound capable of forming an amide or ester linkage with two or more chelant moieties (with any substitutent preferably being chosen to enhance solubility or biodistribution of the resultant compound, such as --OH, --NH2 or --CO2 H, a peptide residue, a polypeptide or protein such as a plasma protein, antibody or antigen, or other suitable moiety).