fac - 99m Tc/Re-tricarbonyl complexes with tridentate aminocarboxyphosphonate ligands: suitability of the phosphonate group in chelate ligand design of new imaging agents.

•Aminocarboxyphosphonates chelate tridentately to fac-[99mTc/Re(CO)3]+ cores.•X-ray/NMR/HPLC data unambiguously establish phosphonate binding to the cores.•Some chelates form linkage isomers that interconvert in a pH-dependent ratio.•Isomers with phosphonate binding are favored over carboxylate binding at pH > 6.•Phosphonate-to-fac-[99mTc(CO)3]+ binding is totally robust in in vivo rat studies.