A variant of 1,4,7,10-tetraazacyclododecane (cyclen) bearing two semicarbazone pendant groups has been prepared. The octadentate ligand forms complexes with Bi3+ and Pb2+. X-ray crystallography showed that the neutral ligand provides...

A 1,4,7,10-tetraazacyclododecane (cyclen) variant bearing two thiosemicarbazone pendant groups has been prepared. The ligand forms complexes with Mn2+, Co2+ and Zn2+. X-ray crystallography of the Mn2+, Co2+ and Zn2+ complexes showed that the ligand provides a six-coordinate environment for the metal ions. The Mn2+ and Zn2+ complexes exist in the solid state as racemic mixtures of the Δ(δ,δ,δ,δ)/Λ(λ,λ,λ,λ) and Δ(λ,λ,λ,λ)/Λ(δ,δ,δ,δ) diastereomers, and the Co2+ complex exists as the Δ(δ,δ,δ,δ)/Λ(λ,λ,λ,λ) and Δ(λ,λ,λ,δ)/Λ(δ,δ,δ,λ) diastereomers. Density functional theory calculations indicated that the relative energies of the diastereomers are within 10 kJ mol−1. Magnetic susceptibility of the complexes indicated that both the Mn2+ and Co2+ ions are high spin. The ligand was radiolabelled with gallium-68, in the interest of developing new positron emission tomography imaging agents, which produced a single species in high radiochemical purity (>95%) at 90 °C for 10 min.

Hexadentate bis(thiosemicarbazonato)technetium(v) complexes were synthesised, characterised and studied in vivo to demonstrate structural influences on biodistribution.

The positron-emitting radionuclide gallium-68 has become increasingly utilised in both preclinical and clinical settings with positron emission tomography (PET). The synthesis of radiochemically pure gallium-68 radiopharmaceuticals relies on careful consideration of the coordination chemistry. The short half-life of 68 min necessitates rapid quantitative radiolabelling (≤10 min). Desirable radiolabelling conditions include near-neutral pH, ambient temperatures, and low chelator concentrations to achieve the desired apparent molar activity. This review presents a broad overview of the requirements of an efficient bifunctional chelator in relation to the aqueous coordination chemistry of gallium. Developments in bifunctional chelator design and application are then presented and grouped according to eight categories of bifunctional chelator: the macrocyclic chelators DOTA and TACN; the acyclic HBED, pyridinecarboxylates, siderophores, tris(hydroxypyridinones), and DTPA; and the mesocyclic diazepines.

The macrocyclic chelator 1,4,7‐triazacyclononane‐1,4,7‐tri(methylenephosphonic acid) (H6NOTP) has shown significant promise for use in positron emission tomography with the positron‐emitting radionuclide 68Ga3+. We report the X‐ray crystal structure of the neutral complex 1,4,7‐triazacyclononane‐1,4,7‐tri(methylenephosphonato)gallium(III) ([Ga(H3NOTP)]), which crystallised in the centrosymmetric space group P21/n. The coordination geometry of the Ga3+ ion is distorted octahedral with three macrocyclic amine N donor atoms and three singly deprotonated phosphonato O donor atoms. Two discrete enantiomers, Δ(λλλ)‐SSS and Λ(δδδ)‐RRR, are present as a racemate within the unit cell. Intermolecular hydrogen bonds between phosphonic acid groups of adjacent complexes form a two‐dimensional sheet network. Density functional theory (DFT) calculations supported the observation of complexes with low electric field gradient values with slight but significant deviations from ideal octahedral geometry. The DFT calculations were also used to investigate the influence of intermolecular interactions and ligand protonation states on the coordination environment and surface charge distribution.