1,4,7-Triazacyclononane-1,4,7-triyltrimethylenetris-(phenylphosphinate) enforces octahedral geometry: crystal and solution structures of its metal complexes and comparative biodistribution studies of radiolabelled indium and gallium complexes

1,4,7-Triazacyclononane-1,4,7-triyltrimethylenetris(phenylphosphinate) formed C₃-symmetric complexes with the divalent ions of Co, Ni, Cu and Zn and structurally similar complexes with the trivalent ions of Fe, Co, Ga and In. For each of the eight crystal structures examined, the ligand adopts the same rigid conformation and a single chiral diastereoisomer is formed (RRR or SSS at each stereogenic phosphorus centre). The geometry around the metal centre is slightly distorted octahedral. The copper(II) complex only undergoes a Jahn-Teller distortion below 100 K, and the pink cobalt(II) complex only slowly oxidises to the dark blue cobalt(III) complex. The chiral gallium(III) complex may be resolved by preparative HPLC, and its ¹H NMR spectrum has been fully assigned with the aid of two-dimensional methods. The indium-111 and gallium-67 complexes have been examined in vivo and exhibit selective biliary clearance associated with their lipophilic nature.