Synthesis and characterization of the yttrium(III) and lutetium(III) complexes of 1,4,7-tris(carbamoylmethyl)-1,4,7-triazacyclononane (TCMT). Crystal structure of [Y(TCMT)(CF₃SO₃)₂(H₂O)](CF ₃SO₃)

The 1,4,7-tris(carbamoylmethyl)-1,4,7-triazacyclononane (TCMT) ligand and its complexes with yttrium(III) and lutetium(III) have been prepared. [Y(TCMT)(CF₃SO₃)₂(H₂O)](CF ₃SO₃) crystallizes in the centrosymmetric triclinic space group P1 (No. 2) with a = 10.3660(14), b = 11.7663(15), c= 13.3008(20) Å, a = 72.079(10), ß = 81.684(12), γ = 78.401(11)°, V= 1506.1(4) and Z = 2. The structure was refined to R = 5.64% for those 1758 reflections with |F_o| > 6σ(|F_o|). The nonacoordinate yttrium(III) ion has a bound water molecule, two bound triflate ions and a hexadentate TCMT ligand. The coordination geometry may be described as a 3:5:1 arrangement in which the C₆N₃ backbone occupies the '3' sites and H₂O the unique '1' site, or alternatively as a capped square antiprism or as a distorted tricapped trigonal prism. The [Ln(TCMT)]³⁺ complexes dissociate completely in aqueous solution within 25 min at pH 6.0 and 37°C in the presence of Cu²⁺ as a trapping agent. Molecular mechanics calculations have been used to investigate the strain energy of the TCMT and 1,4,7-triazacyclononane-1,4,7-triacetate (NOTA) ligands in complexes that are 6-, 7-or 9-coordinate.