Ten-Membered Rings or Lager With One or More Nitrogen Atoms

Transition metal complexes of cyclam with two 2,2,2-trifluoroethylphosphinate pendant arms as probes for 19F magnetic resonance imaging

“…The zwitterionic molecule of H 2 L possesses a centre of symmetry and adopts a “common” angular conformation similar to those found in the crystal structure of the cyclam itself and in its diprotonated forms. 52,53 The phosphinate pendant arms are turned above/below the macrocyclic cavity and stabilize the molecular conformation by strong intramolecular hydrogen bonds [ d (N4#⋯O11) = 2.71 Å, d (N4⋯O12) = 2.85 Å]. Both molecules of the co-crystallized acetic acid are protonated and are bound by very strong hydrogen bonds to the phosphinate oxygen atoms { d (O[AcOH]⋯O11/O12) = 2.58 Å, Fig.…”

“…Further re-crystallization of this material from water afforded (H 4 L )Cl 2 ·4H 2 O which was structurally characterized. In the presence of HCl, all macrocycle amino groups of the ligand molecule are protonated which leads to the conformation (3,4,3,4)-D 52,53 of the cyclam ring. The nitrogen atoms bearing the phosphinate pendant arms form the corners of the (3,4,3,4)-D rectangle (Fig.…”