Trends in NMR chemical shifts and ligand mobility of TcO(V) and ReO(V) complexes with aminothiols

• Published in: Journal of inorganic biochemistry 2000-04, Vol.79 (1), p.347-351
• Main Authors: Pelecanou, M, Chryssou, K, Stassinopoulou, C.I
• Format: Article
• Language: English
• Subjects: Amines - chemistry; Ligands; Magnetic Resonance Spectroscopy - methods; Models, Molecular; Molecular Conformation; Nuclear magnetic resonance spectroscopy; Organotechnetium Compounds - chemistry; Oxorhenium complexes; Oxotechnetium complexes; Rhenium; Sulfhydryl Compounds - chemistry
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/S0162-0134(99)00227-5

Detailed 1H and 13C NMR studies have been conducted in a series of oxotechnetium and oxorhenium complexes with aminothiol ligands ([SNS][S], [SNN][S], [SNNS]) designed as potential radiopharmaceuticals. The results of these studies in combination with others in the literature show that the oxometal core creates an anisotropic environment and affects the chemical shifts of the coordinated ligand backbone in a consistent way. Protons oriented towards the oxygen appear deshielded relative to their geminals oriented away from the oxygen. In addition, the direction of a side chain (towards or away from the oxometal core) on the ligand backbone is shown to have a major effect on chemical shifts. The fluxional mobility of the ligand in complexes of the [SNS][S] type was also studied by NMR and the free energy of activation Δ G C ≠ for the conformational inversion of the ligand was calculated from the temperature dependence of the carbon chemical shifts. Δ G C ≠ was found to depend on the orientation of the side chain present on the coordinated nitrogen. The energy barrier for the inversion is larger for the oxorhenium complexes than for the analogous oxotechnetium complexes.