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Novel Oxorhenium and Oxotechnetium Complexes from an Aminothiol[NS]/Thiol[S] Mixed‐Ligand System
Author(s) -
Bouziotis Penelope,
Pirmettis Ioannis,
Pelecanou Maria,
Raptopoulou Catherine P.,
Terzis Aris,
Papadopoulos Minas,
Chiotellis Efstratios
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010903)7:17<3671::aid-chem3671>3.0.co;2-l
Subject(s) - denticity , ligand (biochemistry) , chemistry , rhenium , deprotonation , protonation , square pyramidal molecular geometry , crystallography , thiol , stereochemistry , molecule , crystal structure , inorganic chemistry , receptor , ion , biochemistry , organic chemistry
The simultaneous action of a bidentate aminothiol ligand, L n H, ( n =1: (CH 3 CH 2 ) 2 NCH 2 CH 2 SH and n =2: C 5 H 10 NCH 2 CH 2 SH) and a monodentate thiol ligand, LH (LH: p ‐methoxythiophenol) on a suitable MO (M=Re, 99g Tc) precursor results in the formation of complexes of the general formula [MO(L n )(L) 3 ] ( 1, 2 for Re and 5, 6 for 99g Tc). In solution these complexes gradually transform to [MO(L n )(L) 2 ] complexes ( 3, 4 for Re and 7, 8 for 99g Tc). The transformation is much faster for oxotechnetium than for oxorhenium complexes. Complexes 1 – 4, 7 , and 8 have been isolated and fully characterized by elemental analysis and spectroscopic methods. Detailed NMR assignments were made for complexes 3, 4, 7 , and 8 . X‐ray studies have demonstrated that the coordination geometry around rhenium in complex 1 is square pyramidal ( τ =0.06), with four sulfur atoms (one from the L 1 H ligand and three from three molecules of p ‐methoxythiophenol) in the basal plane and the oxo group in the apical position. The L 1 H ligand acts as a monodentate ligand with the nitrogen atom being protonated and hydrogen bonded to the oxo group. The four thiols are deprotonated during complexation resulting in a complex with an overall charge of zero. The coordination geometry around rhenium in complex 4 is trigonally distorted square pyramidal ( τ =0.41), while in the oxotechnetium complex 7 it is square pyramidal ( τ =0.16). In both complexes L n H acts as a bidentate ligand. The NS donor atom set of the bidentate ligand and the two sulfur atoms of the two monodentate thiols define the basal plane, while the oxygen atom occupies the apical position. At the technetium tracer level ( 99m Tc), both types of complexes, [ 99m TcO(L n )(L) 3 ] and [ 99m TcO(L n )(L) 2 ], are formed as indicated by HPLC. At high ligand concentrations the major complex is [ 99m TcO(L n )(L) 3 ], while at low concentrations the predominant complex is [ 99m TcO(L n )(L) 2 ]. The complexes [ 99m TcO(L n )(L) 3 ] transform to the stable complexes [ 99m TcO(L n )(L) 2 ]. This transformation is much faster in the absence of ligands. The complexes [ 99m TcO(L n )(L) 2 ] are stable, neutral, and also the predominant product of the reaction when low concentrations of ligands are used, a fact that is very important from the radiopharmaceutical point of view.