title: Syntheses and characterization of dicarbonyl-nitrosyl complexes of technetium(I) and rhenium(I) in aqueous media: spectroscopic, structural, and DFT analyses.
abstract: This work describes new synthetic routes to produce mixed carbonyl-nitrosyl complexes of technetium(I) and rhenium(I) in aqueous media. NaNO2, NOHSO4, and NO2(g) have been used to produce in situ nitrous acid as the primary source of NO+. Starting from the organometallic precursor fac-[MX3(CO)3]+, 1 (M = 99Tc, Re; X = Cl, Br), the formation of mixed dicarbonyl-mononitrosyl complexes was observed in aqueous hydrochloric and hydrobromic acid. Time-dependent analyses of the reactions by means of HATR-IR and 99Tc NMR spectroscopy in solution revealed the almost quantitative substitution of one CO ligand by NO+ and, thus, the formation of complexes with facial arrangement of the three pi-acceptor ligands. In the case of technetium, the monomeric complex (NEt4)[TcCl3(CO)2NO] (3a) and the dimeric, chloride-bridged, neutral complex [TcCl(mu-Cl)(CO)2NO]2 (4a) were produced. In the case of rhenium, the monomeric species (NEt4)[ReBr2X(CO)2NO] (X = Br (3b), NO3 (5)) was solely isolated. The X-ray structure of complexes 4a and 5 are discussed. The crystallographic analyses revealed the coordination of the NO+ group trans to the terminal chloride (4a) or the bromide (5), respectively. Crystal data: complex 4a (C4Cl4N2O(6)Tc2), monoclinic, Cc, a = 18.82(3) A, b = 6.103(6) A, c = 12.15(2) A, alpha = 90 degrees , beta = 105.8(2) degrees , gamma = 90 degrees , V = 1343(3) A(3), Z = 4; complex 5 (C10H20N3O(6)Br2Re), orthorhombic, P2(1)2(1)2(1), a = 10.2054(5) A, b = 12.5317(7) A, c = 13.9781(7) A, V = 1787.67(16) A(3), Z = 4. The isolated complexes and their potential facial isomers have been further investigated by density functional theory (DFT) calculations. The energy differences of the isomers are relatively small; however, the calculated energies are consistent with the formation of the observed and isolated compounds. The calculated bond lengths and angles of complex 5 are in good agreement with the data determined by X-ray diffraction. Experiments on the no-carrier-added level starting from fac-[99mTc(H2O)3(CO)3]+ revealed the formation of the complex fac-[99mTcCl(H2O)2(CO)2NO]+ in reasonable good yields. This aqueous-based, synthetic approach will enable the future evaluation of this novel, low-valent metal precursor for potential use in radiopharmacy.
authors.affiliation: Center for Radiopharmaceutical Science, ETH-PSI-USZ, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland. roger.schibli@psi.ch
authors.forename: Roger
authors.initials: R
authors.lastname: Schibli
authors.forename: Niklaus
authors.initials: N
authors.lastname: Marti
authors.forename: Patrick
authors.initials: P
authors.lastname: Maurer
authors.forename: Bernhard
authors.initials: B
authors.lastname: Spingler
authors.forename: Marie-Line
authors.initials: ML
authors.lastname: Lehaire
authors.forename: Volker
authors.initials: V
authors.lastname: Gramlich
authors.forename: Charles L
authors.initials: CL
authors.lastname: Barnes
mesh_terms: D000465:Algorithms; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*; D013667:Technetium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D014867:Water; D012211:Rhenium; D013667:Technetium