Synthesis,characterization and structure of oxorhenium(V) complexes with 2-methylmercaptobenzamide

The neutral, mononuclear complex [ReO(mta)₂Cl] (1) [Hmta?=?2-(methylmercapto)aniline] was prepared by reaction of trans-[ReOCl₃(PPh₃)₂] with a twofold molar excess of Hmta in methanol. The oxo-bridged dimer (μ-O)[ReO(mta)₂]₂ (2) was synthesized by reacting [ReOCl₃(PPh₃)₂] with a twofold excess of Hmta in a 9?:?1 acetone/water mixture. The compounds were characterized by spectroscopy and complex 1 also by X-ray crystallography. Complex 1 has a distorted octahedral geometry with the chloride coordinated trans to the oxo group, and with the chelating ligands in the equatorial plane in a cis-N cis-S configuration.     

Synthesis, characterization, and stereochemistry of oxorhenium(V) complexes with 2-aminoethanethiolate

A series of oxorhenium(V) complexes with 2-aminoethanethiolate (aet), [ReO(aet-N,S)(D-pen-N,O,S)] (2), [[ReO(aet-N,S)(2)](2)O] (3), [ReO(Cl)(aet-N,S)(2)] (4), and [ReO(aet-N,S)(Haet-S)(2)]Cl(2) ([5]Cl(2)) was newly prepared starting from ReO(4)(-). The reaction of NH(4)ReO(4) with a 1:1 mixture of Haet.HCl and D-H(2)pen (D-penicillamine) in the presence of SnCl(2).2H(2)O in water gave 2, 3, and the known complex [ReO(D-Hpen-N,S)(D-pen-N,O,S)] (1). These complexes were fractionally precipitated by controlling the pH of the reaction solution. The complex 2 was also prepared in a higher yield by a similar reaction using methanol as a solvent. The crystal structure of 2 was determined by X-ray crystallography; 2 crystallizes in the tetragonal space group P4(3) with a = 9.621(1), c = 12.911(1) A, V = 1195.0(3) A(3), and Z = 4. The oxorhenium(V) core in 2 is coordinated by a bidentate-N,S aet ligand and a tridentate-N,O,S D-pen ligand, having a distorted octahedral geometry with a cis-N cis-S configuration in the equatorial plane perpendicular to the O-Re-O axis. The 1:2 reaction of NH(4)ReO(4) with Haet.HCl in the presence of SnCl(2).2H(2)O in methanol produced 4, which is interconvertible with 3, while the corresponding 1:3 reaction resulted in the isolation of [5]Cl(2). The complexes 4 and 5 were also structurally characterized; 4 crystallizes in the monoclinic space group P2(1)/c with a = 6.839(1), b = 10.0704(6), c = 14.1075(8) A, beta = 91.729(8) degrees, V = 971.2(2) A(3), and Z = 4, while [5]Cl(2) crystallizes in the triclinic space group P1 with a = 11.938(3), b = 12.366(3), c = 5.819(1) A, alpha = 102.71(2), beta = 101.28(2), gamma = 75.41(2) degrees, V = 802.0(3) A(3), and Z = 2. In 4, the oxorhenium(V) core is octahedrally coordinated by two bidentate-N,S aet ligands, which form a cis-N cis-S configurational equatorial plane with a Cl(-) ion trans to the oxo ligand. On the other hand, the oxorhenium(V) core in [5](2+) is coordinated by one bidenate-N,S aet and two monodentate-S Haet ligands, having a distorted trigonal-bipyramidal geometry with S and N donors at the apical positions.     

Luminescent square-planar platinum(II) complexes with tridentate 3-bis(2-pyridylimino)isoindoline and monodentate N-heterocyclic ligands

A series of platinum(II) complexes with 1,3-bis(2-pyridylimino)isoindoline (BPI) derivatives were prepared by substitution of the coordinated Cl in the precursor complex Pt(BPI)Cl with a N-heterocyclic ligand such as pyridine, phthalazine or phenanthridine. These complexes display orange to red luminescence in fluid dichloromethane solutions and in the solid states at room temperature. The photophysical properties were tuned by introducing electron-withdrawing -NO(2) or electron-donating -NH(2) to the BPI ligand. The DFT computational studies suggest that the emission in the N-heterocyclic ligand substituted platinum(II) complexes originates mainly from the (3)[π→π*(BPI)] (3)IL triplet excited state, mixed with some (3)[dπ(Pt)→π*(BPI)] (3)MLCT character. Compared with the precursor Pt(BPI)Cl, both the low-energy absorption and the emission in the N-heterocyclic ligand substituted platinum(II) complexes exhibits a distinct blue-shift due to an obviously enhanced contribution from the (3)IL state and a reduced (3)MLCT character.     

Different coordination modes of tetradentate Schiff bases in monomeric and dimeric oxorhenium(V) complexes

The reactions of the tetradentate amine-phenol type Schiff bases H₂sal₂en (1,2-ethylenebis(salicylideneimine) and H₂sal₂mp (1,2-benzylenebis(salicylideneimine)) with trans-[ReOCl₃(PPh₃)₂] or (n-Bu₄N)[ReOCl₄] in air gave the products (µ-O)[ReO(sal₂en)]₂ (1) and [ReOCl(sal₂mp)] (2), respectively. X-ray and spectroscopic studies have shown that 1 contains the linear O=Re–O–Re=O grouping, with the four donor atoms of sal₂en^2? coordinating in the square plane cis to the oxo ions. In 2, a cis oxo-chloro arrangement is observed with a phenolic oxygen being coordinated trans to the oxo group. The terminal Re=O bond lengths in 1 and 2 are 1.709(4) and 1.683(3)?Å, respectively.     

New [Mo(eta3-allyl)(CO)2L3]+ complexes with monodentate or tridentate nitrogen-donor ligands

Cationic complexes [Mo(eta(3)-allyl)(CO)2L3]+ (L3 = either nitrogen-donor tridentate ligand or three monodentate ligands) were prepared in high yield and under mild conditions using as precursors either the triflato complex [Mo(eta(3)-allyl)(OTf)(CO)2(NCMe)2] or the combination of the chloro complex [Mo(eta(3)-allyl)Cl(CO)2(NCMe)2] and the salt NaBAr'(4)(Ar'= 3,5-bis(trifluoromethyl)phenyl). The tridentate ligands employed were 2,2':6',2'-terpyridine (terpy) and cis,cis-1,3,5-cyclohexanetriamine (CHTA), whereas the monodentate ligands imidazole (im) and 3,5-dimethylpyrazole (dmpz) were chosen. In order to stabilize the labile intermediates, an excess of acetonitrile was used in most of the syntheses. However, the pyrazole complex was prepared through a nitrile-free route to avoid reactions at the coordinated nitrile. The solid state structures of [Mo(eta(3)-methallyl)(CO)2(terpy)]OTf (2), [Mo(eta(3)-methallyl)(CO)2(CHTA)]BAr'4 (3), [Mo(eta(3)-methallyl)(CO)2(NCMe)3]BAr'4 (4), [Mo(eta(3)-allyl)(CO)2(im)3]OTf (5) and [Mo(eta(3)-allyl)(CO)2(dmpz)3]BAr'4 (6) were determined by means of single-crystal X-ray diffraction.     

Synthesis and structural characterization of cationic octahedral oxorhenium(V) complexes with bidentate imidazole derivatives

Cationic distorted octahedral complexes [ReOCl(OEt)(L)(PPh₃)]X {L = 2-(1-ethylaminomethyl)-1-methylimidazole (eami), 2-(1-methylaminomethyl)-1-methylimidazole (mami), 2-(1-ethylthiomethyl)-1-methylimidazole (etmi); X=ReO₄, PF₆} were prepared by reaction of trans-[ReOCl₃(PPh₃)₂] with a twofold molar excess of L in ethanol under anaerobic conditions. X-ray structure determinations of [ReOCl(OEt)(eami)(PPh₃)](ReO₄) (1a) and its etmi equivalent (3a) were performed. In 1a coordination of the chloride occurs trans to the imidazole nitrogen. However, in 3a the chloride is coordinated trans to the ethereal sulfur donor of etmi.     

Synthesis,structure, protein binding,and cytotoxicity of zinc(II) complexes with tridentate NNO Schiff-base ligands

Mononuclear and trinuclear zinc(II) complexes (1 and 2) with tridentate NNO Schiff-base ligands (HL¹?=?N-2-pyridiylmethylidene-4-chloro-2-hydroxy-phenylamine, HL²?=?N-2-pyridiylmethylidene-2-hydroxy-5-chloro-phenylamine) have been synthesized and characterized by single-crystal X-ray diffraction and elemental analysis. The binding properties of zinc(II) complexes with calf thymus DNA (CT-DNA) and HSA were investigated by UV–visible, fluorescence, and circular dichroism spectra. The zinc(II) complexes bind significantly to CT-DNA by intercalation and bind to protein HSA through a static quenching mechanism. The in vitro cytotoxicity of the complexes on human tumor cells lines was assessed by 3-(4,5-dimathylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide, Hoechst 33258 staining experiments.     

Oxovanadium(V) complexes incorporating tridentate aroylhydrazoneoximes: Synthesis, characterizations and antibacterial activity

Some new oxovanadium(V) complexes, [VOL^1-3(OEt)(EtOH)] (1-3), have been reported, which were obtained from the reaction of the Schiff bases H₂L^1-3 (where H₂L¹ = the salicylhydrazone of diacetyl monoxime; H₂L² = the 4-methoxy salicylhydrazone of diacetyl monoxime and H₂L³ = the 4-hydroxy salicylhydrazone of diacetyl monoxime) with VO(acac)₂ in a 1:1 molar ratio. Three 4-R-aroylhydrazoneoximes (V) have been used as ligands in the present study, differing in the inductive effect of the substituent R (R = H, OCH₃ and OH), in order to observe their influence, if any, on the redox potentials and biological activity of the complexes. All the synthesized ligands and metal complexes were successfully characterized by elemental analysis, IR, UV-Vis and NMR spectroscopy. An X-ray diffraction study of [VOL¹(OEt)(EtOH)] (1) reveals that the metal center has a distorted octahedral O₅N coordination sphere, where the O,N,O donor ligand and the ethoxo group constitute a satisfactory O₃N basal plane. Cyclic voltammetry of the complexes show a quasi-reversible cyclic voltammetric response in the potential range 0.29-0.36 V involving a single electron V(V)-V(IV) reduction. The complexes have also been screened for their antibacterial activity against Escherichia coli, Bacillus, Proteus and Klebsiella. Minimum inhibitory concentrations of these complexes and the antibacterial activities indicate compound 1 as the potential lead molecule for drug design.     

Synthesis and characterization of oxorhenium(v) diamido pyridine complexes that catalyze oxygen atom transfer reactions

The detailed syntheses of complexes 1-4, Re(O)(X)(DAP) (X = Me, 1; Cl, 2; I, 3; OTf (triflate), 4) incorporating the diamido pyridine (DAP) ancillary ligand (2,6-bis((mesitylamino)methyl)pyridine) are described and shown to be effective catalysts for oxygen atom transfer (OAT) reactions of PyO to PPh(3). The catalytic activities are as follows: 4≈3 > 2 > 1. The observed electronic trend is consistent with the turnover limiting reduction of the proposed Re(VII) dioxo intermediate, Re(O)(2)(X)(DAP), during the catalytic cycle. The catalytic activity of complexes 1-3 was compared to previously published diamido amine (DAAm) oxorhenium complexes of the type Re(O)(X)(DAAm) (X = Me, 5; Cl, 6; I, 7 and DAAm = N,N-bis(2-arylaminoethyl)methylamine) which exhibit hydrolytic degradation during the catalytic reaction. Complexes 1-3 displayed higher turnover frequencies compared to 5-7. This higher catalytic activity was attributed to the more rigid DAP ligand backbone, which makes the complexes less susceptible to decomposition. However, another decomposition pathway was proposed for this catalytic system due to the observation of Re(O)(3)((MesNCH(2))(MesNCH)NC(5)H(3)) 8 in which one arm of the DAP ligand is oxidized.     

Synthesis and characterization of six-coordinate "3 + 2" mixed-ligand oxorhenium complexes with the o-diphenylphosphinophenolato ligand and tridentate coligands of different N and S donor atom combinations

A series of octahedral six-coordinate oxorhenium(V) mixed ligand complexes containing the common [ReO(L)]2+ fragment (L = o-OC6H4P(C6H5)2] have been synthesized and characterized. Hence, it was shown that the [ReO(L)]2+ moiety can accommodate a variety of tridentate ligands containing a central amine group amenable to deprotonation and different combinations of lateral groups, such as ethylamine, substituted ethylamine, ethylthiol, and ethylthioether arms. In particular, by reaction of equimolar amounts of the pertinent HLn ligands with the [(n-C4H9)4N][ReOCl3(L)] precursor in refluxing acetonitrile/methanol or dichloromethane/methanol mixtures, the following series of [ReO(Ln)(L)]+/0 oxorhenium(V) complexes has been generated: ReO[[N(CH2CH2NH2)2][o-OC6H4P(C6H5)2]]Cl (1); ReO[[C2H5)2NCH2CH2NCH2CH2S][o-OC6H4P5)2]] (2); ReO[[(CH2)4NCH2CH2NCH2CH2S][o-OC6H4P(C6H4P(C6H5)2]] (3); and ReO[[C2H5SCH2CH2NCH2CH2S][o-OC6H4P(C6H5)2]] (4). The complexes are closed-shell 18-electron oxorhenium species, which adopt octahedral geometries both in solution and in the solid state, as established by conventional physicochemical techniques including multinuclear NMR and single-crystal X-ray diffraction analyses.     

Monooxorhenium(V) complexes with the tridentate Schiff baseN-(2-hydroxyphenyl)salicylideneimine

Summary The reactions of the tridentate Schiff base ligandN-(2-hydroxyphenyl) salicylideneimine (HOPhsalH) with oxotetrachlororhenate (IV) have been investigated. The complexes (Bu₄N)[ReOCl₃(HOPhsal)], (Bu₄N)[ReOCl₂(OPhsal)],cis- [ReOCl(MeOH)(OPhsal)],trans-[ReOCl(MeOH)(OPhsal)] (1), trans-[ReOCl(OH₂)(OPhsal)] · Et₂O (2), trans-[ReOCl(OH₂)(OPhsal)] · Me₂CO,cis-[ReOCl(PPh₃)(OPhsal)],cis-[ReOCl(PMe₂Ph)(OPhsal)](3) have been synthesized and characterized. The crystal structures of(1), (2) and(3) have been solved from three-dimensional x-ray data by Patterson and Fourier methods and refined by least-squares methods to R 0.10 for(1), 0.042 for(2) and 0.059 for(3). In all the three complexes, the ligands surrounding the rhenium atom are at the apices of a distorted octahedron, with the equatorial ONO donor atoms of the tridentate Schiff base bent away from the O_oxo and toward the loosely bound MeOH in(1), H₂O in(2) and Cl in(t3). The fourth equatorial substituent is Cl (1 and2) and PMe₂Ph(3) and the rhenium atoms lie 0.30–0.37 Å above the best plane through the four equatorial atoms, in the direction of the O_oxo. All interatomic distances and angles are normal.     

Synthesis and coordination behavior of Cu(I) bis(phosphaethenyl)pyridine complexes

Cu(I) complexes bearing BPEP as a PNP-pincer type phosphaalkene ligand undergo effective bonding interactions with SbF(6)(-) and PF(6)(-) as non-coordinating anions to give [Cu(SbF(6))(BPEP)] and [Cu(2)(BPEP)(2)(μ-PF(6))](+), respectively [BPEP = 2,6-bis(1-phenyl-2-phosphaethenyl)pyridine]. NMR and theoretical studies indicate a reduced anionic charge of the μ-PF(6) ligand, which is induced by the strong π-accepting ability of BPEP.     

Synthesis,crystal structures,and biological activity of oxovanadium(V) complexes with similar tridentate hydrazone ligands

Two new oxovanadium(V) complexes, [VOL¹(OEt)(EtOH)] (1) and [VOL²(OMe)(MeOH)] (2), were prepared by reaction of [VO(acac)₂] (where acac?=?acetylacetonate) with N′-(3-bromo-2-hydroxybenzylidene)-4-methylbenzohydrazide (H₂L¹) in ethanol and N′-(3-bromo-2-hydroxybenzylidene)-4-methoxybenzohydrazide (H₂L²) in methanol, respectively. Crystal and molecular structures of the complexes were determined by elemental analysis, infrared spectra, and single-crystal X-ray diffraction. The V ions have octahedral coordination. Thermal stability and the inhibition of urease of the complexes were studied.     

Synthesis,crystal structures,and catalytic properties of two oxidovanadium(V) complexes with tridentate Schiff bases

Two new oxidovanadium(V) complexes, [VO₂L¹] (I) and [VO₂L²] (II), where L¹ and L² are the deprotonated forms of 4-methyl-2-[(2-morpholin-4-ylethylimino)methyl]phenol (HL¹) and 2-[(2-isopropylaminoethylimino) methyl]-4-trifluoromethoxyphenol (HL²), respectively, have been prepared and characterized by physico chemical methods and single crystal X-ray diffraction (CIF files CCDC nos. 1443671 (I), 1443672 (II)). The V atom in each complex is coordinated by the phenolate oxygen, imino nitrogen and amino nitrogen of the Schiff base ligand, and two oxo groups, forming trigonal-bipyramidal geometry. The oxidation of olefins with the complexes as catalyst was evaluated, which indicated that both complexes showed effective catalytic efficiency in oxidation of several aliphatic and aromatic substrates by using tert-butyl hydrogen peroxide as oxidant.     

Heterofunctionalized phosphines derived from (2-formylphenyl)diphenylphosphine and their reactions with oxorhenium(V) complexes

Reactions of [ReOCl₃(PPh₃)₂] with a potentially tridentate Schiff base derived from (2-formylphenyl)diphenylphosphine and 2-aminophenol, HL¹P, (HL¹P = Ph₂PC₆H₄-2-HCN(C₆H₄-2-OH)) result in a rapid decomposition of the Schiff base and the formation of a large number of hitherto non-identified metal-containing species, while from similar reactions with the analogoue phosphine oxide HL¹PO, (HL¹PO = Ph₂P(O)C₆H₄-2-HCN(C₆H₄-2-OH)) products of the compositions [ReOCl₂(PPh₃)(L¹PO)] (1) and [Re(NC₆H₄-2-OH)Cl₃(PPh₃)₂] (2) could be isolated. The structure of 2 is an experimental proof of the preceding, metal-induced cleavage of the C–N double bond. A subsequent reaction of the released 2-aminophenol forms the final phenylimido ligand.Reduction of HL¹P with NaBH₄ gives the phosphine amine H₂L²P (H₂L² = Ph₂P(C₆H₄-2-CH₂NH(C₆H₄-2-OH))) in good yield. Reactions of H₂L²P with common oxorhenium(V) complexes result in the formation of the stable rhenium(V) complex [ReOCl₂(HL²P)] (3) with a facially coordinated HL²P^? ligand.     

Syntheses and oxidation of methyloxorhenium(V) complexes with tridentate ligands

Four new methyloxorhenium(V) compounds were synthesized with these tridentate chelating ligands: 2-mercaptoethyl sulfide (abbreviated HSSSH), 2-mercaptoethyl ether (HSOSH), thioldiglycolic acid (HOSOH), and 2-(salicylideneamino)benzoic acid (HONOH). Their reactions with MeReO(3) under suitable conditions led to these products: MeReO(SSS), 1, MeReO(SOS), 2, MeReO(OSO)(PAr(3)), 3, and MeReO(ONO)(PPh(3)), 4. These compounds were characterized spectroscopically and crystallographically. Compounds 1 and 2 have a five-coordinate distorted square pyramidal geometry about rhenium, whereas 3 and 4 are six-coordinate compounds with distorted octahedral structures. The kinetics of oxidation of 2 and 3 in chloroform with pyridine N-oxides follow different patterns. The oxidation of 2 shows first-order dependences on the concentrations of 2 and the ring-substituted pyridine N-oxide. The Hammett analysis of the rate constants gives a remarkably large and negative reaction constant, rho = -4.6. The rate of oxidation of 3 does not depend on the concentration or the identity of the pyridine N-oxide, but it is directly proportional to the concentration of water, both an accidental and then a deliberate cosolvent. The mechanistic differences have been interpreted as reflecting the different steric demands of five- and six-coordinate rhenium compounds.     

Rhenium complexes with 2-(diphenylphosphinomethyl)aniline: formation of a cyclic, trinuclear oxorhenium(V) core

Reactions of 2-(diphenylphosphinomethyl)aniline, H(2)L(2), with (NBu(4))[ReOCl(4)] yield different oxo rhenium(V) complexes depending on the conditions applied. This comprises monomeric compounds such as [ReOCl(3)(H(2)L(2))] (1), [ReOCl(2)(OMe)(H(2)L(2))] (2), or [ReO(2)(H(2)L(2))(2)]Cl (5) as well as the dimeric μ-oxo complex [{ReOCl(2)(H(2)L(2))}(2)]O] (3) and the oxo-bridged trimer [{ReOCl(H(2)L(2))}O](3) (4). The latter compound represents the first example of a hitherto unknown trinuclear, cyclic oxo(V) core. [{ReOCl(H(2)L(2))}O](3) contains a tensed 6-membered metallacycle, which readily undergoes rearrangements and reactions with additional ligands. Compounds of the compositions 5 and [ReO(2)(H(2)L(2))(H(2)L(1))]Cl (6) were isolated either from the decomposition of 4 in CH(2)Cl(2)/n-pentane or from reactions with 2-(diphenylphosphino)aniline, H(2)L(1).     

A density functional study of oxorhenium(V) complexes incorporating quinoline or isoquinoline carboxylic acids: structural,spectroscopic, and electronic properties

Density functional theory calculations have been performed for understanding factors responsible for the different stabilities of particular isomers of [ReOX(N–O)₂], where N–O represents carboxylate ligand chelating to the oxorhenium core through N and O atoms. DFT/B3LYP calculations have been carried out for all possible potential isomers of [ReO(OMe)(2-qc)₂] (1), [ReOCl(2-qc)₂] (2), [ReO(OMe)(1-iqc)₂] (3), and [ReOCl(1-iqc)₂] (4). Interestingly, complex 1 shows a very rare example of trans [O=Re–OMe] conformation with two chelating N,O-donor ligands in the equatorial plane, whereas the others were found to be the most common structure of [ReOX(N–O)₂] with cis-N,N arrangement and chloride or methoxy ligand cis to the Re=O moiety. A thorough study of the calculated structures clearly shows that molecular structure of complexes [ReOX(N–O)₂] is predominantly governed by multiply bonded oxo ligand, but the isomeric preferences may be tuned by careful selection of N–O ligands.     

Synthesis, properties and thermal studies of oxorhenium(V) complexes with 3-hydrazino-5,6-diphenyl-1,2,4-triazine, benzimidazolethione and 2-hydrazinobenzimidazole. Mixed ligand complexes, pyrolytical products and biological activity

A series of biologically active complexes of oxorhenium(V), were prepared by using the organic ligands 3-hydrazino-5,6-diphenyl-1,2,4-triazine (HL1), benzimidazolethione (H2L2) and 2-hydrazinobenzimidazole (H2L3). The mixed ligand complexes of oxorhenium(V) with the previous ligands and one of the following ligands: NH4SCN, 1,10-phenanthroline (1,10-phen), 8-hydroxyquinoline (8-OHquin) or glycine (Gly), were isolated. All the binary and mixed ligand complexes have monomeric structures and exist in the octahedral configuration. Thermal studies on these complexes showed the possibility of structural transformation from mononuclear into binuclear ones. The structures of all complexes and the corresponding thermal products were elucidated by elemental analyses, IR, electronic absorption and 1H NMR spectra, magnetic moments, conductance and TG-DSC measurements. The antifungal activities of the metal complexes towards Alternaria alternata and Aspergilus niger were tested and showed comparable behaviour with some well known antibiotics.     

Synthesis and structural characterization of new oxorhenium and oxotechnetium complexes with XN2S-tetradentate semi-rigid ligands (X = O, S, N)

Twelve novel oxo-technetium and oxo-rhenium complexes based on N2S2-, N2SO- or N3S-tetradentate semi-rigid ligands have been synthesised and studied herein. By reacting the ligands with a slight excess of suitable [MO]3+ precursor (ReOCl3(PPh3)2 or [NBu4][99gTcOCl4]), the monoanionic complexes of general formula [MO(Ph-XN2S)]- could be easily produced in high yield. The complexes have been characterized by means of IR, electrospray mass spectrometry, elemental analysis, NMR and conductimetry. The crystal structures of [PPh4][ReO(Ph-ON2S)] 1b and [NBu4][99gTcO(Ph-ON2S)] 1c have been established. The [MO]3+ moiety was coordinated via the two deprotonated amide nitrogens, the oxygen and the terminal sulfur atoms in 1b and 1c. In both compounds, the ON2S coordination set is in the equatorial plane, and the complexes adopted a distorted square-pyramidal geometry with an axial oxo-group. The chemical and structural identity of the different prototypic complexes (rhenium, 99gTc complexes and their corresponding 99mTc radiocomplexes) have been also established by a comparative HPLC study.