Tc Cl Research Articles

XAFS spectroscopic study of Tc2(O2CCH3)4X2 (X = Cl, Br)

Technetium dimers Tc2(O2CCH3)4X2 (X = Cl, Br) were synthesized and studied by X-ray Absorption Fine Structure spectroscopy (XAFS). EXAFS analysis gave for Tc2(O2CCH3)4Cl2: d Tc-Tc = 2.18(1) Å, d Tc–Cl = 2.43(1) Å and for Tc2(O2CCH3)4Br2: d Tc–Tc = 2.19(1) Å, d Tc-Br = 2.63(1) Å. The Tc Tc separations are in agreement with Raman studies while the Tc–X distances are somewhat larger. Comparison with other Tc(III) quadruply bonded dimers indicates that the carboxylate compounds exhibit larger Tc–Tc separations. The effect of the terminal ligand (nature and position) on the Tc–Tc separation is discussed.

Technetium Tetrachloride as A Precursor for Small Technetium(IV) Complexes

Polymeric technetium tetrachloride reacts with monodentate donor ligands such as THF, acetonitrile, DMSO, thioxane (1-oxa-4-thiacyclohexane), PMe2Ph, PPh3, OPPh3, or OH2 via cleavage of the polymeric network and the formation of [TcCl4(L)2] complexes. The configuration of the products is dependent on the donor atoms such that trans coordination is established with "soft" donor atoms such as sulfur or phosphorus, while cis-[TcCl4(L)2] complexes are formed with the "harder" donors oxygen or nitrogen. The ambivalent thioxane binds to technetium via the sulfur atom. The trans products are air stable and resistant to hydrolysis. The cis complexes, however, undergo stepwise hydrolysis, during which complexes of the composition [Cl3(L)2TcOTc(L)2Cl3] (L = CH3CN, DMSO, or OH2) are formed. They are the first representatives of a new class of technetium(IV) complexes with a bridging oxo ligand. The Tc-O bond lengths in these bridges are between 1.803(1) and 1.823(2) A.

The synthesis and characterization of a cationic technetium nitrosyl complex: The X-ray crystal structure of [TcCl(NO)(DPPE) 2](PF 6) · CH 2Cl 2

The reaction of the ammonium pertechnetate with a stochiometric excess of hydroxylamine hydrochloride in methanol yields a nitrosyl containing intermediate which can subsequently be reacted with reducing ligands to form nitrosyl complexes in various oxidation states. The reaction with a sixfold excess of diphenyl-phosphinoethane (DPPE) yields the Tc(I) cation [TcCl(NO)(DPPE) 2] + which can be precipitated cleanly with tetraphenylborate. The infrared spectrum displays an absorption at 1728 cm −1 which corresponds to the nitrosyl group. The ESI(+) mass spectrum displays the parent ion [TcCl(NO)(DPPE) 2] + as the only signal at 960 m/ z. The X-ray crystal structure of the hexafluorophosphate salt shows a mutually trans arrangement of the nitrosyl and chloride ligands with the two bidentate phosphine ligands coordinated in the equatorial plane. The nitrosyl and chloride ligands display the usual site disorder which makes discussion of bond lengths tenuous. However, the Tc–N–O bond angle of 179.0(2)° reflects the sp hybridization of the nitrosyl nitrogen atom. The Tc–P bonds are somewhat elongated at 2.3810(6), 2.3947(6), 2.4096(5) and 2.4321(6) Å, due to the steric congestion around the metal ion. The Tc–Cl bond is unexceptional at 2.3262(7) Å. The coordination geometry of this complex is best described as a distorted octahedron.

TcCl4(H2O)2] and [Cl3(H2O)2TcOTc(H2O)2Cl3]– two molecular intermediates of the hydrolysis of technetium(iv)

Two molecular intermediates of the hydrolysis of technetium tetrachloride, cis-[TcCl4(H2O)2] and [Cl3(H2O)2TcOTc(H2O)2Cl3], were isolated and structurally characterised, suggesting that the hydrolytic degradation of technetium(IV) compounds occurs stepwise with the polymeric 'TcO2...nH2O' as a less defined final product.

The Crucial Role of the Diphosphine Heteroatom X in the Stereochemistry and Stabilization of the Substitution-Inert [M(N)(PXP)]2+ Metal Fragments (M = Tc, Re; PXP = Diphosphine Ligand)

The nature of the heteroatom X incorporated in the five-membered PXP-diphosphine bridging chain was found to play a primary unit role both in the overall stability and in the stereochemical arrangement of nitrido-containing [M(N)(PXP)](2+) metal fragments (M = Tc, Re). Thus, by mixing PXP ligands with labile [Re(N)Cl(4)](-) and Tc(N)Cl(2)(PPh(3))(2) nitrido precursors in CH(2)Cl(2)/MeOH mixtures, a series of neutral M(N)Cl(2)(PXP) complexes (M = Tc, 1-5; M = Re, 8, 9) was collected. In the resulting distorted octahedrons, PXP adopted facial or meridional coordination, and combination with halide co-ligands produced three different stereochemical arrangements, that is, fac,cis, mer,cis, and mer,trans, depending primarily on the nature of the diphosphine heteroatom X. When X = NH, mer,cis-Tc(N)Cl(2)(PNP1), 1, was the only isomer formed. Alternatively, when a tertiary amine nitrogen (X = NR; R = CH(3), CH(2)CH(2)OCH(3)) was introduced in the bridging chain, fac,cis-M(N)Cl(2)(PN(R)P) complexes (M = Tc, 2, 3; M = Re, 8f) were obtained. Isomerization into the mer,cis-Re(N)Cl(2)(PN(R)P), 8m, species was observed only in the case of rhenium when the tertiary amine group carried the less encumbering methyl substituent. fac,cis-Tc(N)Cl(2)(PSP), 4f, was isolated in the solid state when X = S, but a mixture of fac,cis-Tc(N)Cl(2)(PSP) and mer,trans-Tc(N)Cl(2)(PSP), 4m, isomers was found in equilibrium in the solution state. A similar equilibrium between fac,cis-M(N)Cl(2)(POP) (M = Tc, 5f; M = Re, 9f) and mer,trans-M(N)Cl(2)(POP) (M = Tc, 5m; M = Re, 9m) species was detected in POP-containing complexes. The molecular structure of all of these complexes was assessed by means of conventional physicochemical techniques including multinuclear NMR spectroscopy and X-ray diffraction analysis of representative mer,cis-Tc(N)Cl(2)(PN(H)P), 1, fac,cis-Tc(N)Cl(2)(PSP), 4f, and mer,cis-Re(N)Cl(2)(PN(Me)P), 8m, compounds.

Density Functional Investigation of Metal—Metal Interactions in Mixed‐Valence d2d3 (Cr, Mo, W) and d3d4 (Mn, Tc, Re) Face‐Shared [M2Cl9]2‐ Systems.

The molecular and electronic structures of mixed-valence face-shared (Cr, Mo, W) d(2)d(3) and (Mn, Tc, Re) d(3)d(4) [M(2)Cl(9)](2-) dimers have been calculated by density functional methods in order to investigate metal-metal bonding in this series. The electronic structures of these systems have been analyzed using potential energy curves for the broken-symmetry and other spin states arising from the d(2)d(3) and d(3)d(4) coupling modes. In (d(2)d(3)) [Mo(2)Cl(9)](2-) and [W(2)Cl(9)](2-), the global minimum has been found to be a spin-doublet state characterized by delocalization of the metal-based electrons in a multiple metal-metal bond (with a formal bond order of 2.5). In contrast, weak coupling between the metal centers and electron localization are favored in (d(2)d(3)) [Cr(2)Cl(9)](2-), the global minimum for this species being a ferromagnetic S = 5/2 state with a relatively long Cr-Cr separation. The (d(3)d(4)) [Re(2)Cl(9)](2-) system also exhibits a global minimum corresponding to a metal-metal bonded spin-doublet state with a formal bond order of 2.5, reflecting the electron-hole equivalence between d(2)d(3) and d(3)d(4) configurations. Double minima behavior is predicted for (d(3)d(4)) [Tc(2)Cl(9)](2-) and [Mn(2)Cl(9)](2-) due to two energetically close low-lying states (these being S = 3/2 and S = 5/2 states for the former, and S = 5/2 and S = 7/2 states for the latter). A comparison of computational results for the d(2)d(2), d(2)d(3), and d(3)d(3) [W(2)Cl(9)](z-) series and the d(3)d(3), d(3)d(4), and d(4)d(4) [Re(2)Cl(9)](z-) series indicates that the observed trends in metal-metal distances can only be rationalized if changes in both the strength of sigma bonding and metal-metal bond order are taken into consideration. These two factors act conjointly in the W series but in opposition to one another in the Re series. In the case of the [Cr(2)Cl(9)](z-) and [Mn(2)Cl(9)](z-) dimers, the metal-metal bond lengths are significantly shorter for mixed-valence (d(2)d(3) or d(3)d(4)) than d(3)d(3) systems. This result is consistent with the fact that some degree of metal-metal bonding exists in the former (due to partial delocalization of a single sigma electron) but not in the latter (where all metal-based electrons are completely localized).

Density Functional Investigation of Metal—Metal Interactions in d4d4 Face‐Shared [M2Cl9]3‐ (M: Mn, Tc, Re) Systems.

The molecular and electronic structures of the d(4)d(4) face-shared [M(2)Cl(9)](3)(-) (M = Mn, Tc, Re) dimers have been calculated by density functional methods in order to investigate metal-metal bonding in this series. The electronic structures of these systems have been analyzed using potential energy curves for the broken-symmetry and other spin states arising from the various d(4)d(4) coupling modes, and closed energy cycles have been utilized to identify and quantify the parameters which are most important in determining the preference for electron localization or delocalization and for high-spin or low-spin configurations. In [Tc(2)Cl(9)](3)(-) and [Re(2)Cl(9)](3)(-), the global minimum has been found to be a spin-triplet state arising from the coupling of metal centers with low-spin configurations, and characterized by delocalization of the metal-based electrons in a double (sigma and delta(pi)) bond with a metal-metal separation of 2.57 A. In contrast, high-spin configurations and electron localization are favored in [Mn(2)Cl(9)](3)(-), the global minimum for this species being the ferromagnetic S = 4 state with a rather long metal-metal separation of 3.43 A. These results are consistent with metal-metal overlap and ligand-field effects prevailing over spin polarization effects in the Tc and Re systems, but with the opposite trend being observed in the Mn complex. The ground states and metal-metal bonding observed for the d(4)d(4) systems in this study parallel those previously found for the analogous d(2)d(2) complexes of V, Nb, and Ta, and can be rationalized on the basis that the d(4)d(4) dimer configuration is the hole equivalent of the d(2)d(2) configuration.

Tc(NBCl2Ph)Cl2(Me2PhP)3] und [Tc(NBH3)Cl2(Me2PhP)3] - die ersten Technetium-Komplexe mit Nitridobrücken zwischen Technetium und Bor

[Tc(NBCl2Ph)Cl2(Me2PhP)3] and [Tc(NBH3)Cl2(Me2PhP)3] – the First Technetium Complexes with Nitrido Bridges between Technetium and Boron [TcNCl2(Me2PhP)3] reacts with BCl2Ph or BH3 · THF at low temperatures under formation of complexes containing a nitrido bridge between technetium and boron. The compounds are instable and decompose at room temperature under cleavage of the N–B bonds. The pale-purple [Tc(NBCl2Ph)Cl2(Me2PhP)3] crystallizes in the orthorhombic space group Fdd2. The Tc≡N bond is only slightly lengthened by the formation of the N–B bond of 1.564(4) A. However, a considerable lengthening of the Tc–Cl bond in trans position to the nitrido ligand is observed which can be attributed to an decreasing of the structural trans influence of the nitrido moiety. A similar structural feature can be found in [Tc(NBH3)Cl2(Me2PhP)3] which is the first structurally characterized transition metal complex containing a nitrido bridge to unsubstituted borane.

Oxo-rhenium(V) mixed-ligand complexes with bidentate functionalized phosphines and tridentate Schiff base ligands

A series of monooxo-rhenium(V) mixed-ligand complexes containing bidentate functionalized phosphines and tridentate Schiff base (SB) ligands have been synthesized via ligand-exchange reactions starting from labile Re(V) precursors. A convenient route of synthesis is provided by the isolation of intermediate species such as [Re(O)(L n )Cl 3] − ( 1– 3), (L n =bidentate phosphino-phenolato or phosphino-carboxylato ligands). Subsequent addition of the relevant SB affords neutral mixed-ligand complexes of general formula [Re(O)(L n )(SB m )] ( 1– 3m). By reversing the addition of the two ligands, i.e. SB first followed by functionalized phosphine, the resulting mixed-ligand species do not change formulation. Conventional spectroscopic techniques and the single-crystal X-ray structure determination of the two representative compounds ([Re(O)(L 1)(SB a)] ( 1a) and [Re(O)(L 1)(SB b)] ( 1b)) reveal a distorted octahedral geometry around the rhenium center, with the phosphino-phenolato oxygen located trans to the oxo group and the equatorial sites filled by the SB donors and the phosphine phosphorus. It is worth noting that technetium chemistry works quite differently under the same reaction conditions. In fact, no intermediate species of the type [Tc(O)(L n )Cl 3] − can be isolated with [Tc(O)Cl(L 1) 2] and reduced [Tc(L n ) 3] being the major compounds.

The synthesis and characterization of a technetium nitrosyl complex with cis-{2-pyridyl,diphenylphosphine} coligands. The X-ray crystal structure of [TcCL 2(NO) (pyPPh 2- P, N) (pyPPh 2- P)

The reaction of the Tc(II) nitrosyl complex (Bu 4N) [Tc(NO)Cl 4] with excess pyPPh 2 in refluxing MeOH gives the bis-pyridyl-diphenylphosphine complex [TcCl 2(NO)(pyPPh 2- P, N) (pyPPh 2- P)]. The IR spectrum of the crystalline product shows a medium intensity band at 1092 cm −1 and a very strong band at 1732 cm −1 which is assigned to v(Tc=N) from the nitrosyl core. The FAB(+) mass spectrum shows the protonated parent ion of 725 m/ z and the peak associated with the loss of a chloride ligand from the parent ion of 690 m/ z. The 1H NMR spectrum of the diamagnetic Tc(1) complex shows an extended series of multiples in the aryl region between 7.0 and 9.15 ppm. The X-ray crystal structure shows an unusual cis arrangement of these bulky phosphine ligands with one of these phosphine ligands coordinated in a bidentate manner. The Tc-N bond length of 1.743(5) Å is consistent with the multiple bonding expected for the linearly bonded nitrosyl ligand. The Tc-N-O bond angle of 177.2(5)° reflects the sp hybridization of the nitrosyl-nitrogen atom. The Tc-P bonds are 2.400(2) and 2.405(2) Å, which are unexceptional, as are the Tc-Cl bonds of 2.447(2) and 2.441(2) Å. The coordination geometry of this complex is best described as a very distorted octahedron. The P-Tc-N bond angle of the chelated pyridyl phosphine ligand is 66.1(1)°, which reflects the very small bite angle imposed by the four-membered chelate ring of this phosphine. This is compensated for by a large P-Tc-P angle of 107.82(5)°, imposed by the cis-phosphine coordination of these bulky tri-aryl phosphine ligands. Crystal data for C 34 5H 29 Cl 4 N 4 OP 3Tc: triclinic space group P1, a=9.8440(3), b=13.4854(5), c=14.2401(5) A ̊ , α=106.406(1), β=96.013(1), γ=92.792(1) 2 V=1797.35(11) A ̊ 3 , with D calc=1.419 g cm −3. Structure solution based on 5018 observed reflections converged at R=5.28%, for (1>2 σ(1)); GOF=1.73.

Synthesis and Characterization of Nitrido Tc(V) and Re(V) Complexes with Ferrocenedithiocarboxylate {FcCS(2) = [Fe(C(5)H(4)CS(2))(C(5)H(5))](-)}

The first mixed technetium-iron complexes [(99g)Tc(N)(FcCS(2))(2)] {FcCS(2) = [Fe(II)(C(5)H(5))(C(5)H(4)CS(2))](-)} (1) and [(99g)Tc(N)(FcCS(2))(FcCS(2)( bigstar))](+) {FcCS(2) = [Fe(II)(C(5)H(5))(C(5)H(4)CS(2))](-); FcCS(2)( bigstar) = Fe(III)(C(5)H(5))(C(5)H(4)CS(2))} (2) have been prepared and characterized. Complex 1 was obtained by reaction of the precursor complex [(99g)Tc(N)Cl(2)(PPh(3))(2)] with the piperidinium salt of the ligand FcCS(2). The resulting biferrocene complex is formed by two FcCS(2) ligands bound to the Tc atom through the four sulfur atoms of the two CS(2)(-) groups and bridged by a Tc&tbd1;N multiple bond. The mixed-valence Fe(2+)-Fe(3+), monocationic complex 2 was isolated as secondary product of the reaction of the precursor complex [(99g)Tc(N)Cl(4)](-) with the ligand FcCS(2). It has the same composition as 1 except for the fact that the Fe(II) center of one FcCS(2) ligand has been oxidized to Fe(III). The electrochemical properties of 1 and 2 are consistent with their formulations. Cyclic voltammetric studies and controlled potential electrolyses showed that complex 1 undergoes a quasi-reversible, two-electron exchange at 0.320 V (vs ferrocene/ferrocenium couple) attributed to the oxidation of the two Fe(II) ions, while complex 2 undergoes a quasi-reversible, one-electron exchange at nearly the same potential (0.344 V) assigned to the oxidation of the residual Fe(II) ion. These results indicate that in complex 1 the two Fe(II) atoms behave as independent redox centers. The synthesis, characterization, and electrochemical behavior of the analogous, six-coordinated rhenium(V) complex [Re(N)(FcCS(2))(2)(PPh(3))] are also reported.

Ligand substitution reactions of [Tc(NO)Cl 2(PPh 3) 2(NCCH 3)] with π-acceptor ligands

The reaction of [Tc(NO)Cl 2(PPh 3) 2(NCCH 3)] with carbon monoxide in chloroform yields [Tc(NO)Cl 2(PPh 3) 2(CO)], in which the weakly coordinated acetonitrile ligand has been replaced by the carbon monoxide. The 1H NMR spectrum of this complex displays equivalent triphenylphosphine ligands, indicating mutually trans coordination geometry. The FAB(+) mass spectrum of this complex contains the hydrated parent ion of 770 m/z plus various fragments associated with the loss of the chloride and carbon monoxide ligands. The reaction of [Tc(NO)Cl 2(PPh 3) 2(NCCH 3)] with excess tert-butylisonitrile in CH 2Cl 2 at room temperature yields [Tc(NO)Cl 2(PPh 3) 2(CNtBu)], in which a single isonitrile ligand has replaced the coordinated acetonitrile. The IR spectrum of this complex displays the absorption from ν(NO) at 1737 cm −1. The FAB(+) mass spectrum of the species displays the parent ion of 806 m/z which corresponds to [Tc(NO)Cl 2(PPh 3) 2(CNtBu)] +. The reaction of [Tc(NO)Cl 2(PPh 3) 2(NCCH 3)] with excess tert-butylisonitrile in refluxing CH 2Cl 2 yields [Tc(NO)Cl 2(PPh 3)(CNtBu) 2], in which two isonitrile ligands have replaced one of the triphenylphosphines and the coordinated acetonitrile. The IR spectrum of this complex displays the absorption from ν(NO) at 1736 cm −1. The FAB(+) mass spectrum of the species displays the parent ion of 627 m/z which corresponds to [Tc(NO)Cl 2(PPh 3)(CNtBu) 2] +. The reaction of [Tc(NO)Cl 2(PPh 3) 2(NCCH 3)] with excess tert-butylisonitrile in refluxing benzene yields [Tc(NO)Cl 2(CNtBu) 3], in which three isonitrile ligands have replaced both of the phosphine ligands and the coordinated acetonitrile. The IR spectrum of this complex displays the absorptions from ν(NO) at 1751 and 1725 cm −1. The FAB(+) mass spectrum of the species displays the parent ion of 447 m/z which corresponds to [Tc(NO)Cl 2(CNtBu) 3] +.

The synthesis, characterization and substitution reactions of the mixed ligand technetium(I) nitrosyl complex trans—trans-[(NO)(NCCH3)Cl2(PPh3)2Tc

The techneium—nitrosyl complex n-Bu4N[Tc(NO)Cl4] reacts with excess triphenylphospine in refluxing acenotonitrile to give the Tc(I) mixed ligand complex [Tc(NO)Cl2(PPh3)2NCCH3 in good yield. The IR spectrum of this complex displays an absorption at 1690 cm−1 which is associated with v(NO). The FAB(+) mass spectrum shows the fragment of 723 mz which corresponds to [Tc(NO)Cl2(PPh3)2]+ which is generated from the loss of the acetonitrile ligand. The 1HNMRR spectrum of this species displays equivalent trans-triphenylphosphine ligands; however because of the liability of the acetnitrile ligand, two signals are observed from the coordinated and dissociated acetonitrile protons. The analogous reaction in the methanol gives the methanol adduct [Tc(NO)Cl2(PPh3)2HOCH3]. When pyridine is employed as solvent, the tris-pyridine complex [Tc(NO)Cl2(py)3] is isolated as the major product, with no phosphine coordination. The IR spectrum of this complex shows an absorption at 1688 cm−1 which is associated with v(NO). The FAB(+) mass spectrum shows the fragment of 436 m/z which corresponds to the parent ion [Tc(NO)Cl2(py)3]+. This diamagnetic Tc(I) complex displays a well resolved, narrow-lined 1H NMR spectrum. Crystal data for [Tc(NO)Cl2(py)3]∗d2CH3CN: monoclinic space group C2/c, (No. 15), a = 19.182(1), b = 10.8725(8), c = 11.9371(8) A, β = 116.580(7)°,V = 2226.5(6) A3, with Dcalc = 1.543 g cm−3 to give Z = 4. structure solution based on 2689 reflections converged at R = 0.025, Rw = 0.030, GOF = 1.41. The reaction chemistry of the acetonitrile adduct [Tc(NO)Cl2(PPh3)2NCCH3] with pyridine, 3,5-lutidine, bipyridine, phenanthroline and terpyridine is also presented.

The synthesis of nitrosyl complexes of technetium with sulfur-containing cores

Abstract The reaction of [Tc(NO)Cl 2 (PPh 3 ) 2 (NCCH 3 )] with 1 equiv. of potassium alkylxanthate in CH 2 Cl 2 yields complexes of the type [Tc(NO)Cl(PPh 3 ) 2 (S 2 COiBu)], in which the weakly coordinated acetonitrile ligand and one of the chloride ligands have been replaced by the bidentate, monoanionic xanthate ligand. The 1 H NMR spectrum of this complex displays equivalent triphenylphosphine ligands, indicating mutually trans coordination geometry. The IR spectrum of this complex displays the absorption associated with ν(NO) at 1702 cm −1 from the linearly coordinated nitrosyl ligand. The FAB (+) mass spectrum of this complex contains the parent ion of 837 m / z which corresponds to [Tc(NO)Cl(PPh 3 ) 2 (S 2 COiBu)] + plus various fragments associated with the loss of the chloride and phosphine ligands. The reaction of [Tc(NO)Cl 2 (PPh 3 ) 2 (NCCH 3 )] with excess potassium alkylxanthate in CH 2 Cl 2 yields complexes of the type [Tc(NO) (PPh 3 ) (S 2 COiBu) 2 ], in which two, bidentate alkylxanthate ligands have been incorporated into the reaction product. The IR spectrum of this complex displays the absorption from ν(NO) at 1701 cm −1 which indicates a linearly coordinated nitrosyl ligand. The FAB(+) mass spectrum of the species displays the parent ion of 689 m / z which corresponds to [Tc(NO) (PPh 3 ) (S 2 COiBu) 2 ] + . The 1 H NMR spectrum of this species displays inequivalent alkylxanthate ligands which indicates that the phosphine and nitrosyl ligands are coordinated in a cis conformation. The analogous reaction chemistry of [Tc(NO)Cl 2 (PPh 3 ) 2 (NCCH 3 )] with the potentially bidentate ligand 2-mercaptopyridine is also presented.

Metal-Metal Multiply Bonded Complexes of Technetium. 5.(1) Tris and Tetrakis(formamidinato) Complexes of Ditechnetium.

Compounds of the type Tc(2)Cl(4)(PR(3))(4) (PR(3) = PEt(3), PMe(2)Ph, PMePh(2)) react with the molten formamidines HDPhF (HDPhF = diphenylformamidine) and HDTolF (HDTolF = di-p-tolylformamidine) to produce mixtures of tris- and tetrakis-bridged formamidinate complexes of ditechnetium. The displacement of chloride and phosphine by [DPhF](-) was accompanied by the oxidation of the dimetal core to produce the mixed-valent complexes Tc(2)(DPhF)(3)Cl(2) (1) and Tc(2)(DPhF)(4)Cl (2) in modest yield. The solid-state structures of the di-p-tolyl analog of 1, Tc(2)(DTolF)(3)Cl(2) (1a), and Tc(2)(DPhF)(4)Cl.C(7)H(8) (2.C(7)H(8)) have been determined by single crystal X-ray diffraction studies and are described in detail. The structure of 1a consists of three formamidinate ligands spanning the two technetium atoms. The two chloride ligands, which complete the coordination sphere, are bound equatorially at distances of 2.357(1) and 2.346(2) Å from the metals. Though possessing no crystallographic symmetry, 1a approximates C(2)(v)() symmetry. The metal-metal bond length of 2.0937(6) Å ranks among the shortest reported for technetium and is indicative of a Tc-Tc multiple bond. Compound 2 crystallizes with the Tc atoms colinear with a crystallographic 4-fold axis. The four bridging formamidinate ligands are arranged in a lantern geometry about the dimetal unit. The chloride is bonded in an axial position at a distance of 2.450(4) Å. The Tc-Tc bond length of 2.119(2) Å is also consistent with the presence of a high order Tc-Tc bond. The electronic structures of 1 and 2 were investigated by means of SCF-Xalpha-SW molecular orbital calculations using the model compounds Tc(2)(HNCHNH)(3)Cl(2) and Tc(2)(HNCHNH)(4)Cl. The results support the presence of a sigma(2)pi(4)delta(2)delta ground state configuration giving rise to a formal bond order of 3.5. The LUMO in both cases is a low-lying pi orbital. The formamidinate complexes 1 and 2 have been further characterized by IR spectroscopy and cyclic voltammetry. The crystallographic parameters for 1a and 2.C(7)H(8) are as follows: Tc(2)(DTolF)(3)Cl(2) (1a), monoclinic space group P2(1)/n (No. 14) with a = 16.185(2) Å, b = 15.637(2) Å, c = 17.812(1) Å, beta = 110.142(5) degrees, V = 4232.3(6) Å(3) and Z = 4; Tc(2)(DPhF)(4)Cl.C(7)H(8) (2.C(7)H(8)), tetragonal space group P4/ncc (No. 130) with a = 15.245(2) Å, c = 21.832(3) Å, V = 5074.1(9) Å(3) and Z = 4.

Syntheses and characterization of amino and amido–imido technetium(V) and rhenium(V) complexes with (o-aminophenyl)diphenylphosphine-N,P. Crystal structures of [TcNCl{PPh2(C6H4NH2-2)}2]Cl·MeCN and [Re{PPh2(C6H4N-2)}Cl2{PPh2(C6H4NH-2}

Reactions of [NBu4][MOCl4](M = Tc or Re) or [ReOX2(OEt)(PPh3)2](X = Cl, Br or I) with the bidentate ligand (o-aminophenyl)diphenylphosphine (H2L) under controlled reaction conditions gave neutral imido-metal(V) complexes of the type [M(L)Cl2(HL)]; in particular, the neutral [Re(L)Cl2(HL)] complex 3, the crystal structure of which has been determined contains HL– and L2– ligands ‘twisted’ relative to each other by 101.3°, with the imido group bonded trans to a Cl atom, while the other chloro is equatorial. Important molecular parameters are: Re–N(2) 1.780(7), Re–N(1) 1.973(7), Re–Cl(1) 2.404(2), Re–Cl(2) 2.384(2), Re–P(1) 2.438(2) and Re–P(2) 2.492(2)A. The bent configuration of the imido core [Re–N(2)–C(12) 137.1(5)°] enforced by the intrinsic ligand geometry, along with the v(ReN–) stretch at 971 cm–1, indicates the peculiarity of this nitrene core. The severe distortion from octahedral geometry is also represented by the Cl(2)–Re–N(2) angle of 157.0(2)° and by the ‘bite’ angles of 79.5(2) and 75.2(2)° for the HL– and L2– ligand, respectively. Substitution reactions on [NBu4][TcNCl4] and [MNCl2(PPh3)2](M = Re or Tc) with H2L give cationic nitrido–metal(V) complexes of the type [MNCl(H2L)2]Cl, in which the co-ordination of two bidentate H2L chelates occurs with a mutual cis-P configuration and with the amino-N on the equatorial plane of a distorted octahedron; the site trans to the MN unit is occupied by a Cl ligand. The crystal structure of [TcNCl(H2L)2]Cl·MeCN 2 has also been determined. Relevant molecular parameters are: Tc–N(3) 1.627(3), Tc–N(1) 2.178(3), Tc–N(2) 2.205(4), Tc–Cl(1) 2.593(2), Tc–P(1) 2.427(2), Tc–P(2) 2.439(1)A, N(3)–Tc–Cl(1) 179.5(1)°.

Molecular and crystal structure of a mixed-phosphine ligand Tc(II) complex, Tc(PMe2Ph)2(DMPE)Cl2

The reaction of Tc(PMe2Ph)3Cl3 with an excess of bis(dimethylphosphino)ethane (DMPE) in ethanol solution produced a yellow compound, which was identified by X-ray diffraction methods as a mixed-ligand Tc(II) complex, Tc(PMe2Ph)2(DMPE)Cl2. The compound crystallizes in the P21/c space group with a = 12.899(6), b = 13.142(8), c = 19.088(9) Å, β = 121.13(3)°, V = 2770(2) Å3, Z = 4, R = 0.061, and Rw = 0.051. The geometry around the Tc atom is octahedral with the chloro ligands trans to each other, while the two PMe2Ph ligands are in cis positions. The Tc—Cl bond distances are 2.431 (5) and 2.431 (5) Å while the Tc—P bond lengths are 2.434(4) and 2.435(4) Å for PMe2Ph and 2.400(4) and 2.398(4) Å for the bidentate DMPE ligand. An increase of multiple bonding of the Tc—P bond, as the oxidation state of Tc decreases, is suggested.

Technetium-Carbon Multiple Bonds: Synthesis and Structure of Tc(:C:CHPh)Cl(dppe)2 and [Tc(.tplbond.CCH2-t-Bu)Cl(dppe)2

The 16-electron complex TcCl(dppe)[sub 2] reacts with terminal alkynes to form neutral vinylidene complexes of the type Tc(=C=CHR)Cl(dppe)[sub 2] (R = Ph, Me, t-Bu). Treatment of these vinylidene complexes with acid (HBF[sub 4] for R = Ph, HNMe[sub 3]BPh[sub 4] for R = t-Bu) yields the respective terminal carbyne complexes Tc([triple bond]CCH[sub 2]R)-Cl(dppe)[sub 2][sup +] (R = Ph, t-Bu). These vinylidene and carbyne compounds represent the first examples of technetium carbenes or carbynes. X-ray structures of Tc(=C=CHPh)Cl(ddpe)[sub 2] and Tc([triple bond]CCH[sub 2]-t-Bu)Cl(dppe)[sub 2[minus]+] were determined, and the Tc-C bond lengths obtained were 1.861(9) and 1.724(7) A, respectively. 13 refs., 2 figs.

Technetium complexes with thioether ligands—III. Synthesis and structural characterization of cationic nitridotechnetium(V) complexes with thiacrown ethers

The first representative of a new class of TcN complexes with thiacrown ethers have been prepared by ligand exchange reaction of NBu 4[TcNCl 4] with 1,4,8,11-tetrathiacyclotetradecane (14S4), 1,5,9,13-tetrathiacyclohexadecane (16S4), 1,5,9,13-tetrathiacyclohexadecane-3,11-diole (16S4-(OH) 2) and 1,4,7,10,13,16-hexathiacyclooctadecane (18S6). The crystal structure of [TcNCl(14S4)]TcNCl 4 1) consists of couples of independent cations with the metal in the oxidation state + 5 and hexavalent TcNCl 4 − anions. In the complex cation the metal is six-coordinated in a rather distorted octahedral geometry, being directly bound to four sulphur atoms from the macrocyclic ligand in the equatorial plane and to the nitrido atom and to one chlorine atom in the axial positions. The strong trans influence of the nitrido ligand causes an extreme lengthening of the TcCl bond distance to 2.718 Å. The octahedral molecular structure of [TcNCl(18S6)]TcNCl 4 ( 3) is comparable with that of 1, but only four sulphur atoms of the thiacrown ether form the equatorial plane, two sulphur atoms remain non-coordinated, and the nitrido and Cl − ligands are in axial positions. The most interesting feature in the structure of [TcNCl(16S4-(OH) 2)]Cl ( 5) is the observation of an exceptionally long TcN distance of 1.95 Å.

Extreme covalence in the Tc–Cl bond from polarized neutron diffraction

A polarized neutron diffraction experiment on a salt containing the 4d1 TcNCl4− ion (S=1/2) yielded the flipping ratios of six reflections confined to the hk0 plane. Using nuclear structure factors, FN, extrapolated from the 123 and 295 K x-ray structures, magnetic structure factors, FM, were obtained from the flipping ratios. The values of FM were fitted to a model of spin populations in the Tc-4d and the Cl-3(sp) orbitals. It was found that 46(5)% of the spin density is located on the Cl atoms, corresponding to exceptionally high covalence in the Tc–Cl bonding. The amount is distinctly higher than found indirectly by ESR measurements, but is to some extent supported by a local density functional DV–Xα calculation. Because the data is limited to the one projection, it is not possible to separate the Tc and N spin density contributions.