A Polymeric Technetium Compound of the Composition [Tc₂O₃(C₅Me₅)]_n

Abstract

The tricarboxylrhenium complex 1 ['I reacts with H,O, to give the trioxo-complex 2, which has proved to be an interesting and versatile starting compound for exploring the remarkable chemistry of rhenium in high oxidation states."] So far it has not been possible to carry out an X-ray structure analysis of 2 itself; however, the structure of one of its derivatives is already known, namely that of 3, which forms discrete molecules. This might also be assumed in the case of 2.In the reaction of the tricarbonyltechnetium complex 4 with perhydrol it has now been shown that the technetium species 4 behaves differently than its rhenium homologue 1. Elemental analysis, mass spectra, and, above all, an X-ray structure analysis yielded the empirical formula CioHi,Tc,O, for the product 5 in a polymeric structure. It is clear from Figure 1 that, in 5, two Tc atoms are bridged by three p-0x0 Iigands and the coordination of the Tc atoms is in each case completed by a C,Me, ring (= Cp*). These Cp* rings are, however, concomitantly a component of the neighboring units, so that the above mentioned empirical formula results. The planes of the Cp* rings and of the 0x0-bridge ligands are, crystallographically exactly parallel to one another, i.e. a kind of polydecker structure is formed (distances: Cp*-0, planes 297.3(3), Tc-0, plane 93.4(3), Tc-Cp* plane 204.0(4) pm). A striking feature is the unusually short distance (186.7(4) pm) between the two Tc atoms coupled by the three p-0x0 ligands (distance between the Cp*-bridged Tc atoms 407.7(4) pm); the shortest Tc-Tc distance recorded so far is 213(1) pm. Shorter metal-metal distances are found only in binuclear chromium complexes[5] with a minimum of 182.8(2) pm in [Cr,),1 .[61 Formally, the two technetium centers must be assigned on oxidation number of + 3.5. This would mean that the ground state has the relatively rare C J ' 7c4 6' configuration and thus a bond order of 3.5. ['] This bond order together with the three p-0x0 ligands makes the extremely short Tc-Tc distance understandable.The spectroscopic data are fully consistent with the results of the X-ray structure analysis. Thus, in the EI mass spectrum the molecular peak is clearly visible at m/z 381.6 (18 %), and the Tc-0 stretching vibrations appear in the IR spectrum at 909 (symmetric) and 880 cm-' (antisymmetric). In the 'H NMR spectrum the methyl protons are observed at 6 = 1.606. ExperimentalA solution of4 (1 80 mg, 0.57 mmol) in C,H, (15 mL) was treated with S mL of 30% H 2 0 2 and the mixture stirred at room temperature. The initial concentration of 4 first started to decrease after 24 h. After 3 days, 4 could no longer he detected. After separation of the phases the organic phase was dried with Na2S0, and freed of oily reaction products by chromatography (silica gel 60, 30 x 20 cm, C,H,). Subsequent elution with C,H,/diethyl ether (l/l) gave a yellow zone. After slow evaporation of solvent from the eluate (ca. 12 h), 5 was recovered in the form of needle-shaped yellow crystals. Yield: 25.0 mg (16.0 %). 99Tc 51.6...

Synthesis, reactions and structure of Cp′Tc(CO)3 derivatives

“…The C-C distances within the ring are comparable with those in other transition metal complexes containing the η 5 -C 5 Me 5 ligand with an average value of 1.4228 (6) Å. The distance between the projection of the technetium atom on the ring is 1.94(4) Å.…”

“…On a small scale, acylation of the ring ligand with benzoyl chloride to Synthesis, reactions and structure of Cp´Tc(CO) 3 3 ] has also been achieved [5]. A polymeric oxotechnetium complex, [Tc 2 O 3 (C 5 Me 5 )] n has been prepared recently from the reaction of C 5 Me 5 Tc(CO) 3 (2) with perhydrol [6]. Complex 2 is briefly mentioned there but no details of its synthesis, characterization or stereochemistry are given.…”

New Organometallic Technetium Complexes in High and Low Oxidation States

“…In the technetium case we hoped to apply the same method. Oxidation with H2O2 to Cp*Tc03 failed and we could not even isolate the polymer [Cp*Tc203]n described by Kanellakopulos and coworkers [26]. The attempt to oxidize with Mn207 failed as well and the Observation was made that some reactive intermediate or the educt technetium Compound catalytically decomposed MnzOy.…”

Technetium

“…95 The x-ray structures o f compounds (21) and (22) which is expected based on analogy to rhenium chemistry. 101 The characterization (including an x-ray structure determination) o f (26) as a polymer has caused some controversy, because o f the "supershort" Tc-Tc bond length o f 0.1867(4) nm (compare with 0.241 n m for (24) and because the spectroscopic data (IR, NMR) reported for (26) (26). This paper suggests that the Tc-Tc bond is best described as a 2 (7i5) 8*, with a bond order o f 2.5.…”