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• 78656-01-6 Tc((CH₂P(C₆H₅)2)2)2Br₂ 

Relevant academic research and scientific papers

Synthesis, characterization, and electrochemical properties of tertiary diphosphine complexes of technetium: Single-crystal structure of the prototype complex trans-[Tc(DPPE)2Br2]BF4

A series of nine Tc(III)/Tc(II) pairs of complexes having the formula trans-[TcD2X2]+/0, where D represents a chelating tertiary diphosphine ligand and X represents Cl, Br, or SCN, has been synthesized and characterized. This series includes the five diphosphine ligands 1,2-bis(diphenylphosphino)ethane (DPPE), cis-bis(1,2-diphenylphosphino)ethylene (DPPV), bis(1,2-diphenylphosphino)benzene (DPPB), bis(1,2-dimethylphosphino)ethane (DMPE), and bis(1,2-diethylphosphino)ethane (DEPE). There are several preparative routes to these complexes, the most practical involving reduction of higher oxidation states of technetium by excess diphosphine and concomitant ligand substitution onto the reduced technetium center. The prototype title complex, {Tc[(C6H5)2PCH2CH 2P(C6H5)2]2Br 2}BF4, formula weight 1142.46, has been characterized by single-crystal X-ray structural analysis refined to a conventional R factor of 0.046. Hexagonal red crystals of this moiety crystallize in the trigonal space group P3 with a = 20.926 (5) ?, c = 11.178 (2) ?, and Z = 3. In this complex the technetium(III) center is approximately octahedrally coordinated with four equatorial P atoms at an average distance of 2.50 (2) ? and two trans axial Br atoms at 2.440 (1) ?. Other complexes in the series have been characterized by some combination of elemental analysis, IR and vis-UV spectrophotometry, thin-layer and high-performance liquid chromatography, magnetic measurements, and cyclic voltammetry (CV). All complexes exhibit a characteristic, intense halogen-to-technetium charge-transfer (HTTCT) band in the visible region of the spectrum. The energy of this HTTCT transition is a function of the oxidation state of the technetium, the nature of the halogen (or pseudohalogen) ligands, X, and the nature of the substituents bonded to the donor phosphorus atoms. CV shows that in N,N-dimethylformamide, with use of gold, platinum, or glassy carbon electrodes, every complex in the series exhibits a reversible Tc(III)/Tc(II) redox couple. The E°′ of this Tc(III)/Tc(II) couple depends on the nature of the coordinated halogen (or pseudohalogen) ligands and on the nature of the substituents bonded to the donor phosphorus atoms. For closely related systems, the E°′ of the Tc(III)/Tc(II) couple is linearly related to the energy of the HTTCT transition. All complexes exhibit a Tc(II)/Tc(I) cathodic wave, but only for [Tc(DPPE)2(SCN)2]0/-, [Tc(DMPE)2Cl2]0/-, and [Tc(DMPE)2Br2]0/- is this couple reversible. Under the specified experimental conditions, none of the complexes exhibit any evidence for either a reversible or an irreversible Tc(IV)/Tc(III) couple.