Co-ordination chemistry of higher oxidation states. Part 32. Synthetic, spectroscopic, and electrochemical studies of some trans-[OsL2X4]–[OsL2X4]–systems (L = PR3, AsR3, SbR3, SeMe2, or pyridine; X = Cl or Br). Crystal structure of [PPh4][Os(PEt3)2Cl4]
- 1 January 1990
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 1,p. 339-347
- https://doi.org/10.1039/dt9900000339
Abstract
The preparations of trans-[OsL2X4](L = PEt3, PPh3, PEt2Ph, PEtPh2, AsEt3, AsPh3, SbPh3, SeMe2, or pyridine; X = Cl or Br) are described. Reduction of these with ascorbic acid in ethanol in the presence of PPh4 + or NEt4 + ions (and in other ways) leads to [OsL2X4]– ions. Both series of complexes were characterised by analysis, i.r., and u.v.–visible spectroscopy, and magnetic measurements. The paramagnetic [Os(PR3)2X4] show sharp 31P-{1H} n.m.r. resonances with very large low-frequency shifts (ca.–1200 p.p.m.). Assignments are proposed for the major features in the u.v.–visible spectra in terms of intraconfigurational, d–d, and ligand-to-metal charge-transfer transitions. Cyclic voltammetry has been used to study the osmium(IV)–osmium(III) couples in these systems, and the redox potentials correlated with the energies of the lowest charge-transfer transitions in the u.v.-visible spectra. The X-ray structure of [PPh4][trans-Os(PEt3)2Cl4] has been determined: space group P21/n with a= 12.225(2), b= 17.882(1), c= 18.551(2)Å, β= 103.22(1)°, Z= 4; least-squares refinement converged to R= 0.053 (R′= 0.048). The anion has approximate D4h symmetry with Os–Cl 2.375(3)–2.386(2)Å and Os–P 2.371(3), and 2.386(3)Å.Keywords
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