Geometrical isomer preference of RuII and RuIII: chemistry and structure of a RuS4P2 family. Crystal structure of [Ru(PhCH2SCS2)2(PPh3)2]
Abstract
The syntheses of mixed thioxanthate (trithiocarbonate)–phosphine complexes of types cis-[Ru(RSCS2)2(PPh3)2](1) and trans-[Ru(RSCS2)2(PPh3)2]PF6(2+) are reported (R = Et, Pri, or PhCH2). These along with trans-[Ru(RSCS2)2(PPh3)2](2) and cis-[Ru(RSCS2)2(PPh3)2]+(1+) constitute an electrochemically observable redox isomerisation cycle. The formal potentials of the couples (1+)–(1) and (2+)–(2) are ≈ 0.65 and ≈ 0.33 V respectively vs. saturated calomel electrode (s.c.e.). The isomerisation steps are (1+)→(2+)(fast) and (2)→(1)(k≈ 7.0 × 10–2 s–1). The X-ray structure of complex (1; R = PhCH2) has been determined: space group C2/c, a= 18.676(7), b= 10.511(2), c= 24.432(8)Å, and Z = 4. The superior stability of the cis configuration of RuII for complexes (1) arises primarily from the strong back-bonding (cis > trans) within the Ru(PPh3)2 fragment. For RuIII, in which back-bonding is unimportant, the stable geometry is trans owing to favourable steric disposition of the PPh3 molecules. The frozen glass e.s.r. spectra of complexes (2+) have a sizable axial distortion (Δ≈ 8 500 cm–1) with a relatively small rhombic component (V≈ 2 200 cm–1). One of the two predicted transitions (ν1≈ 7 500 and ν2≈ 9 900 cm–1) within the t2g shell is observable (ν1≈ 6 500 cm–1) in the near-i.r. region.
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