CHIROPTICAL PROPERTIES OF COMPOUNDS CONTAINING METAL-METAL BONDS. SYNTHESES STRUCTURES, AND THE MEASUREMENT AND INTERPRETATION OF ELECTRONIC AND CIRCULAR DICHROISM SPECTRA OF Rh24(EtOH)2 AND Rh24(THF)2

Article abstract of DOI:10.1021/ja00266a016

The preparation, the electronic and circular dichroism spectra in solution, and the crystal and molecular structures of two chiral dirhodium tetracarboxylato complexes are reported.Rh2<(S)-mandelate>4(EtOH)2 (1) was prepared by reaction of RhCl3*3H2O and (S)-mandelic acid (α-hydroxy-α-phenylacetic acid) in aqueous solution in the presence of dimethylformamide, followed by recrystallization from ethanol.Compound 1 crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 9.027(2) Angstroem,b = 27.110(5) Angstroem, c = 32.656(5) Angstroem, V = 7991(4) Angstroem³, and Z = 8.The structure was refined to least-square residuals of R = 0.0455, R_w = 0.0551, and quality-of-fit = 1.026.Rh2<(R)-α-methoxy-α-phenylacetate>4(THF)2(2), prepared by reaction of RhCl3*3H2O with (R)-α-methoxy-α-phenylacetic acid in water/ethanol, followed by extraction with THF, crystallizes in the triclinic space group P1 with a = 11.263(2) Angstroem, b = 20.544(3) Angstroem, c = 10.325(2) Angstroem, α = 91.83(1)deg, β = 110.21(1)deg, γ = 89.11(1) deg, V= 2234.5(6) Angstroem³, and Z = 2.The structure was refined to least-squares residuals of R = 0.0460, R_w = 0.0543, and quality-of-fit = 1.004.Absolute configurations wre determined for both structures.The electronic spectra of 1 and 2 have bands near 600 and 450 nm in the visible region.The circular dichroism spectrum of each compound has three prominent bands, two bands with the same sign near 600 and 450 nm and a third band at 500 nm, opposite in sign to the first two.The circular dichroism effects are interpreted in terms of a static-coupling mechanism.The bands at 600 and 400 nm are assigned as electronically allowed components of the transition ?^*(Rh-Rh)->?^*(Rh-O) and ?(Rh-Rh, Rh-O)->?^*(Rh-O), repectively.The band at 500 nm is assigned as an overlap of magnetically allowed components of the same transition.