ELECTRONIC-STRUCTURES AND SPECTRA OF TRINUCLEAR CARBONYL-COMPLEXES

Detailed experimental studies of the electronic spectra of trinuclear metal carbonyls have been made. An extended Hückel molecular orbital calculation on D3h, Ru3(CO)12 has been performed to aid in assigning the spectra of the triangular cluster complexes. A band at 390 nm (2.56 μm-1) in the spectrum of Ru3(CO)12 is polarized in the plane of the Ru3 triangle, exhibits an MCD A term, and blue shifts and sharpens on cooling to 77 K. This band is assigned to the 1 A1'→1E' (xz (bonding) → xz (antibonding)), or σ→σ* transition. A weak band at 320 nm (3.12 μm-1) is assigned to the 1A1' → 1E' (z2 (antibonding) → xz (antibonding)), or μ'→μ* transition. Similar evidence suggests that bands at 330 (3.03 μm-1) and 385 nm (2.60 μm-1) in the spectrum of Os3(CO)12 be assigned to σ→σ* and σ*'→*σ* transitions, respectively. The relative energies of the σ→ σ* and σ*→*σ* transitions in the M3(CO)12, Ru3(CO)9(PR3)3, and FenRu3-n (CO)12 (n=0-3) molecules depend on the ligand field splitting of the xz and z2 orbitals in the corresponding M(CO)4 and Ru(CO)3PR3 fragments. A single crystal polarized spectrum of Fe3(CO)12 shows that the two lowest energy bands at 602 and 437 nm (1.66 and 2.29 μm-1) are polarized in the plane of the Fe3 triangle. These bands are assigned to the σ*'→σ* and σ*'→σ* transitions, respectively. Intense bands (Єm >25 000) at approximately 4.0 μm-1 are assigned to MLCT transitions in the M3(CO)12 molecules. An MO scheme for the D4h molecules M2Fe(CO)14 (M=Mn, Re) is presented. The lowest energy allowed transition in each of these molecules is predicted to be of the metal-metal σ to σ* type (1A1g → 1 A2u (a2u → 2alg)). The lowest energy band in the spectrum of Re2Fe(CO)14 (2.63 μm-1) is polarized along the ReFeRe axis, consistent with the 1 Alg → 1A2u assignment. © 1978, American Chemical Society. All rights reserved.