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Magnetic Circular Dichroism Spectra of Compounds Containing Quadruple Metal–Metal Bonds. Polarized Single Crystal Absorption Spectra of ( n ‐Bu 4 N) 2 [Re 2 Br 8 ] at 5 K

1976; Wiley; Volume: 15; Issue: 3-4 Linguagem: Inglês

10.1002/ijch.197600052

1869-5868

Charles D. Cowman, William C. Trogler, Harry B. Gray,

Organometallic Complex Synthesis and Catalysis

Abstract It is found that only weak MCD B terms are associated with the 1 A 1s → 1 A 2u ( δ → δ *) absorption in Re 2 X 2‐ 8 (X = Cl, Br), Mo 2 Cl 4‐ 8 , and Mo 2 Cl 4 [P(C 2 H 5 ) 3 ] 4 . At 15K (KBr disk sample), the 585 nm absorption system of Mo 2 Cl 4 [P(C 2 H 5 ) 3 ] 4 shows 320 cm −1 vibronic fine structure in a 1g (MoMo). By analogy, this sytem is assigned to the spin‐allowed δ → δ * transition. The lowest energy strong MCD signals exhibited by Re 2 Cl 2‐ 8 , Re 2 Br 2‐ 8 , and Mo 2 Cl 4‐ 8 are A terms at 310, 420, and 270 nm, respectively. These are associated with the 1 A 1g → 1 E u (X(π) → δ*) transitions. Relatively intense MCD signals at 275 and 380 nm for Re 2 Cl 2‐ 8 and Re 2 Br 2‐ 8 and corresponding features in the single crystal polarized absorption spectra are assigned in each case to two overlapping transitions, 1 A 1g → 1 A 2u (X(π) → δ*) and 1 A 1g → 1 E u (X(σ) → δ*). The 440 nm absorption systems of Mo 2 (O 2 CH) 4 and Mo 2 (O 2 CCF 3 ) 4 exhibit strong MCD B terms.