Nitro-substituted benzoates of dimolybdenum: the Mo24+ δ to ligand charge transfer band
1996; Elsevier BV; Volume: 243; Issue: 1-2 Linguagem: Inglês
10.1016/0020-1693(96)04918-3
ISSN1873-3255
AutoresMalcolm H. Chisholm, John C. Huffman, Suri S. Iyer, Matthew A. Lynn,
Tópico(s)Polyoxometalates: Synthesis and Applications
ResumoThe preparation and characterization of a series of Mo2(O2CAr′)4 compounds, where Ar′ is a nitrosubstituted phenyl group, are described. The introduction of the NO2 group in the 4- (para) position causes a significant red-shift of a metal-to-ligand charge transfer (MLCT) band such that these compounds are intensely purple in solution: λmax ca. 540 nm with ε ∼ 15 000 M−1 cm−1. The cinnamate derivative (O2CCHCHPh-4-NO2) shows a further red-shift of this MLCT band while the 3-NO2 (meta) derivatives are only slightly red-shifted compared to the parent benzoate Mo2(O2CPh)4. The cyclic voltammograms for Mo2(O2CR)4, where R = Me, tBu, n-octyl, Ph, C6H4-4-NO2, and C6H4-3-NO2 reveal how substituents on R influence the ease of oxidation from the δ orbital. The structure of Mo2(O2CC6H4-3-NO2)4 was determined by a single crystal X-ray diffraction study as its pyridine adduct with additional pyridine in the lattice. Crystal data for Mo2(O2CC6H4-3-NO2)4(py)2·2py at −174°C: a = 10.982(2) Å, b = 20.457(4) Å, c = 10.615(2) Å, α = 93.82(1)°, β = 90.49(1)°, γ = 98.31(1)°, Z = 2, dcalc = 1.65 g cm−3 and space group P1. The nature of the MLCT band is discussed in the light of Fenske-Hall MO calculations on Mo2(O2C6H5)4, Mo2(O2C6H4-4-NO2)4, Mo2(O2CC6H4-3-NO2)4, and Mo2(O2C6H3-2-Cl-4-NO2)4.
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