Scientific article

Structure and reactivity of [Mo3-µ3S-(µS2)3]4+ complexes : quantum chemical calculations, X-ray structural characterization and Raman spectroscopic measurements

Published inInorganic chemistry, vol. 37, no. 11, p. 2633-2644
Publication date1998

A series of compounds containing the [Mo3-μ3S-(μS2)3-(dtc)3]+ complex (dtc = diethyldithiocarbamate) with the anions I- (1), I- and Br- (2), S2- (3), ClO4- (4), NO3- (5), and SO42- (6) was prepared and characterized by elemental analysis, NMR, IR, and Raman spectroscopy, and FAB mass spectrometry. The previously reported crystal structure of 1 was reinvestigated. The X-ray analysis revealed the incorporation of CH2Cl2 in the crystal having the composition [Mo3S7(dtc)3]I·0.5CH2Cl2 (1a), which was in contradiction to the previous protocol. The corresponding ClO4- compound (4a) is isotypic. Crystal data: C15.5H31Cl2Mo3N3O4S13, orthorhombic space group Aba2, a = 25.816(5) Å, b = 17.761(4) Å, c = 16.250(3) Å, Z = 8. For 1a, 4a, 6, and the previously analyzed 2 and 3 the crystal structures revealed characteristic interactions between the anions X and the three axial (out-of-plane) sulfur atoms Sax of the disulfido bridges. The Raman data showed a significant decrease of the Seq−Sax stretch resonance frequency in the order 4, 5, 6 > 1 > 3. This decrease is paralleled with a slight increase of the Seq−Sax bond length and with a significant shortening of the X···Sax distances when compared to the sum of the corresponding van der Waals radii. A comprehensive quantum chemical study, using both density functional theory and semiempirical calculations, revealed that for hard counterions such as NO3- and ClO4- the Sax···X interactions can be understood in terms of an almost entirely electrostatic interaction, whereas for soft nucleophiles such as I- and S2- significant covalency is observed. In addition, the general reaction of [Mo3S7]4+ complexes with a nucleophile was modeled. With regard to the side-on bonding of the μ-S2 groups to Mo, the calculations indicated a significantly higher bond energy for the axial (out-of-plane) sulfur atoms, explaining the much higher lability of the sulfur atoms in the equatorial (in-plane) position. Analogous differences for the ligating atoms of the peripheral ligands, having a cis and trans position with respect to μ3-S, are less pronounced.

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Citation (ISO format)
MAYOR-LOPEZ, Maria J. et al. Structure and reactivity of [Mo3-µ3S-(µS2)3]4+ complexes : quantum chemical calculations, X-ray structural characterization and Raman spectroscopic measurements. In: Inorganic chemistry, 1998, vol. 37, n° 11, p. 2633–2644. doi: 10.1021/ic971214t
ISSN of the journal1939-5175

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