The Electronic Structure of the Isoelectronic, Square-Planar Complexes [FeII(L)2
]2- and [CoIII(LBu)2]- (L2- and (LBu)2- = Benzene-1,2-dithiolates):  An 
Experimental and Density Functional Theoretical Study

Ray, Kallol; Begum, Ameerunisha; Weyhermüller, Thomas; Piligkos, Stergios; van Slageren, Joris; Neese, Frank; Wieghardt, Karl

doi:10.1021/ja042803i

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The Electronic Structure of the Isoelectronic, Square-Planar Complexes [Fe^II(L)₂]^2- and [Co^III(L^Bu)₂]^- (L^2- and (L^Bu)^2- = Benzene-1,2-dithiolates): An Experimental and Density Functional Theoretical Study

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Ray, Kallol
Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society;

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Begum, Ameerunisha
Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society;

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Weyhermüller, Thomas
Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society;

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Piligkos, Stergios
Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society;

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Neese, Frank
Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society;

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Wieghardt, Karl
Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society;

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Citation

Ray, K., Begum, A., Weyhermüller, T., Piligkos, S., van Slageren, J., Neese, F., et al. (2005). The Electronic Structure of the Isoelectronic, Square-Planar Complexes [Fe^II(L)₂]^2- and [Co^III(L^Bu)₂]^- (L^2- and (L^Bu)^2- = Benzene-1,2-dithiolates): An Experimental and Density Functional Theoretical Study. Journal of the American Chemical Society, 127(12), 4403-4415. doi:10.1021/ja042803i.

Cite as: https://hdl.handle.net/21.11116/0000-0008-3898-E

Abstract

The electronic structures of two formally isoelectronic transition-metal dithiolato complexes [Fe(L)₂]^2- (1) and [Co(L^Bu)₂]^1- (2) both possessing a spin triplet ground state (S_t = 1) have been investigated by various spectroscopic and density functional methods; H₂L^Bu represents the pro-ligand 3,5-di-tert-butylbenzene-1,2-dithiol and H₂L is the corresponding unsubstituted benzene-1,2-dithiol. An axial zero-field splitting (D) of +32 cm^-1 for 2 has been measured independently by SQUID magnetometry, far-infrared absorption, and variable-temperature and variable-field (VTVH) magnetic circular dichroism spectroscopies. A similar D value of +28 cm^-1 is obtained for 1 on the basis of VTVH SQUID measurements. The absorption spectra of 1 and 2 are found, however, to be very different. Complex 1 is light yellow in color with no intense transition in the visible region, whereas 2 is deep blue. DFT calculations establish that the electronic structures of the [Fe(L)₂]^2- and [Co(L)₂]^1- anions are very different and explain the observed differences in their absorption spectra. On the basis of these spectroscopic and theoretical analyses, 1 is best described as containing an intermediate spin Fe(II) ion, whereas for the corresponding cobalt complex, oxidation states describing a d⁶ (Co^III) or d⁷ (Co^II) electron configuration cannot be unambiguously assigned. The physical origin of the large zero-field splitting in both 1 and 2 is found to be due to the presence of low-energy spin-conserved d−d excitations which lead to a large D_zz through efficient spin−orbit coupling. Differential covalency effects appear to be of limited importance for this property.