Metallo-dithiolenes ligand structure

The most detailed spectroscopic and electronic structure studies of metallo-mono(dithiolenes) have focused on the nature of ligand-to-ligand charge transfer (LLCT) excitations in [M(diimine)(dithiolene)] complexes (112, 250-257, 262, 264, 295-301) and in monooxo molybdenum dithiolenes (19, 20, 22, 23) as models for pyranopterin molybdenum enzymes such as sulfite oxidase (SO). Since metallo-mono(dithiolenes) generally possess little or no symmetry, detailed spectrosopic and electronic structure studies of this class of metallo-dithiolenes have only recently begun to appear. The analysis of the spectroscopic data has been aided by the fact that the dithiolene-to-metal charge... 

The electronic structure and spectroscopy of metallo-bis(dithiolenes) are considerably more complicated than that of the metallo-mono(dithiolenes) discussed in Section II.C because there are now two dithiolene donors, which result in twice as many sulfur-based MOs that contribute to the overall metal-ligand bonding scheme. The result is an increase in the density of states in the valence region, with a concomitant increase in the number of Sdithioiene — M CT excitations. Nevertheless, numerous spectroscopic studies and bonding calculations have been undertaken in order to explain the unique electronic properties of these molecules. The fact that two dithiolene ligands are now coordinated to... 

The ability of the dithiolene ligand to promote in-plane spin delocalization in metallo-bis(dithiolenes) has been determined using [Cu(mnt)2]2, which possesses an unpaired electron in an in-plane b g (d ) orbital (390). This electronic structure allows a detailed comparison with the out-of-plane 7t-type spin delocalization present in square-planar nickel bis(dithiolenes). Interestingly, the measured spin delocalization onto the dithiolene ligands in [Cu(mnt)2]2 is remarkably different from that determined for [Ni(mnt)2]1-and [Ni(tds)2]1. The ESEEM studies on the [Cu(mnt)2]2 ion doped in a diamagnetic [Ni(mnt)2]2 host have determined that 50% of the unpaired spin... 

Perhaps the most extensively studied metallo-bis(dithiolenes) that possess more elaborated dithiolene donors are those that utilize the dmit ligand, and DFT calculations have recently been used to investigate the nature of the ground-state one-electron levels of [Ni(dmit)2)], [Pt(dmit)2)], and [Pt(dmit)2)J (380). Despite the increased complexity of the dithiolene ligands in these complexes (Fig. 36), their electronic structure is remarkably similar to that of the simple or parent metallo-bis(dithiolenes) that have been discussed previously. This finding is most evident in the electron density contour plots of the HOMOs and LUMOs for [Ni(S2C2Me2)2], [Ni(dmit)2], and [Ni(H2 timdt)2)], and these are presented in Fig. 37. An atomic orbital population analysis reveals that the HOMO possesses b u symmetry, and is almost entirely comprised of out-of-plane ligand pn orbitals with only a few percent metal... 

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