Dithiolenes moiety

Unfortunately, whatever the metallocenium and the metal bis-dithiolene moiety, no fractional oxidation state compound with formula (Cp 2M ) [M(M02] (with x < 1) has been reported in the literature. Concerning (Cp 2M )[Ni(dmit)2] (M = Fe, Cr, Mn), all our attempts to obtain chemically or electrochemically (Cp 2M )x[Ni(dmit)2] (with x < 1) have resulted in the synthesis of noncrystalline samples as sticky powders or mixture of fibers and grains, whose characterization was not possible. Therefore the combination between M(dmit)2 and metallocenium has been unsuccessful to obtain magnetic molecular conductors. 

EPR. The frozen solution EPR spectrum of 75 shown in Fig. 13 exhibits rhombic symmetry typical of a Ni(III) bis(dithiolene) complex (126), with g-tensor values of gx = 2.13, gy = 2.04, g, = 1.99. The nickel dimer can thus be viewed as a classical bis(dithiolene) moiety with a 3B3g ground state where the odd electron orbital composed primarily of a metal dyZ orbital and sulfur 2pz orbitals. The Ni(II) in the pz, as expected, is EPR silent (19, 122). 

Figure 1 Classification of Mo-MPT enzymes. Structures (l)-(3) represent oxidized active-site structures (only the dithiolene moiety of each MPT-based ligand is shown)...

The evolutionarily conserved Moco biosynthetic pathway consists of three steps (Scheme 1) (1) the conversion of a guanosine derivative (probably guanosine triphosphate) into sulfur-free Precursor Z via insertion of C-8 between the ribose C-2 and C-3 atoms, (2) sulfurization and transformation of Precursor Z into MPT, catalyzed by MPT-synthase, and (3) metal incorporation through chelation of the dithiolene moiety. Additional steps are involved in the attachment of a nucleotide to generate the dinucleotide forms found... 

After synthesis of the dithiolene moiety in MPT (53), the chemical backbone is built for binding and coordination of the molybdenum atom. Molybdenum enters the cell as the soluble oxyanion molybdate for which high-affinity transporters have been described in bacteria " which also exist in higher eukaryotes such as... 

In simple terms, the modelling of the oxosulfido-Mo(vi) active site (1) requires the combination of the two components shown in Figure 7.3 the first is the oxosulfido moiety itself (Figure 7.3(a), red boxes), the second is the mono(dithiolene) moiety (Figure 7.3(b), blue box). Active sites (2)-(4) can be similarly partitioned into related chalcogenide and dithiolenic components. It should be obvious that the modelling of Mo hydroxylase active sites is first and foremost an exercise in Mo/S chemistry, a rich but notoriously difficult area. ... 

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