Electrospray
ionization (ESI) in the negative ion mode was used
to create anionic, gas-phase oxo-molybdenum complexes with dithiolene
ligands. By varying ESI and ion transfer conditions, both doubly and
singly charged forms of the complex, with identical formulas, could
be observed. Collision-induced dissociation (CID) of the dianion generated
exclusively the monoanion, while fragmentation of the monoanion involved
decomposition of the dithiolene ligands. The intrinsic structure of
the monoanion and the dianion were determined by using wavelength-selective
infrared multiple-photon dissociation (IRMPD) spectroscopy and density
functional theory calculations. The IRMPD spectrum for the dianion
exhibits absorptions that can be assigned to (ligand) C=C,
C–S, C—C≡N, and Mo=O stretches. Comparison
of the IRMPD spectrum to spectra predicted for various possible conformations
allows assignment of a pseudo square pyramidal structure with C2v symmetry, equatorial coordination
of MoO2+ by the S atoms of the dithiolene ligands, and
a singlet spin state. A single absorption was observed for the oxidized
complex. When the same scaling factor employed for the dianion is
used for the oxidized version, theoretical spectra suggest that the
absorption is the Mo=O stretch for a distorted square pyramidal
structure and doublet spin state. A predicted change in conformation
upon oxidation of the dianion is consistent with a proposed bonding
scheme for the bent-metallocene dithiolene compounds [J. Am.
Chem. Soc.19769817291742], where a large
folding of the dithiolene moiety along the S···S vector
is dependent on the occupancy of the in-plane metal d-orbital.
Redox‐active ligands impart versatility in transition metal complexes, which are attractive for photosensitizers, dye sensitized solar cells, photothermal therapy, etc. Dithiolene (Dt) ligands can transition between fully reduced and fully oxidized states. Herein, we report the syntheses, characterization, crystal structures and electronic properties of four [Cu(R2Dt0)2]+/2+ (R = Me, iPr) complexes, [Cu(iPr2Dt0)2][PF6] (1a), [Cu(iPr2Dt0)2][PF6]2 (1b), and [Cu(Me2Dt0)2][PF6] (2a), [Cu(Me2Dt0)2][PF6]2 (2b), where iPr2Dt0 = N,N′‐diisopropyl‐1,2‐piperazine dithione and Me2Dt0 = N,N′‐dimethyl‐1,2‐piperazine dithione. In addition, the molecular structure of [Cu(iPr2Dt0)2][BF4]2(1c) is also reported. Complexes 1a and 2a crystallized in the triclinic, P1 space group, and 1c crystallized in the monoclinic crystal system, space group C2/c. The single‐crystal X‐ray diffraction measurements show that the Cu(I) complexes have a distorted tetrahedral geometry, whereas the Cu(II) complex exhibits a true square‐planar geometry. Cu(I) complexes exhibit a low energy charge‐transfer band (450–650 nm), which are not observed in Cu(II) complexes. Electrochemical studies of these complexes show both ligand‐ and metal‐based redox couples.
We report a series of mononuclear monooxo Mo(IV) complexes possessing either one or two fully oxidized dithiolene ligands; [MoOCl(R2Dt0)2][X], (1 and 2), and MoO(p‐SC6H4Y)2(R2Dt0), (3 and 4), (R=Me, iPr; X=PF6, SbF6, BF4; Y=H, Cl, F, CF3, Me, tBu, OMe). Either four or two quasi‐reversible ligand‐based redox couples are detected depending upon the number of fully oxidized dithiolene ligands present. The molecular structure of 3 and 4 exhibit a large (47° to 70°) fold angle along the S⋅⋅⋅S vector of the dithione ligand. The UV‐Vis spectra of 3 and 4 exhibit a low energy charge transfer band at ∼540 nm that are red‐shifted ∼200 nm compared to the spectra of 1 and 2. Density Functional Theory (DFT) calculations show that the low energy charge transfer band of 3 and 4 is heavily influenced by ligand fold angle. Reducing the fold angle decreases the charge transfer energy, and the transition becomes more ligand‐based.
The interligand communication between non-innocent dithiolene ligands of different oxidation states has been described in a Mo system. The fully reduced ene-dithiolate (Dt2−) acts as a donor moiety to the oxidized dithione (Dt0) in an LL′CT process.
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