Influence of the Torsion Angle in 3,3′-Dimethyl-2,2′-bipyridine
on the Intermediate Valence of Yb in (C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>Yb(3,3′-Me<sub>2</sub>‑bipy)
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Abstract
The synthesis and X-ray crystal structures
of Cp*<sub>2</sub>Yb(3,3′-Me<sub>2</sub>bipy) and [Cp*<sub>2</sub>Yb(3,3′-Me<sub>2</sub>bipy)][Cp*<sub>2</sub>YbCl<sub>1.6</sub>I<sub>0.4</sub>]·CH<sub>2</sub>Cl<sub>2</sub> are described.
In both complexes, the NCCN torsion angles
are approximately 40°. The temperature-independent value of <i>n</i><sub>f</sub> of 0.17 shows that the valence of ytterbium
in the neutral adduct is multiconfigurational, in reasonable agreement
with a CASSCF calculation that yields a <i>n</i><sub>f</sub> value of 0.27; that is, the two configurations in the wave function
are f<sup>13</sup>(π*<sub>1</sub>)<sup>1</sup> and f<sup>14</sup>(π*<sub>1</sub>)<sup>0</sup> in a ratio of 0.27:0.73, respectively,
and the open-shell singlet lies 0.28 eV below the triplet state (<i>n</i><sub>f</sub> accounts for f-hole occupancy; that is, <i>n</i><sub>f</sub> = 1 when the configuration is f<sup>13</sup> and <i>n</i><sub>f</sub> = 0 when the configuration is
f<sup>14</sup>). A correlation is outlined between the value of <i>n</i><sub>f</sub> and the individual ytterbocene and bipyridine
fragments such that, as the reduction potentials of the ytterbocene
cation and the free x,x′-R<sub>2</sub>-bipy ligands approach
each other, the value of <i>n</i><sub>f</sub> and therefore
the f<sup>13</sup>:f<sup>14</sup> ratio reaches a maximum; conversely,
the ratio is minimized as the disparity increases
