Pd(III) Mott–Hubbard Compounds - Material Designs and New Physical Properties in MX-and MMX-Chain Compounds - page 51

Fig. 4.19 Potential energy
curve of the bridging bromide
ion in the (a) CDW and (b)
MH states

of 5.26 ˚ respectively. This result suggests that a dð Pd Pd Þ is the boundary

between CDW and MH states.
If the Pd-Br bond is ionic, the potential energy of the bromide ion is given by the
Born-Mayer equation. In the Pd(IV) Pd(II) mixed valence system, this

energy forms double minimum potential, which is the sum of the potential curves
for Pd(IV)

Br

Br Pd(II) (red curve) and Pd(II) Br Pd(IV) (blue curve), as

shown in Fig. 4.19 . When dð becomes shorter, the equivalent position of

the bromide ions becomes closer to each other, and finally, the double minimum
potential becomes a single minimum potential at the midpoint between two neigh-
boring Pd ions, as shown in Fig. 4.19b . In this situation, all of the Pd ions should be
equivalent, and the Pd(III) MH state should be stabilized. In the present system, we
concluded that the boundary distance between double minimum and single mini-
mum potentials was ca. 5.26 ˚ .

Pd Pd Þ

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