Crystal Structures and Properties of MMX-Chain Compounds Based on Dithiocarboxylato-Bridged Dinuclear Complexes - Material Designs and New Physical Properties in MX-and MMX-Chain Compounds - page 162

Fig. 9.11 (a) Temperature dependence of the electrical conductivity of a single-crystal
[Pt 2 (MeCS 2 ) 4 I] 1 (1) parallel to the chain axis b [ 31 ]. (b) Temperature dependence of the electrical
resistivity of a single-crystal of 1 parallel to the chain axis b

type phase transition concerning conformation change of the two PtS 4 planes has
been observed at 365-375 K. The HT disordered phase is also metallic.

9.2.5.2 [Pt 2 (EtCS 2 ) 4 I] 1 (2)

The room temperature electrical conductivity of [Pt 2 (EtCS 2 ) 4 I] 1 (2)is5-30Scm 1 ,
which is of the same order as that reported for 1 [ 32 ]. The temperature dependence of
electrical resistivity of crystal 2 along the 1D chain is represented in Fig. 9.12a .On
decreasing temperature, the electrical resistivity increases and reaches a maximum
around 235 K and then decreases down to a minimum at 205 K. Below 205 K, the
electrical resistivity behaves as a semiconductor with an activated energy of
110 meV. To confirm whether the electrical conducting behavior is metallic or not,
the thermoelectric power S has been measured (Fig. 9.12b ). Above room temperature,
the S takes the temperature-independent small negative value, VK 1 . Upon

cooling, the S slightly increases and shows a slight swelling around 260-205 K and
then changes its sign and increases rapidly. If the MMX units form a metallic band, it
is an effective half-filled band mainly composed of a Pt-Pt d

15 m

*-I pz combination
since the present compound has formally an unpaired electron per an MMX unit. For
the tight-binding approximation, the thermoelectric power of the half-filled band
(

s

1) would give the temperature-independent value, zero [ 62 - 64 ]. The observed
temperature-independent behavior of S above room temperature is consistent with the

r ¼