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 154

Fig. 9.4 1D chain structure
of [Pt 2 (MeCS 2 ) 4 I] 1 (1) in the
HT phase (403 K) with an
atomic numbering scheme
and relevant interatomic
distances [ 46 ]

distances along the a and c directions in 2 are 8.719 and 9.285 ˚ , respectively,
lengthened by 0.300 and 2.467 ˚ ,incomparisonwiththoseof1.
Variable temperature X-ray crystal structure analyses by Ozawa, Toriumi et al.
have revealed that 1 undergoes a structural phase transition near T trs ¼

373.4 K and
the space group changes from C 2/ c at room temperature to A 2/ m at high tempera-
ture [ 46 ] (Fig. 9.4 ). Crystallographic mirror planes perpendicular to the 1D chain
exist on the I1 atoms and the midpoint of Pt1 and Pt1 0 atoms (i.e., y ¼ 0, 0.5, 1) and,

therefore, the dinuclear units in the high-temperature (HT) phase at 403 K adopt
two staggered arrangements with twist angles of 19.4 and 19.4 , respectively [ 46 ].

Whereas, the positional disorder of PtS 4 planes is not observed for 2 in the X-ray
analysis up to 377 K, consistent with DSC data [ 32 ].

¼

9.2.2.2 [Pt 2 (RCS 2 ) 4 I] 1 (R n-Pr (3), n-Bu (4), and n-Pen (5))

RT Phases of [Pt 2 (RCS 2 ) 4 I] 1 (R ¼ n -Pr (3), n -Bu (4), and n -Pen (5))

With increasing motional degrees of freedom in the system by the elongation of
the alkyl chains in dithiocarboxylato ligands, [Pt 2 (RCS 2 ) 4 I] 1 (R ¼ n -Pr (3)[ 50 ],

n -Bu (4)[ 51 ], and n -Pen (5)[ 52 ]) undergo two phase transitions at near 210 K and
above room temperature, indicating the presence of the low temperature (LT), room
temperature (RT), and high-temperature (HT) phases. The transition temperature
and the entropy gain at the phase transition of 3-5 are listed in Table 9.1 . RT phases
of [Pt 2 (RCS 2 ) 4 I] 1 (R ¼ n -Pr (3), n -Bu (4), and n -Pen (5)) crystallize in the same

tetragonal space group I 4/ m and have almost similar structures [ 33 - 35 ]. The 1D
chain structures of 3-5 in the RT phases are shown in Fig. 9.5 . Since these crystal
structures are very similar, the RT phase of 4 is described here [ 33 ].
The structure consists of neutral 1D chains with a repeating -Pt-Pt-I- unit lying
on the crystallographic fourfold axis parallel to the c axis. The unit cell dimension c
along the 1D chain direction consists of three -Pt-Pt-I- units. Crystallographic