One-dimensional (1D) coordination polymers containing mixed-valent metals are expected to have outstanding electronic properties. 1D halogen-bridged mixed-valent transition-metal complexes – so-called MX- and MMX-chain families – have isolated one-dimensional d-electronic systems. In particular, some members of the MMX-chain family have high conductivity. Conductivity ranges from semiconductivity to metallic conductivity and originates from a binuclear metal unit that provides internal electronic flexibility. A representative compound, Pt₂(dta)₄I (dta: CH₃CS₂^–), is known to have high electrical conductivity.

Kazuya Otsubo and Hiroshi Kitagawa, Kyoto University, Japan, and colleagues have investigated the pressure dependence of the conductivity and lattice parameters of Pt₂(dta)₄I. They studied the compound’s conductivity and its phase diagram using a combination of Raman spectroscopy, X-ray oscillation photography, and X-ray crystallography.

The researchers demonstrated that this compound shows semiconducting behavior under pressure with no significant electronic phase transition. Comparison with an isostructural compound, Pt₂(dtp)₄I (dtp: C₂H₅CS₂^–), showed that the length of the alkyl chain on the terminal ligand is important in determining the electronic states and hence the conductivity.

• Conducting Behavior and Valence Ordering of a One-Dimensional MMX-Type Coordination Polymer under High Pressure,
  Kazuya Otsubo, Tomohiko Suto, Atsushi Kobayashi, Ryuichi Ikeda, Masato Hedo, Yoshiya Uwatoko, Hiroshi Kitagawa,
  Eur. J. Inorg. Chem. 2016.
  DOI: 10.1002/ejic.201600499