Charge Carrier Doping in the Ni(dmit)2 Simple Salts by Hydrogen-Bonding Pyridinium Cations (dmit=1,3-dithiol-2thione-4,5-dithiolate)

Three kinds of the 1:1 Ni(dmit)₂ salts with 4-(4-pyridyl)pyridinium (PP), 4-2-(4-pyridyl)ethenyl]pyridinium (P=P), and 4-2-(4-pyridyl)ethyl]pyridinium (P-P) cations have been prepared and structurally characterized. All of these crystals are composed of a multi-dimensional network of the Ni(dmit)₂ anions and the hydrogen-bonding one-dimensional cation chains. Compared with tight hydrogen bonds in the P=P and P-P chains, that in the PP chain is rather loose. The P=P and P-P salts show semiconducting behavior with high resistivity and large activation energy, while the PP salt shows the op-posite temperature dependence with low resistivity at high temperature. The thermoelectric power indicates that the PP salt is an n-doped semiconductor. The proton defects may occur in the loosely bound PP chain which results in the carrier doping in the conduction band formed by the π-π interaction of the Ni(dmit)₂ anion radicals.