Multiple-Hydrogen-Bond Approach to Uncommon Pd(III) Oxidation State: A Pd–Br Chain with High Conductivity and Thermal Stability

A Br-bridged
Pd chain complex with the Pd ion in an uncommon +3
oxidation state, [Pd­(dabdOH)2Br]­Br2 (3), was prepared using a new method involving multiple hydrogen bonds.
The PdBr chain complex exhibited superior electrical conductivity
and thermal stability. An in-plane ligand with an additional hydrogen
donor group (hydroxy group), (2S,3S)-2,3-diaminobutane-1,4-diol (dabdOH), was used to create a multiple-hydrogen-bond
network, which effectively shrinks the Pd–Br–Pd distance,
stabilizing the Pd­(III) state up to its decomposition temperature
(443 K). 3 shows semiconducting behavior with quite high
electrical conductivity (3–38 S cm–1 at room temperature), which is 106 times larger than
the previous record for analogous PdBr chains. Indeed, 3 is the most conductive MX-type chain complex reported so far. The
precise positional control of ions via a multiple-hydrogen-bond network
is a useful method for controlling the electronic states, thermal
stability and conductivity of linear coordination polymers.