Proton Conduction in Paddlewheel-type Dinuclear Platinum(III) Complex System Including Neutral and Protonated 1,2,4-Triazole

1,2,4-Triazole (trz) is a heterocyclic base with high proton affinity, making it an excellent candidate as a hopping site for fast proton transport. In this study, we synthesized two paddlewheel-type dinuclear platinum complexes: (Htrz)2[Pt2(sq)4(trz)2]·3(H2O) (1) and (Bu4N)2[Pt2(sq)4(trz)2]·3(H2O) (2), where H2sq is squaric acid. Crystallographic study revealed that, in contrast to complex 2, complex 1 is the first example of an integration involving an N–H···N hydrogen-bonding interaction between neutral and protonated trz in the solid. Complex 1 exhibited a high proton conductivity of 1.0 × 10–4 S cm–1 at 25 °C and 98% relative humidity, which was significantly higher than that of 2 (8.5 × 10–8 S cm–1 under the same conditions). Infinite hydrogen-bonding networks, including trz–Htrz+ pairs, were apparently responsible for the high proton conduction observed in complex 1.