Humidity-Sensing Properties of an 1D Antiferromagnetic Oxalate-Bridged Coordination Polymer of Iron(III) and Its Temperature-Induced Structural Flexibility.

A novel one-dimensional (1D) oxalate-bridged coordination polymer of iron(III), {[NH(CH)(CH)][FeCl(CO)]} (), exhibits remarkable humidity-sensing properties and very high proton conductivity at room temperature (2.70 × 10 (Ω·cm) at 298 K under 93% relative humidity), in addition to the independent antiferromagnetic spin chains of iron(III) ions bridged by oxalate groups ( = -7.58(9) cm). Moreover, the time-dependent measurements show that could maintain a stable proton conductivity for at least 12 h. Charge transport and magnetic properties were investigated by impedance spectroscopy and magnetization measurements, respectively. Compound consists of infinite anionic chains [FeCl(CO)] and interposed diethylmethylammonium cations (CH)(CH)NH, which act as hydrogen bond donors toward carbonyl oxygen atoms. Extraordinarily, the studied coordination polymer exhibits two reversible phase transitions: from the high-temperature phase to the mid-temperature phase at T ~213 K and from the mid-temperature phase to the low-temperature phase at T ~120 K, as revealed by in situ powder and single-crystal X-ray diffraction. All three polymorphs show large linear thermal expansion coefficients.