A sandwich-type POM containing mixed cations: synthesis, thermal performance and proton-conducting properties

• Published in: Journal of coordination chemistry 2016-02, Vol.69 (3), p.425-432
• Main Authors: Li, Shujun, Zhang, Fanyu, Peng, Qingpo, Chen, Xuenian, Wang, Ruoya, Wang, Zhifang, Ma, Fengji, Zhao, Qianyi, Wei, Meilin
• Format: Article
• Language: English
• Subjects: Alternating current; Cations; Cluster compounds; Crystal structure; Networks; polyoxometalates; Polyoxometallates; proton conduction; Relative humidity; sandwich-type; thermal behavior; Thermal decomposition; Three dimensional
• ISSN: 0095-8972; 1029-0389
• DOI: 10.1080/00958972.2016.1138106

A new sandwich-type polyoxometalate, Na 5 H[N(CH 3 ) 4 ] 2 [Co(C 3 N 2 H 4 ) 2 (H 2 O) 4 ][Co 4 (H 2 O) 2 (PW 9 O 34 ) 2 ]·21H 2 O (1), has been synthesized. 1 is composed of a Weakley-type polyanion, [Co 4( H 2 O) 2 (PW 9 O 34 ) 2 ] 10− , four kinds of cations (five Na + , two [N(CH 3 ) 4 ] + , one [Co(C 3 N 2 H 4 ) 2 (H 2 O) 4 ] 2+ , and one H + ), and 21 crystalline H 2 O molecules. The surface oxygen of the polyanion in 1, the crystalline water, and coordinated water molecules make an extended 3-D hydrogen-bonding network. Alternating current (AC) impedance experiments of 1 reveal good proton conductivity for 1 of 5.03 × 10 − 4 S cm −1 at 25 °C under 98% relative humidity (RH). Activation energy of 1 calculated from Arrhenius plots is 0.358 eV, indicating Grotthuss mechanism is dominant in the proton transfer. Thermal decomposition behavior of 1 was examined by thermogravimetry/mass spectrometry (TG/MS) measurements.