title: Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens.
abstract: In this work we report on water-free proton conductivity in liquid-crystal pyridylpyrazolate-based Pt(II) and Pd(II) complexes [M(pz(R(n,n)py))2] (pz(R(n,n)py) = 3-(3,5-dialkyloxyphenyl)-5-(pyridin-2-yl)pyrazolate, R(n,n) = C6H3(OCnH2n+1)2; n = 4, 12, 16, M = Pd; n = 12, M = Pt) with potential application as electrolyte materials in proton exchange membrane fuel cells. The columnar ordering of the complexes in the liquid-crystalline phase opens nanochannels, which are used for fast proton exchange as detected by impedance spectroscopy and NMR. The NMR spectra indicate that the proton conduction mechanism is associated with a novel C-H···N proton transfer, which persists above the clearing point of the material. The highest conductivity of ∼0.5 μS cm(-1) at 180 °C with an activation energy of 1.2 eV is found for the Pt(II) compound in the mesophase. The Pd(II) complexes with different chain length (n = 4, 12, and 16) show lower conductivity but smaller activation energies, in the range of 0.74-0.93 eV.
authors.forename: Cristián
authors.initials: C
authors.lastname: Cuerva
authors.forename: José A
authors.initials: JA
authors.lastname: Campo
authors.forename: Mercedes
authors.initials: M
authors.lastname: Cano
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , E-28049 Cantoblanco Madrid, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Sanz
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , E-28049 Cantoblanco Madrid, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Sobrados
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , E-28049 Cantoblanco Madrid, Spain.
authors.forename: Virginia
authors.initials: V
authors.lastname: Diez-Gómez
authors.forename: Alberto
authors.initials: A
authors.lastname: Rivera-Calzada
authors.forename: Rainer
authors.initials: R
authors.lastname: Schmidt