Ni(II)-Based Metallosupramolecular Polymer with Carboxylic
Acid Groups: A Stable Platform for Smooth Imidazole Loading and the
Anhydrous Proton Channel Formation
posted on 2020-06-13, 00:13authored byYemineni S L V Narayana, Takefumi Yoshida, Manas Kumar Bera, Sanjoy Mondal, Masayoshi Higuchi
The
Ni(II)-based metallosupramolecular polymer with carboxylic
acid groups (polyNi) was synthesized via a 1:1 complexation
of Ni(II) salt with (4,4′-(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(pyridine-2,6-dicarboxylic
acid) for the first time. The divalent state of Ni(II) in the polymer
was confirmed by the X-ray absorption fine structure analysis. Smooth
loading of imidazole molecules into polyNi proceeded
with the help of the carboxylic acid groups to form the imidazole-loaded polyNi (polyNi-Im). Thermogravimetric analysis
of polyNi-Im revealed that approximately three imidazole
molecules were incorporated per repeating unit of polyNi. The Fourier transform infrared spectrum of polyNi-Im showed a new peak at 3219 cm–1, which shows an
∼73 cm–1 enhancement to −N–H
of pristine imidazole. The peak suggests the formation of an imidazolium
cation in the polymer. Powder X-ray diffraction indicated no degradation
of the polymer structure during the imidazole loading because the
diffraction pattern of polyNi-Im was almost the same
as that of polyNi except for the presence of peaks corresponding
to the imidazole molecules. Interestingly, the scanning electron microscopy
measurement showed a large morphological change to uniform spherical
particles by loading imidazole to the polymer. PolyNi-Im exhibited good proton conductivity (1.05 × 10–2 mS/cm) at a high temperature (120 °C), which is around 7 orders
of magnitude higher than that of pristine polyNi because
of the proton conduction pathway formation along the polymer chains
by the incorporated imidazole molecules.