α-RuCl₃/polymer nanocomposites: The first group of intercalative nanocoraposites with transition metal halides

Different types of polymers can be intercalated into α-RuCl₃ with different synthetic methodologies. Polyaniline/α-RuCl₃ nanocomposite was prepared by the in situ redox intercalative polymerization method, in which α-RuCl₃ was exposed to an aniline/acetonilrile solution in open air. Water- soluble polymers such as poly(ethylene oxide), poly(vinyl pyrrolidone), and polyethylenimine were intercalated by an encapsulative precipitation method using monolayer suspensions of α-RuCl₃. A modification of this method led to insertion of polypyrrole. Monolayer suspensions of α-RuCl₃ can be prepared from Li(x)RuCl₃ (x ~ 0.2). The latter is produced by the reaction of α-RuCl₃ with 0.2 equiv of LiBH₄. The polymer insertion is topotactic and does not cause structural changes to the host. The metal chloride layers in these materials possess mixed valency. The reduction and polymer intercalation of α-RuCl₃ alters the intralayer and interlayer Ru³⁺ (low spin d⁵) magnetic coupling, so that interesting magnetic properties appear in the nanocomposites. In addition, the reduction brings in free hopping electrons to the RuCl₃ layers and the polymer intercalation builds up new electronic or ionic conducting channels in the galleries, so that the charge transport properties are changed dramatically. For example, Li(x)RuCl₃ shows an electrical conductivity 3 orders of magnitude higher than pristine α- RuCl₃ at room temperature and Li(x)(PEO)(y)RuCl₃ has an ion conductivity comparable with the best (lithium salt)-polymer electrolytes. For a comprehensive understanding of the structure of the representative nanocomposite Li(x)(PEO)(y)RuCl₃, the arrangement of polymer chains inside the galleries was explored with analysis of its one-dimensional (001) X-ray diffraction pattern. Calculated electron density maps along the stacking c- axis lead to a structural model that fills each gallery with two layers of polymer chains exhibiting a conformation found in type-II PEO-HgCl₂. The most consistent PEO arrangement in the gallery generates oxygen-rich channels in the middle of the gallery in which the Li ions can reside. The new nanocomposites were characterized with thermogravimetric analysis, infrared spectroscopy, powder X-ray diffraction, magnetic measurements, as well as electrical and ionic conductivity and thermopower measurements.