α-RuCl₃/Polymer Nanocomposites:  The First Group of Intercalative Nanocomposites with Transition Metal Halides

Different types of polymers can be intercalated into α-RuCl 3 with different synthetic methodologies. Polyaniline/α-RuCl 3 nanocomposite was prepared by the in situ redox intercalative polymerization method, in which α-RuCl 3 was exposed to an aniline/acetonitrile 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-RuCl 3 . A modification of this method led to insertion of polypyrrole. Monolayer suspensions of α-RuCl 3 can be prepared from Li x RuCl 3 ( x ∼ 0.2). The latter is produced by the reaction of α-RuCl 3 with 0.2 equiv of LiBH 4 . 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-RuCl 3 alters the intralayer and interlayer Ru 3+ (low spin d 5 ) magnetic coupling, so that interesting magnetic properties appear in the nanocomposites. In addition, the reduction brings in free hopping electrons to the RuCl 3 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 RuCl 3 shows an electrical conductivity 3 orders of magnitude higher than pristine α-RuCl 3 at room temperature and Li x (PEO) y RuCl 3 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 RuCl 3, the arrangement of polymer chains inside the galleries was explored with analysis of its one-dimensional (00 l ) 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−HgCl 2 . 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.