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

Different types of polymers can be intercalated into alpha-RuCl3 with diffe rent synthetic methodologies. Polyaniline/alpha-RuCl3 nanocomposite was pre pared by the in situ redox intercalative polymerization method, in which al pha-RuCl3 was exposed to an aniline/acetonitrile solution in open air. Wate r-soluble polymers such as poly(ethylene oxide), poly(vinyl pyrrolidone), a nd polyethylenimine were intercalated by an encapsulative precipitation met hod using monolayer suspensions of alpha-RuCl3. A modification of this meth od led to insertion of polypyrrole. Monolayer suspensions of alpha-RuCl3 ca n be prepared from LixRuCl3 (x similar to 0.2). The latter is produced by t he reaction of alpha-RuCl3 with 0.2 equiv of LiBH4. The polymer insertion i s topotactic and does not cause structural changes to the host. The metal c hloride layers in these materials possess mixed valency. The reduction and polymer intercalation of alpha-RuCl3 alters the intralayer and interlayer R U3+ (low spin d(5)) magnetic coupling, so that interesting magnetic propert ies 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 t he charge transport properties are changed dramatically. For example, LixRu Cl3 shows an electrical conductivity 3 orders of magnitude higher than pris tine alpha-RuCl3 at room temperature and L-x(PEO)(y)RuCl3 has an ion conduc tivity comparable with the best (Lithium salt)-polymer electrolytes. For a comprehensive understanding of the structure of the representative nanocomp osite Li-x(PEO)(y)RuCl3, the arrangement of polymer chains inside the galle ries was explored with analysis of its one-dimensional (00l) X-ray diffract ion pattern. Calculated electron density maps along the stacking c-axis lea d 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 consi stent PEO arrangement in the gallery generates oxygen-rich channels in the middle of the gallery in which the Li ions can reside. The new nanocomposit es were characterized with thermogravimetric analysis, infrared spectroscop y, powder X-ray diffraction, magnetic measurements, as well as electrical a nd ionic conductivity and thermopower measurements.