A Mössbauer study of polymers prepared from polyvinylpyridine and ferric chloride or ferric nitrate

Iron‐ion‐containing polymers were prepared by reacting atactic polyvinylpyridine with ferric chloride or ferric nitrate in methanol solution. Molar ratios of Fe3+ to 4‐vinylpyridine (Fe:PVP) were 1:2, 1:6, and 1:20. Three kinds of iron center were characterized from 57Fe Mössbauer spectra recorded over a temperature range of 4.2–290 K. Infrared (IR) spectra of the samples were measured also. All samples contained amorphous hydrated ferric‐oxide particles that exhibited superparamagnetic behavior at low temperatures. The size of the clusters (102–103 iron atoms per particle) was estimated from the average blocking temperatures TBav, which is sensitive to the Fe:PVP ratio. For FeCl3:PVP preparations with Fe:PVP of 1:2, 1:6, and 1:20 TBav was 37, 10, and <4 K, respectively. A small proportion (<10%) of high‐spin ferrous iron centers was found in most samples. A third type of signal attributable to oxygen‐bridged ferric dimers was found in FeCl3–PVP preparations with Fe:PVP of 1:2 or 1:6 but not in Fe(No3)3–PVP samples. This species is probably [Cl3FeOFeCl3]2−. Interactions between the polymer and the various iron centers were weak.