## 3 Results
### Hexacyanorrate Anions
[94] observed a band at 2111 cm\({}^{-1}\) was assigned to the CN stretching mode of hexacyanoferrate(III), and a second weak band at 2034 cm\({}^{-1}\) was attributed to the CN stretching mode of hexacyanoferrate(II), suggesting that a small amount of Fe\({}^{3+}\) was reduced to Fe\({}^{2+}\) in the LDH interlayer space. [PERSON], [PERSON], [PERSON] and [PERSON] [89] described two sharp bands at 2035 \(\pm\)1 cm\({}^{-1}\) assigned to the CN stretching mode of hexacyanoferrate(II) and at 2120-2086 cm\({}^{-1}\) attributed to the CN stretching mode of hexacyanoferrate(III) intercalated in LDH. [PERSON] and [PERSON] [31] detected the CN-stretching mode of hexacyanoferrate(II) and (III) at 2036 and 2112 cm\({}^{-1}\), respectively. In addition, they observed a band at 2080 cm\({}^{-1}\), which they attributed to the presence of free cyanide anions in the interlayer space of the LDH, indicating that the hexacyanoferrate(II,III) cyanide ligands can be replaced with  
Figure 9: XPS high-resolution scan of N 1s and C1s of LDH with Fe(CN)\({}_{6}\)\({}^{4-}\) as the interlayer anion. either water or hydroxyls. In addition, oxidation and ligand substitution of the hexacyanoferrate(II) were observed by Mossbauer spectroscopy. In contrast, [PERSON] et al. [95] attributed a band at 2030 cm\({}^{-1}\) when Fe(CN)\({}_{6}\)\({}^{3-}\) was incorporated in LDH to a CN\({}^{-}\) group in which the bond strength of CN\({}^{-}\) was weaker due to the interaction with the LDH hydroxide layer. The intensity of the band at 2030 cm\({}^{-1}\) was shown to increase upon aging. [PERSON], [PERSON], [PERSON] and [PERSON] [35] remarked that regardless of the nature of the starting hexacyanoferrate, two separate or overlapping bands were observed in all cases. Furthermore, the two bands are found closer to each other (maximum \(\Delta\)v = 46 cm\({}^{-1}\)) than for the pure potassium salts (\(\Delta\)v = 73 cm\({}^{-1}\)), indicating that the samples underwent redox processes resulting in a mixture of Fe\({}^{2+}\) and Fe\({}^{3+}\) species. They indicated that it is common knowledge from coordination chemistry that the exact band position of the \(\
u\)(CN) stretching mode for hexacyanoferrate(II) varies with the nature of the counter-cation. In the case of intercalated LDH, hydrogen bonding between interlayer water molecules or the LDH hydroxide layer hydroxyl groups and the cyano groups may likewise have an effect on the exact band position. [PERSON] et al. [96] observed the most intense band at 2118 cm\({}^{-1}\). In addition, a weak band was observed at 2042 cm\({}^{-1}\), while even weaker shoulders were detected at 2089 and 2060 cm\({}^{-1}\). The \(\
u_{\rm CN}\) band, at 2042 cm\({}^{-1}\), indicates a partial Fe\({}^{3+}\) to Fe\({}^{2+}\) reduction within the LDH interlayer space, similar to other studies. It is known that hexacyanoferrate anions are outer-sphere electron-transfer reductants or oxidants [97; 98], based upon which the origin of the two weaker bands at 2089 and 2060 cm\({}^{-1}\) can be assigned. Based on [PERSON] [99] the \(A_{1g}\), \(E_{g}\) and \(T_{1u}\)\(\
u_{\rm CN}\) modes required by the \(O_{h}\) point group for Fe(CN)\({}_{6}\)\({}^{4-}\) are found at 2094, 2062 and 2044 cm\({}^{-1}\) in aqueous solution. The first two modes are infrared-forbidden, but in the restricted interlayer space of the LDH, they can become partially activated due to a decrease in symmetry, resulting in the two weak bands at 2089 and 2060 cm\({}^{-1}\), respectively. If grafting had happened (if the calculated interlayer space height was smaller than the size of the Fe(CN)\({}_{6}\)\({}^{4-}\) anion along the \(C_{3}\) axis), the decrease in symmetry would have been much more dramatic, and the infrared spectrum much more complicated. [PERSON] et al. [100] and [PERSON] et al. [101] studied oriented samples of hexacyanoferrate intercalated LDH and compared those to randomly oriented samples.