Electronic State of Iron Complexes in the Interlayer of Hydrotalcite-Like Materials

Infrared and Mössbauer spectroscopic studies were made on hydrotalcite-like materials, Mg 6 Al 2 (OH) 16 (NO 3 ) 2 ·4H 2 O, anion exchanged in aqueous solution of K 3 Fe(CN) 6 , K 4 Fe(CN) 6 ·3H 2 O, or Na 2 Fe(CN) 5 NO·2H 2 O. The material anion-exchanged in aqueous solution of K 3 Fe(CN) 6 gave infrared (IR) absorption bands at 2120 and 2040 cm -1 in the C≡N stretching region, suggesting that part of the ferrate(III) complex was reduced to ferrate(II) complex on the intercalation chiefly because pure K 3 Fe(III)(CN) 6 and K 4 Fe(II)(CN) 6 ·3H 2 O gives bands at 2120 and 2040 cm -1 , respectively. On the intercalation of Fe(CN) 6 4- , no change in the oxidation state of iron was observed. These features were confirmed by Mössbauer spectroscopy. In the IR spectra of material anion-exchanged in aqueous solution of Na 2 Fe(CN) 5 NO·2H 2 O, the intensity of bands due to N≡O (1940 cm -1 ) and C≡N stretching was much less than that observed for Na 2 Fe(CN) 5 NO·2H 2 O, indicating that most of N≡O ligand was eliminated during the intercalation. Four bands were observed in the C≡N stretching region: a band at 2143 cm -1 was assigned to C≡N groups in Fe(CN) 5 NO 2- ; a band at 2120 cm -1 was tentatively assigned to Fe(CN) 5 H 2 O 2- ; bands at 2040–2050 cm -1 were assigned to Fe(CN) 5 H 2 O 3- .