AbstractThe chemical substitution of a transition metal (M) is an effective method to improve the functionality of materials. In order to design the highly functional materials, we first have to know the local structure and electronic state around the substituted element. Here, we systematically investigated the local structure and electronic state of the host (M_h) and guest (M_g) transition metals in metal-hexacyanoferrate (M-HCF), Na _x (M_h, M_g)[Fe(CN)₆] _y (1.40 < x < 1.60 and 0.85 < y < 0.90), by means of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analyses. The EXAFS and XANES analyses revealed that the local structure and electronic state around M_g are essentially the same as those in the pure compound, i.e, M_g-HCF. Such an invariant nature of M_g in M-HCF is in sharp contrast with that in layered oxide, in which the M_g valence changes so that local M_g-O distance (d _M-O^g) approaches the M_h-O distance (d _M-O^h).