Magnetic Local Structures of Prussian-Blue Analogs: Hyperfine Coupling of the Cyanide Ions and the Coordination Water Molecules as Studied by Solid-State 13 C and D NMR

Abstract

Hyperfine coupling constant (HFCC) of a CN ligand must be sensitive to its coordination bond and local magnetic structures of Prussian-blue analogs. The HFCC of carbon atom of 13 CN ligand was determined to be m 23, m 39 and m 21 MHz for M=Li + (x=0.2, y=1.40), Na + (x=0.5, y=1.26) and Mg 2+ (x=0.2, y=1.32) of M x Co y [Fe( 13 CN) 6 ]zH 2 O in the high-spin state, respectively, from 13 C-NMR spectrum. A larger magnitude of the HFCC of the M=Na + complex suggests a unique local structure to exhibit a thermally induced spin phase transition around 240K. In the low-spin phase of the M=Na + complex, a 13 C-NMR signal showing a positive HFCC of Fe II (S=0)-CN-Co II (S=3/2) species was observed together with an intense signal of Fe II (S=0)-CN-Co III (S=0). Three kinds of crystal water molecules were distinguished by the magic angle spinning D-NMR for the deuterated M=Na + complex in the high-spin phase. Two of them interact with magnetic ions and are mobile even below the spin phase transition temperature. Co-Fe polycyanide magnetic local structures hyperfine coupling constant crystal water D MAS NMR 13 C-NMR