Valence structure and magnetic interaction in MMX-type 1D complexes, A4[Pt2I(P2O5H2)4]·nH2O, studied by 31P solid NMR

31P MAS-NMR spectra and spin-lattice relaxation time T 1 in solid were measured on A 4 [Pt 2 I(P 2 O 5 H 2 ) 4 ].nH 2 O (A: Cs, Rb, K, Na and Li). Continuous spectrum changes in both line and splitting widths were observed with changing the cation size and the number of crystalline water. Complexes with A: Cs (n=0) and Rb (n=2) afforded two kinds of 31 P resonance lines with chemical shifts close to those in the Pt 3+ and Pt 2+ monomer complexes indicating a mixed valence structure. On the other hand, complexes with A: Na (n=2) and Li (n=4) yielded a broad single line suggesting the formation of paramagnetic Pt sites with an averaged valence of Pt 2.5+ . An analogous continuous change was observed in 31 P T 1 in consistent with the above analysis. The observed spectra and T 1 depending on the cation size and the H 2 O number suggest valence fluctuation due to spin jumps in and between Pt-Pt units sensitively influenced by crystal packings and hydrogen bonding.