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 T₁ in solid were measured on A₄[Pt₂I(P₂O₅H₂) ₄]·nH₂O (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 ³¹P resonance lines with chemical shifts close to those in the Pt³⁺ and Pt²⁺ 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 ³¹P T₁ in consistent with the above analysis. The observed spectra and T₁ depending on the cation size and the H₂O number suggest valence fluctuation due to spin jumps in and between Pt-Pt units sensitively influenced by crystal packings and hydrogen bonding.