13C NMR spectra at room temperature and the temperature dependences of 1H T1 in the solid state were measured in [Ni 1-xPdxX(chxn)2]X2 (X: Cl, Br; chxn: 1R,2R-cyclohexanediamine; 0.0 < x < 1.0), where antiferromagnetically coupled paramagnetic -X-Ni3+-X-Ni3+-X- chains were formed at x = 0.00, while the mixed-valence -X-Pd2+-X-Pd4+-X- state was made at x = 1.00. 13C signals at α-carbons in chxn coordinating to Pd atoms showed a doublet assignable to Pd2+ and Pd4+ in x = 1.00, while, with a slight decrease of x from 1.00, a clear broadening and a shift to low-field of signals, indicating conversion into the averaged Pd3+ state, were observed. This can be explained by the fluctuation of the Pd valency caused by neighboring paramagnetic Ni 3+ sites introduced in small amounts in the 1-D chain. The x dependences of the chemical shifts of β- and γ-carbons are also attributable to the effect from a partial mixing of the paramagnetic Pd 3+ sites. The values of 1H T1 and its temperature dependence observed in the ranges of 100-300 K and x < 0.13 for [Ni1-xPdxBr(chxn)2]Br2 could be explained by a model of strong exchange interactions between Ni3+ and Pd3+ as well as Ni3+ sites. Gradual changes in the T 1 value and slope with increasing x from 0.00 to 0.93 are attributable to the variation of the exchange interaction value, which depends upon the number of Ni-Ni pairs.
ASJC Scopus subject areas
- 化学 (全般)