Optical and magnetic properties of K[M{S2C2(CN)2}2]·H2O (M = Ni, Pt, or Au)

Abstract

The solid-state spectra of two series of [M(mnt)₂]^–{mnt =[S₂C₂(CN)₂]^2–, M = Ni, Pt, or Au} monoanion salts of K^– and [NEt₄]⁺ have been recorded. The polarized absorption spectrum of K[Ni(mnt)₂]·H₂O is characterized by a strong band at 6 700 cm^–1 assigned to the intermolecular charge-transfer (c.t.) transition along the stacking direction, which is the first direct evidence of the one-dimensional character of its electronic structure. On the contrary, the polarized reflectance spectra of [Net₄][M(mnt)₂](M = Ni or Pt) are characterized by reflectance peaks at 7 200 cm^–1, corresponding to the intermolecular c.t. transition within the dimer. The magnetic susceptibilities of K[M(mnt)₂]·H₂O (M = Ni or Pt) are also described. The behaviour of the platinum complex can be explained by the alternating antiferromagnetic S=½ Heisenberg chain model with the alternation parameter α= 0.9 and the exchange parameter 2|J|= 640 cm^–1, which is consistent with its weakly dimerized stack structure.