A highly methanol-selective vapochromic response has been realized in a Ni -quinonoid complex, [Ni(HL ) ] (H L =4-methylamino-6-methyliminio-3-oxocyclohexa-1,4-dien-1-olate) which exhibits a reversible structural transformation including a coordination geometrical change between the square-planar and octahedral structure by the selective uptake of methanol vapor. This was accompanied by a remarkable color change between purple and orange, as well as temperature-robust spin-state switching in the solid state under ambient conditions. It is remarkable that the properties are derived by the fine structural modification of the quinonoid ligand such as methyl or ethyl analogues. Such a system has high potential for applications in memory devices as well as chemical sensors and smart responsive materials.

To verify the effect of geometrical frustration, we artificially distort the triangular lattice of quasi-two-dimensional organic conductor κ-(BEDT-TTF)2Cu2(CN)3 [BEDT-TTF: bis(ethylenedithio)terathiofulvalene] by analogous-molecular substitution and apply 13 C NMR of bulk and substituted sites, electric conductivity, and static magnetic susceptibility measurements.The results indicate that the magnetic characteristics of the substituted sample are quantitatively similar to those of the pure sample. Moreover the magnetic characteristics at the substituted sites are also the same as in the bulk. These results suggest that the observed magnetic properties may not be due to the geometrical frustration but the importance of disorder.

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A highly methanol‐selective vapochromic response has been realized in a NiII‐quinonoid complex, [Ni(HLMe)2] (H2LMe=4‐methylamino‐6‐methyliminio‐3‐oxocyclohexa‐1,4‐dien‐1‐olate) which exhibits a reversible structural transformation including a coordination geometrical change between the square‐planar and octahedral structure by the selective uptake of methanol vapor. This was accompanied by a remarkable color change between purple and orange, as well as temperature‐robust spin‐state switching in the solid state under ambient conditions. It is remarkable that the properties are derived by the fine structural modification of the quinonoid ligand such as methyl or ethyl analogues. Such a system has high potential for applications in memory devices as well as chemical sensors and smart responsive materials.