| Abstract
| - Crystal structures and magnetic properties were determined for two novel compounds, [1-(4‘-iodobenzyl)pyridinium][M(mnt)2] (mnt2- = maleonitriledithiolate; M = Ni (1) or Cu (2)). At room temperature, singlecrystals of 1 and 2 were isostructural, featuring the formation of segregated columnar structures with regularstacks of cations and anions. For crystal 1, a magnetic transition was observed at ∼120 K; furthermore, itsmagnetic behavior was consistent with that of a regular Heisenberg antiferromagnetic (AFM) chain of S =1/2 in the high-temperature phase (HT phase) and that of a spin-gap system in the low-temperature phase (LTphase). Such a phenomenon is similar to the spin-Peierls transition. However, the crystal structure of 1 in theLT phase at 100 K revealed that its structural transition is associated with the magnetic transition. Becausecrystal 2 (S = 0) did not exhibit a structural transition, the structural transition of 1 is driven by spin−latticeinteraction.
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