Use of Halogen Bonding in a Molecular Solid Solution to Simultaneously Control Spin and Charge

Halogen-bonding interactions have attracted increasing attention in various fields of molecular science. Here we report the first comprehensive study of halogen-bonding-utilized solid solution for simultaneous control of multifunctional properties. A series of anion-mixed molecular conductors (DIETSe)2MBr4xCl4(1–x) [DIETSe = diiodo­(ethylenedithio)­tetraselenafulvalene; M = Fe, Ga; 0 x T > 0.3 K, H x gradually suppresses a metal–insulator transition attributed to the nesting instability of the quasi-one-dimensional Fermi surfaces. It suggests the dimensionality of π electrons is extended by increasing the anion size, which is opposite of the typical effect of chemical pressure. We found that the “negative” chemical pressure is associated with the characteristic halogen-bonding network. Br substitution also enhances the antiferromagnetic (AF) ordering of d-electron spins in the Fe salts, as indicated by the Néel temperature, AF phase boundary field, and saturation field. Furthermore, we observed hysteresis in both magnetization and resistivity only in halogen-mixed salts at very low temperatures, indicating simultaneous spin and charge manipulation by alloying.