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 0.3 K, H < 35 T) using the single crystals demonstrated simultaneous control of both spin and charge degrees of freedom. The increase in Br content 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”...