Effects of halogen atom replacement on the structure and magnetic properties of a molecular crystal with supramolecular two-dimensional network mediated via sulfur’s σ-holes

Abstract

We prepared a novel Pt(mnt)2 (mnt = maleonitriledithiolato) anion radical salt (ethyl-4-iodothiazolium)2[Pt(mnt)2]3 (Pt-I) and investigated the structure and magnetic properties. The chemical composition indicated the existence of two negative charges (electrons) on three Pt(mnt)2 anions. The crystal structure of Pt-I contained a supramolecular rhombic motif mediated via sulfur’s σ-holes on the cation. The anions and cations formed a two-dimensional (2D) supramolecular network via noncovalent cation···anion interactions, where the arrangement of the ions was similar to that of an analogous complex (ethyl-4-bromothiazolium)2[Pt(mnt)2]3 (Pt-Br). On the other hand, the orientation of the cations and the stacking manner of the anions along the direction perpendicular to the 2D supramolecular network were different in Pt-I and Pt-Br. Such structural differences are attributed to the strength of the halogen bond, which is greater in iodine than in bromine. The comparison of the crystal structures between Pt-Br and Pt-I allowed us to estimate the contribution of the noncovalent interactions to the parent crystal structure. The magnetic investigations revealed the strong antiferromagnetic interaction (J/kB = −571 K for T > 280 K) between the spins on the trimerized anion. The interaction was greater in Pt-I than in Pt-Br, reflecting the stronger trimerization in Pt-I. These results suggest that sulfur-mediated chalcogen bonds can be robust enough to dominate the primary arrangement of molecules and the resulted physical properties, even in the presence of the other noncovalent intermolecular interactions or even upon the atomic replacements. Sulfur-based chalcogen bonds would be effective to realize desired structures and properties in molecular materials, while understanding the hierarchy of the noncovalent interactions operated in the crystal would be important for the precise crystal engineering.