Heterometallic Benzenehexathiolato Coordination Nanosheets: Periodic Structure Improves Crystallinity and Electrical Conductivity

Coordination nanosheets are an emerging class of 2D, bottom-up materials having fully pi-conjugated, planar, graphite-like structures with high electrical conductivities. Since their discovery, great effort has been devoted to expand the variety of coordination nanosheets; however, in most cases, their low crystallinity in thick films hampers practical device applications. In this study, mixtures of nickel and copper ions are employed to fabricate benzenehexathiolato (BHT)-based coordination nanosheet films, and serendipitously, it is found that this heterometallicity preferentially forms a structural phase with improved film crystallinity. Spectroscopic and scattering measurements provide evidence for a bilayer structure with in-plane periodic arrangement of copper and nickel ions with the NiCu2BHT formula. Compared with homometallic films, heterometallic films exhibit more crystalline microstructures with larger and more oriented grains, achieving higher electrical conductivities reaching metallic behaviors. Low dependency of Seebeck coefficient on the mixing ratio of nickel and copper ions supports that the large variation in the conductivity data is not caused by change in the intrinsic properties of the films. The findings open new pathways to improve crystallinity and to tune functional properties of 2D coordination nanosheets.

Automated summary

This study investigates the use of mixed nickel and copper ions to fabricate coordination nanosheet films based on benzenehexathiolato (BHT). It is found that this heterometallicity results in improved crystallinity and electrical conductivities in the films. Spectroscopic and scattering measurements confirm the formation of a bilayer structure with larger and more oriented grains. These findings open new opportunities for improving the functional properties of 2D coordination nanosheets.