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

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Toyoda, Ryojun 
Fukui, Naoya 
Tjhe, Dionisius HL 
Selezneva, Ekaterina 
Maeda, Hiroaki 

Coordination nanosheets are an emerging class of two-dimensional, bottom-up materials having fully π-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, we find 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 NiCu2 BHT formula. Compared with homometallic films, heterometallic films exhibit more crystalline microstructures with larger and more oriented grains, achieving higher electric conductivities reaching metallic behaviours. 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. Our findings open new pathways to improve crystallinity and to tune functional properties of two-dimensional coordination nanosheets. This article is protected by copyright. All rights reserved.

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Adv Mater
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The Royal Society (nf121150)
Engineering and Physical Sciences Research Council (EP/P007767/1)
Engineering and Physical Sciences Research Council (EP/S030662/1)
EPSRC-JSPS core-to-core program (EP/S030662/1, JPJSCCA20190005)