SCIENTIFIC HIGHLIGHTS

Electron accumulative molecules: possible candidates for molecular electronics

Metallacarboranylviologen compounds are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way

A procedure leading to the formation of a B-N(aromatic) bond in an anionic sandwich metallabisdicarbollide cluster, [3,3’-M(1,2-C2B9H11)2]- (M= Co, Fe, [2]-), was developed. It consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B-N bond. This has paved the way to produce the metallacarboranylviologen [M(C2B9H11)(C2B9H10)-NC5H4-C5H4N-M’(C2B9H11)(C2B9H10)] (M=M’=Co, Fe and M= Co and M’=Fe) and semi(metallacarboranyl)viologen [3,3’–M(8-(NC5H4-C5H4N–1,2-C2B9H10)(1’,2’-C2B9H11)] (M=M’=Co, Fe) electron cumulative molecules with Fe, Co or a mix of both.

These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests, each Electron Transfer (ET) step has been assigned to specific fragments of the molecules. The molecules were carefully characterized and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the co-planarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side these metallacarboranylviologen compounds are much more soluble than C60 and its derivatives in the same or much related solvents, but most importantly that they offer a wider range of solvents of different nature.

The fact that these new compounds are very soluble in common organic solvents makes them possible candidates for molecular electronics and molecular materials in general. The electronic transfer from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility and easy processability can find important application in any area where ET is paramount.

Authors:
Ana B. Buades,1 Víctor Sanchez Arderiu,1 David Olid-Britos,1 Clara Viñas,1 Reijo Sillanpää,2 Matti Haukka,2 Xavier Fontrodona,3 Markos Paradinas,1 Carmen Ocal,1 and Francesc Teixidor1

Affiliations:
1 Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain
2 Dept. of Chemistry, University of Jyväskylä, Finland
3 Dept. de Química and Serveis Tècnics de Recerca, Universitat de Girona, Spain 

Publication:
Electron Accumulative Molecules.
Journal of the American Chemical Society  140, 2957−2970 (2018)

Figure:
Metallacarboranylviologen compounds, which are much more soluble than C60 and its derivatives, are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way.

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