New crystal packing arrangements in radical cation salts of BEDT-TTF with [Cr(NCS)6]3− and [Cr(NCS)5(NH3)]2−

Andrew C Brooks,Lee Martin,Peter Day,William Clegg,Ross W Harrington,John D Wallis

doi:10.1016/j.poly.2015.07.013

Abstract

BEDT-TTF forms three packing arrangement styles in its radical cation salts with [Cr(NCS)6]3− in two of which two trans-oriented isothiocyanate ligands penetrate the BEDT-TTF layers either at the point where a solvent (nitrobenzene) is incorporated in a stack of donors or by four donor molecules forming a “tube” motif to accept a ligand at each end along with a small solvent molecule in between (acetonitrile). The [Cr(NCS)5NH3]2− ion forms a related crystal packing arrangement with BEDT-TTF with a reduction in the number of “tube” motifs needed to accept an isothiocyanate ligand.

Highlights

Radical cation salts provide the opportunity to combine together in the same crystal lattice multiple physical properties which may not usually be found together
The need to accommodate an octahedral ion with side arms three atoms long in salts of BEDT-TTF with [Cr(NCS)6]3À can be solved in several ways
Either two ligand side arms are inserted into BEDT-TTF/aromatic solvent stacks at the points where the smaller solvent molecules occur, or four BEDT-TTF molecules form a channel to incorporate the side arms at either end, with the central space filled by solvent

Summary

Introduction

Radical cation salts provide the opportunity to combine together in the same crystal lattice multiple physical properties which may not usually be found together. The influence of chirality on the electromagnetic properties of radical cation salts is very topical [15,16,17,18], and electrocrystallisation of BEDT-TTF with the racemic [Cr(C2O4)3]3À trianion from a chiral electrolyte has produced a family of semiconducting salts of the formula (BEDT-TTF)3AM(C2O4).Guest (A = Na, NH4; M = Cr, Al) containing a single enantiomer of [M(C2O4)3]3À [19,20,21,22]. Our results will be set in the context of several known phases containing BEDT-TTF and [Cr(NCS)6]3À [29,30,31], and the reinterpretation of a phase containing [Cr(NCS)5NH3]2À which had been communicated [32] to the Cambridge Structural Database [33]

Discussion

Conclusion

Experimental