Compounds related to organic Dirac electron systems (ODES) using linear gold(I) complex anions

Bis[bis(ethylenedithio)tetraselenafulvalene(0.5+)] dibromidoaurate(I) and its chloride analogue, (C10H8S4Se4)2[AuX2] or BETS2AuX2 (X = Cl and Br), were synthesized to examine their crystal and band structures. The crystal structures are new in that they have both structural features of different types of organic Dirac electron systems (ODES), i.e. α- and α'-type iodine-centred trihalide (IX2-) salts of BETS-related electron-donor molecules. The former often produces zero-gap semiconductors, while the latter is related to nodal-line semimetals, i.e. classes of ODES different from each other. The band structure calculation suggests that BETS2AuX2 are close to zero-gap semiconductors, indicating that the α-type structural feature governs the band structures in these salts. Although the dimensions and geometries of the constituents are close to each other between BETS2IX2 and BETS2AuX2, the strength of the BETS-anion interaction resulted in a difference in the crystal structures between the α- and α'-type molecular arrangements. Our findings show that the crystal and band structures are affected by the electronic states of the constituents sometimes more than one would expect based on their geometrical features.