Electronic Structure of the -(BEDT-TTF)2MHg(XCN)4 (M = Tl, K, NH4; X = S, Se) and Related Phases. Synthesis and Crystal Structure of the New Stable Organic Metal -(BEDT-TTF)2TlHg(Se1-xSxCN)4 (x = 0.125)

The synthesis, crystal structure, conductivity and electronic band structure of the new molecular metal a-(BEDT-TTF)2TlHg(Sei-~S~ CN)4 lx = 0.125) are reported. a-(BEDTTTF)2TlHg(Sei-~S~CN)4 lx = 0.125) is isostructural with ail other members of the family of o-(BEDT-TTF)2MHg(XCN)4 salts and is a stable metal down to very low temperatures. A general study of the electronic structure of ail structurally characterized a-(BEDT-TTF)2M Hg(XCN)4 salts as well as a-(BEDT-TTF)213, a-(BEDT-TTF)2IBr2 and o-(BEDT-TTF)4PtBr6 is also reported. Different aspects related to the electronic structure of these salts hke the stability of the metalhc state and the nature of the Fermi surface are discussed and correlated with the details of their crystal structures. The ongin of the different dimensionality of the carriers for the a-(BEDT-TTF)2MHg(XCN)4 salts Ii e., 1D electrons but 2D holes) , the metal to msulator transition m a-(BEDT-TTF)213 and the semiconducting behavior of a-(BEDT-TTF)2IBr2 and a-(BEDT-TTF)4PtBr6 are also discussed.