The First Mixed Valence Radical Cation Salts of BEDT-TTF with the Photochromic Metal Mononitrosyl Complexes [RuNO X5] 2− ( X=Br, Cl) as Counterions

New bis(ethylenedithio)tetrathiafulvalene BEDT-TTF radical cation salts with the [RuNOX 5] 2− (X=Br, Cl) anions have been synthesized. The crystal structures of κ-(BEDT-TTF) 4[RuNOBr 5]·C 6H 5CN (1): a=8.747(2), b=12.088(1), c=17.300(2) Å, α=95.63(1), β=91.93(2), γ=94.79(2)°, V=1812.3(5) Å 3, P 1 , Z=1 and δ-(BEDT-TTF) 4[RuNOCl 5] 1.33 (2): a=6.721(1), b=15.016(2), c=35.386(3) Å, α=92.804(8), V=3567.0(8) Å 3, I2/ c, Z=2 have been determined. Their electronic band structures and transport properties have been studied. The radical cation salts κ-(BEDT-TTF) 4[RuNOCl 5]·C 6H 5CN (3) and δ-(BEDT-TTF) 4[RuNOBr 5] (4) have also been found to exist and are isostructural to 1 and 2, respectively. Evidence for commensurate and incommensurate structural modulations was found for 2 and 4, respectively. The crystals of 1 and 3 are semiconductors while those of 2 and 4 exhibit an M–I transition at 50 and 80 K, respectively.