New Organic Metals Based on BDH-TTP Radical Cation Salts with the Photochromic Nitroprusside Anion [FeNO(CN)5]2–

Three new 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) radical cation salts with the photochromic nitroprusside anion have been synthesized: kappa-(BDH-TTP)(4)[FeNO(CN)(5)].NB (1), kappa-(BDH-TTP)(4)[FeNO(CN)(5)] (2), and (BDH-TTP)(2)[FeNO(CN)(5)] (3). The salts were characterized by single-crystal X-ray diffraction, electrical resistance measurements, and electronic band structure calculations. The crystals of 1 and 2 have a layered structure in which the BDH-TTP layers of kappa-type alternate with anionic sheets. Solvent (nitrobenzene) molecules are also involved in the composition of the anion sheet of 1. The crystals of 1 have triclinic symmetry and two crystallographically independent BDH-TTP radical cations in the unit cell, while there is only one independent radical cation in the monoclinic structure of 2. The salts 1 and 2 are stable quasi-2D metals down to 4.2 K, while 3, with full charge transfer, is a semiconductor with low conductivity at room temperature. It is suggested that the kappa-type layers of BDH-TTF are more robust than those of BEDT-TTF and its derivatives and the consequences for the electronic structure are discussed.