Anion conformation and physical properties in BETS salts with the nitroprusside anion and its related ruthenium halide (X = Cl, Br) mononitrosyl complexes: theta-(BETS)(4)[Fe(CN)(5)NO], (BETS)(2)[RuBr5NO], and (BETS)(2)[RuCl5NO]

theta-(BETS)(4)[Fe(CN)(5)NO] (1), (BETS)(2)[RuBr5NO] (2), and (BETS)(2)[RuC l5NO] (3) [BETS = bis(ethylenedithio)tetraselenafulvalene] have been prepar ed by electrocrystallisation of BETS using [Fe(CN)(5)NO](2-) or [RuX5NO](2- ), X = Cl or Br, as supporting electrolytes and 1,1,2-TCE/ethanol (10 vol%) for 1, nitrobenzene/1,2-DCE (40 vol%)/ethanol (10 vol%) for 2, and benzoni trile/ethanol (10%.) solutions for 3 as solvents. Compound 1 exhibits a met allic behaviour down to 40 K, 2 behaves as a semiconductor and 3 as an insu lator. The crystal structures of 1, 2, and 3 were determined by X-ray diffr action methods. BETS molecules in 1 crystallised in a theta -type mode. By contrast, the crystal structures of 2 and 3 show a packing of BETS molecule s consisting of slipped, stacked (BETS)2 dimers. The dimerisation is much s tronger in 3 than in 2. The physical behaviours of the three phases were in vestigated by means of molecular and band structure calculations and are sh own to be directly related to the [MX5NO] (M = Fe, X CN; M = Ru, X = Cl, Br ) structural conformations.