Perylene salts with tetrahalogenoferrate( III ) anions. Synthesis, crystal structure of [(C 20 H 12 ) 3 ][FeCl 4 ] and characterisation

Two new perylene (C20H12) salts [(C20H12)3][FeCl4]1 and [(C20H12)3][FeBr4]2 have been synthesised and characterised. Compound 1 crystallises in the triclinic system, space group P, with a= 12.8393(11), b= 14.1333(11), c= 14.8391(14)Å, α= 91.680(7), β= 113.114(7), γ= 115.119(7) and Z= 2, and its structure consists of tetramerised stacks of perylenes flanked by additional pseudoorthogonal perylene molecules and tetrachloroferrate(III) anions. Resistivity and thermopower measurements characterise [(C20H12)3][FeCl4]1 as a semiconductor with a room-temperature conductivity σ≈ 0.17 S cm–1 with an activation energy of 0.12 eV. The magnetic behaviour of both compounds is dominated by the contribution of the paramagnetic iron(III) centres. Magnetic susceptibility data in the temperature range 3–300 K were fitted to the equation for a binuclear S=S′= 5/2 interaction, with J/k=–1.26(1) K and g= 2.022(4) for 1 and J/k=–3.72(4) K and g= 2.03(2) for 2.