Synthesis and characterisation of [(η-C5Me5)Ru(µ,η-C5Me5)Ru(η-C5Me5)]+[A]–; [A]–= TCNE, TCNQ, C3[C(CN)2]3. Crystal structure of the one-dimensional salt [(η-C5Me5)Ru(µ,η-C5Me5)Ru(η-C5Me5)]+[TCNE]–

Abstract

Charge-transfer salts [(η-Cp*)Ru(µ,η-Cp*)Ru(η-Cp*)]⁺[anion]^– Cp*= C₅Me₅; anion = tetracyanoethylene (TCNE, 2), 7,7,8,8-Tetracyano-p-quinodimethane (TCNQ, 3), or C₃[C(CN)₂]₃(4)] prepared from [(η-Cp*)Ru(µ,η-Cp*)Ru(η-Cp*)⁺ OTf^–(1)(OTf^–= trifluoromethanesulphonate) and M⁺[anion]^–(M⁺= Li⁺, NBu₄⁺) salts are described. Single-crystal X-ray studies show that 2 crystallises in the trigonal system, in the non-centrosymmetric space group R3m with a=b= 14.432(3)Å, c= 14.432(3)Å, α=β= 90°, γ= 120° with hexagonal indexing, V= 2603.3 ų, ρ_c= 1.41 g cm^–3, Z= 3, R= 0.0634 and R_w= 0.0715. The unit cell in 2 comprises alternating cations and anions aligned parallel to the crystallographic c axis. The cation has a multidecker structure with parallel Cp* rings and Ru–Cp˙_(centroid) distances of 1.826(7), 1.89(8), 1.826(7), and 1.828(9)Å. The diamagnetic [(η-Cp*)Ru(µ,η-Cp*)Ru(η-Cp*)]⁺ cation and the S= 1/2 [TCNE]^– radical anion lie on the crystallographic three-fold symmetry axis and consequently are highly disordered. The disordered anions possess local D_2h symmetry with C–CN, CN distances of 1.39(3) and 1.10(3)Å, respectively. For 2 and 3 the magnetic susceptibility obeys the Curie–Weiss expression χ=C/(T–θ), with µ_eff and θ values of 1.73 µ_B and 0.07° for 2 and 1.45 µ_B and –3.7° for 3.