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 Å3, ρc= 1.41 g cm–3, Z= 3, R= 0.0634 and Rw= 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 D2h 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 µeff and θ values of 1.73 µB and 0.07° for 2 and 1.45 µB and –3.7° for 3.