Crystal architecture of the cocrystalline salt [Ru(η5-C5H5)(η6-trans-PhCHCHPh)][PF6]·0.5trans-PhCHCHPh and the reversible order–disorder phase transition in [Ru(η5-C5H5)(η6-C6H6)][PF6]

Abstract

The crystal architecture, stability and behaviour with temperature of the hexafluorophosphate salts [Ru(η⁵-C₅H₅)(η⁶-arene)]⁺ (arene = benzene 1 or trans-stilbene 2) have been investigated by variable temperature X-ray diffraction and differential scanning calorimetry. Compound 1 shows a reversible high temperature phase transition to a semi-disordered phase at 332 K. It is pseudo-isomorphous with [Cr(η⁶-C₆H₆)₂][PF₆] and with the room temperature form of [M(η⁵-C₅H₅)₂][PF₆] (M = Co or Fe), the latter species also undergoing reversible phase transitions. Crystalline 2 has been characterised in its cocrystallised form [Ru(η⁵-C₅H₅)(η⁶-trans-PhCHCHPh)]- [PF₆]·0.5trans-PhCHCHPh. The trans-stilbene molecules fill in the voids formed in the packing when the small [PF₆]^– anions assemble with the large and asymmetric [Ru(η⁵-C₅H₅)(η⁶-trans-PhCHCHPh)]⁺ cations. The role of charge assisted C–H^(δ+)· · ·F^(δ–) interactions is discussed.