Layered ferrimagnets constructed from charge-transferred paddlewheel [Ru2] units and TCNQ derivatives: the importance of interlayer translational distance in determining magnetic ground state

Abstract

A donor (D)/acceptor (A) assembly reaction using the paddlewheel-type diruthenium(II,II) complex [Ru₂(3,5-F₂PhCO₂)₄(THF)₂] (3,5-F₂PhCO₂⁻ = 3,5-difluorobenzoate; abbreviated hereafter as [Ru₂]) as D and 7,7,8,8-tetracyano-p-quinodimethane derivatives (TCNQR_x; 2,5-R-substituted TCNQ) as A in a DCM/TCE or DCE solvent system (DCM = dichloromethane, TCE = 1,1,2,2-tetrachloroethane, DCE = 1,2-dichloroethane) led to the formation of D₂A-type two-dimensional layered compounds [{Ru₂(3,5-F₂PhCO₂)₄}₂{TCNQR_x}]·nsolv (R_x = H₂ (1), R_x = Me₂, (2), and R_x = (OEt)₂ (3)). All the compounds had similar two-dimensional fishnet-type structures, where the two [Ru₂] units were fully coordinated with the four cyano groups of TCNQR_x. The compounds 1–3 were categorized as a one-electron transferred ionic state (1e-I) with D⁺–A⁻–D formulation (D⁺[Ru^II,III₂]⁺; A⁻TCNQR_x˙⁻). This subunit state formally derived a ferrimagnetically ordered state composed of up-spins with S = 1 for [Ru^II,II₂] and S = 3/2 for [Ru^II,III₂]⁺ and a down-spin of S = 1/2 for TCNQR_x˙⁻, with antiferromagnetic superexchange interactions in each layer. Eventually, 1–3 became three-dimensional ferrimagnets with Curie temperatures T_C = 93, 93, and 92 K, respectively, owing to the presence of interlayer ferromagnetic interactions. The interlayer translational distances (l₂) for the three compounds were 10.56, 10.54, and 10.84 Å, respectively, which agreed with the empirical prediction based on the threshold value of l₂ > 10.3 Å for a valid ferromagnetic interaction.