Metamagnetism with TN = 97 K in a layered assembly of paddlewheel [Ru2] units and TCNQ: an empirical rule for interlayer distances determining the magnetic ground state

Abstract

A donor (D)/acceptor (A) assembly reaction of the paddlewheel-type diruthenium(II,II) complex [Ru₂(m-ClPhCO₂)₄(THF)₂] (m-ClPhCO₂⁻ = meta-chlorobenzoate; abbreviated hereafter as [Ru₂]) with 2,5-dimethoxy-7,7,8,8-tetracyano-p-quinodimethane (TCNQ(MeO)₂) in a dichloromethane (DCM)/1,1,2,2-tetrachloroethane (TCE) solvent system led to the formation of a two-dimensional layered D₂A compound with crystallization solvents located between layers: [{Ru₂(m-ClPhCO₂)₄}₂{TCNQ(MeO)₂}]·3.3DCM·2TCE (1). Compound 1 undergoes an intra-lattice one-electron transfer to form a charge-distributed state with the formula [{Ru^II,III₂}⁺–TCNQ˙⁻–{Ru^II,II₂}] with intra-layer ferrimagnetic spin ordering through dπ*–pπ* orbital overlap that results in ferrimagnetic arrangement with antiferromagnetic interactions over heterospins of S = 1 for [Ru^II,II₂] and S = 3/2 for [Ru^II,III₂] via S = 1/2 for TCNQ˙⁻. Consequently, because of the presence of interlayer antiferromagnetic interactions, 1 has an antiferromagnetic ground state with T_N = 97 K. On applying a field of less than 0.5 T, a spin flip is induced, yielding a field-induced ferrimagnet (a type of metamagnet) with a large coercive field of 1.2 T at 1.8 K. Compound 1 has interlayer translational (i.e., interlayer [Ru₂]⋯[Ru₂] or TCNQ⋯TCNQ distance) (l₂) and interlayer vertical (l₁) distances of 10.30 and 9.82 Å, respectively. By comparison of the magnetostructural correlations of this type of layered magnet, this class of antiferromagnets, including 1, reveal a trend of having l₂ ≤ 10.3 Å.