Magnetostructural Correlations in Charge Transfer Ionic Chains Derived from Assembly of Paddlewheel Diruthenium(II, II) Complexes and 7,7,8,8-Tetracyano-p-quinodimethane Derivatives

The 1:1 assembly of an electron donor (D) and electron acceptor (A) results in a D⁺A^– charge transfer ion set, contingent upon the intrinsic highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels and packing structure. When these form charge-transfer one-dimensional (1d) chains, crystallization is often challenging, thereby complicating the systematic understanding of the correlation among their structure, charge state, and magnetism. Notably, only a few instances of ionic 1d chains formed by charge transfer between a paddlewheel diruthenium(II,II) complex ([Ru₂^II,II]) and an N,N′-dicyanoquinodiimine (DCNQI) or 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) derivative are known. In this study, we report two types of D⁺A^– ionic chains, [{Ru₂(5-X-2-OHArCO₂)₄}(TCNQF₂)]·n(solv) (5-X-2-OHArCO₂^– = 5-halogeno-2-hydroxybenzoate; TCNQF₂ = 2,5-difluorotetracyanoquinodimethane; X = Br, n(solv) = (anisole)(p-xylene), 1; X = Cl, n(solv) = 2(anisole), 2), which provide an alternating spin chain composed of S = 3/2 for [Ru₂^II,III]⁺ and S = 1/2 TCNQF₂^·–. Strong antiferromagnetic coupling with J ≈ −100 K was observed between two spin units in both compounds, forming ferrimagnetic chains. The correlation between the structure and exchange coupling of a series of [Ru₂^II,III]⁺–DCNQI^·–/TCNQ^·– ion chains was investigated. The findings of this study suggest that the Ru–N distance may be the most significant factor influencing the magnitude of the exchange interaction.