Molecular squares with paramagnetic diruthenium corners: Synthetic and crystallographic challenges

The reaction of Ru₂(μ-O₂CMe)₄Cl with ∼2.5 equiv of HDAniF (HDAniF = N,N′-di(p-anisyl)-formamidine) in refluxing THF resulted in the synthesis of cis-Ru₂(μ-DAniF) ₂(μ-O₂CMe)₂Cl (1). This RU ₂₅₊-complex, which has two labile acetate groups occupying two equatorial cisoid positions, was used for the construction of discrete paramagnetic supramolecular arrays. Subsequent reactions of 1 with HO ₂C-CO₂H (oxalic acid) and 1,4-HO₂C-C ₆H₄-CO₂H (terephthalic acid) followed by recrystallization from 1,2-C₂H₄-Cl₂/hexanes solutions containing wet MeCN or 4-Bu^tpy (4-tert-butylpyridine) gave crystals of [{cis-Ru₂(μ-DAniF)₂Cl(H ₂O)}(μ-oxalate)]₄·MeCN·2(C ₆H₁₄)·12(H₂O) (2) and [{cis-Ru ₂(μ-DAniF)₂Cl_0.646(4-Bu^tpy) _1.354}(μ-terephthlate)]₄Cl _1.414·17(1,2-C₂H₄Cl ₂)·C₆H₁₄ (3), respectively. These are the first polygonal supramolecular assemblies consisting of paramagnetic M ₂ units at each apex, where M₂ = Ru₂₅₊. Compounds 2 and 3 have been structurally characterized, and their electrochemistry and magnetic properties have been studied. These studies have confirmed that oxalate linkers are better than the terephthalate linkers in effecting electronic and magnetic coupling.