Paramagnetic precursors for supramolecular assemblies: Selective syntheses, crystal structures, and electrochemical and magnetic properties of Ru ₂(O₂CMe)_4-n(formamidinate)_nCl complexes, n = 1-4

Reactions of Ru₂(O₂CMe)₄Cl with two formamidines, HDXyl_2,6F = N,N′^2,6-di(2,6-xylyl) formamidine and HDAniF = N, N′-di(p-anisyl)formamidine, have been investigated with the idea of synthesizing compounds with a mixed set of ligands having different labilities to be used as precursors of paramagnetic, higher-order assemblies. Depending on the formamidine and the reaction conditions, several Ru₂⁵⁺ compounds of the type Ru ₂(O₂CMe)_4-n(DArF)nCl (DArF = anion of an N,N′-diarylformamidine) have been isolated. With the bulky formamidine HXyl^2,6F, the compounds Ru₂(O₂CMe) ₃(DXyl^2,6F)Cl (1) and trans-Ru₂(O ₂CMe)₂(DXyl^2,6F)₂Cl (2) were obtained. From reactions with appropriate amounts of HDAniF in THF and in the presence of NEt₃ and LiCl, complexes of the general type Ru ₂(O₂CMe)_4-n(DArF)_nCl (n = 1-4) were selectively obtained. For n = 2, only the cis isomer was obtained. The choice of solvent in reactions of Ru2(O₂CMe)₄Cl and HDAniF is of great importance. Toluene favored the formation of the fully substituted Ru ₂⁵⁺ complex Ru₂(DAniF)₄Cl (3), whereas MeOH resulted in a disproportionation reaction that gave the edge-sharing bioctahedral Ru³⁺Ru³⁺ complex [trans- Ru ₂(μ-OMe)₂(μ-O₂CMe)₂(HDAniF) ₄]Cl₂ (6) and the Ru₂⁴⁺ complex Ru₂(DAniF)₄ (7). Complexes 6 and 7 with an Ru ₂⁶⁺ and Ru₂⁴⁺ core, respectively, are diamagnetic, whereas all Ru₂⁵⁺ complexes are paramagnetic with σ²π⁴δ² (π*δ*)³ ground-state electronic configurations and large zero-field splitting contributions. All compounds show rich and complex electrochemical behavior.