Synthetic, structural and magnetic implications of introducing 2,2′-dipyridylamide to sodium-ferrate complexes

Abstract

Using a transamination approach to access novel Fe(II) complexes, this study presents the synthesis, X-ray crystallographic and magnetic characterisation of a series of new iron complexes containing the multifunctional 2,2-dipyridylamide (DPA) ligand using iron bis(amide) [{Fe(HMDS)₂}₂] and sodium ferrate [{NaFe(HMDS)₃}_∞] (1) as precursors (HMDS = 1,1,1,3,3,3-hexamethyldisilazide). Reactions of DPA(H) with 1 show exceptionally good stoichiometric control, allowing access to heteroleptic [(THF)₂·NaFe(DPA)(HMDS)₂] (3) and homoleptic [{THF·NaFe(DPA)₃}_∞] (4) by using 1 and 3 equivalents of DPA(H), respectively. Linking this methodology and co-complexation, which is a more widely used approach to prepare heterobimetallic complexes, 3 can also be prepared by combining NaHMDS with heteroleptic [{Fe(DPA)(HMDS)}₂] (2). In turn, 2 has been also synthesised and structurally defined by reacting [{Fe(HMDS)₂}₂] with two equivalents of DPA(H). Structural studies demonstrate the coordination flexibility of the N-bridged bis(heterocycle) ligand DPA, with 2 and 3 exhibiting discrete monomeric motifs, whereas 4 displays a much more intricate supramolecular structure, with one of its DPA ligands coordinating in an anti/anti fashion (as opposed to 2 and 3 where DPA shows a syn/syn conformation), which facilitates propagation of the structure via its central amido N. Magnetic studies confirmed the high-spin electron configuration of the iron(II) centres in all three compounds and revealed the existence of weak ferromagnetic interactions in dinuclear compound 2 (J = 1.01 cm⁻¹).