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

Maddock, Lewis Caradoc Huw and Borliovic, Ivana and McIntyre, Jamie and Kennedy, Alan R. and Aromi, Guilem and Hevia, Eva (2017) Synthetic, structural and magnetic implications of introducing 2,2’-dipyridylamide to sodium-ferrate complexes. Dalton Transactions. ISSN 1477-9234

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    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).