Syntheses, structure, and magnetic properties of heteronuclear Cu(ii)4Fe(iii)4 cluster and Cu(ii)8 bimetallacycles

Abstract

The compartmental Schiff base ligands N,N′-ethylenebis(3-hydroxysalicylidene) (H₄L) and N,N′-propylenebis(3-hydroxysalicylidene) (H₄L′) have been employed in the synthesis of a cyclic tetranuclear Cu(II) complex [Cu₄(L′)₂(MeOH)₃(H₂O)]·[Cu₄(L′)₂(MeOH)₃] (1), a novel octanuclear Cu(II) complex [Cu₈(L–L)₂(H₂O)₄(μ₂-H₂O)]·3DMF·3H₂O (2) and a hetero-octanuclear Cu(II)–Fe(III) complex [Cu₄Fe₄(L)₄(H₂O)₃(μ₃-O)₂]·3DMF·3H₂O (3). During the formation of the Cu₈ complex (2), a new bis-Schiff base ligand (L–L)⁸⁻ forms via the ortho–para C–C coupling of two H₄L ligands. The bicyclic complex (2) is comprised of two cyclic Cu₄ units that are similar to that of complex 1. In the Cu₄ unit, the alternate Cu(II) ions are singly bridged by phenoxo groups. The three complexes display overall antiferromagnetic coupling, and the Cu(II)–Cu(II) magnetic coupling constant falls in the range −117.2 to −473.6 cm⁻¹ for complexes 1 and 2 corresponding to the bridging Cu–O_phenoxide–Cu bond angles of 124.3–131.0°.