Synthesis, structural and magnetic characterisation of iron(ii/iii), cobalt(ii) and copper(ii) cluster complexes of the polytopic ligand: N-(2-pyridyl)-3-carboxypropanamide

Abstract

Herein we describe the synthesis, structural and magnetic characterisation of three transition metal cluster complexes that feature the polytopic ligand N-(2-pyridyl)-3-carboxypropanamide (H₂222L): [Fe₃^IIIFe₂^II(HL)₆(O)(H₂O)₃][ClO₄]₅·3MeCN·4H₂O, 1, [Co₈(HL)₈(O)(OH)₄(MeOH)₃(H₂O)]-[ClO₄]₃·5MeOH·2H₂O, 2, and [Cu₆(L_ox)₄(MeOH)(H₂O)₃]·MeOH, 3. Complex 1 is a mixed valence penta-nuclear iron cluster containing the archetypal {Fe₃^IIIO} triangular basic carboxylate cluster at its core, with two Fe(II) ions above and below the core coordinated to three bidentate pyridyl-amide groups. The structure of the octanuclear Co(II) complex, 2, is based upon a central Co₄ square with the remaining four Co(II) centres at the ‘wing-tips’ of the complex. The cluster core is replete with bridging oxide, hydroxide and carboxylate groups. Cluster 3 contains an oxidised derivative of the ligand, L_oxox, generated in situ through hydroxylation of an α-carbon atom. This hexanuclear cluster has a ‘barrel-like’ core and contains Cu(II) ions in both square planar and square-based pyramidal geometries. Bridging between Cu(II) centres is furnished by alkoxide and carboxylate groups. Magnetic studies on 1–3 reveals dominant antiferro-magnetic interactions for 1 and 2, leading to small non-zero spin ground states, while 3 shows ferro-magnetic exchange between the Cu(II) centres to give an S = 3 spin ground state.