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 (H2L): [Fe3(III)Fe2(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(III)O} 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(ox), 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.
Highlights
The pyridyl, amide and carboxylate functional groups are commonly used ligand donor sets in coordination chemistry as they offer a broad range of potential coordination modes to metal ions from across the periodic table.[1]
While the monodentate pyridyl group is limited in the way it might coordinate to a metal ion, the amide and carboxylate functionalities offer a vast array of coordination capacity ranging from mono- and multi-dentate modes to bridging multiple metal ions in the formation of clusters and polymers
Carboxylate ligands have been used as key building blocks in supramolecular chemistry due to the many potential binding modes available to the carboxylate group.[2]. These various binding modes are observed often within metallo-clusters that may range in size from two to an impressive eighty-four metal ions.[3]. Many of these carboxylate containing cluster-complexes behave as single-molecule magnets (SMMs).[4]
Summary
The pyridyl, amide and carboxylate functional groups are commonly used ligand donor sets in coordination chemistry as they offer a broad range of potential coordination modes to metal ions from across the periodic table.[1]. Carboxylate ligands have been used as key building blocks in supramolecular chemistry due to the many potential binding modes available to the carboxylate group.[2] These various binding modes are observed often within metallo-clusters that may range in size from two to an impressive eighty-four metal ions.[3] Many of these carboxylate containing cluster-complexes behave as single-molecule magnets (SMMs).[4] In these rapidly evolving areas of research, the search for new polydentate ligands is an ongoing challenge This has led increasingly to the design of ligands containing multiple functional groups that are capable of binding several metal ions.[5] In this respect, the N-(2-pyridyl)-3-carboxypropanamide ligand, H2L, is an excellent candidate for the synthesis of new polynuclear transition metal complexes, Fig. 1
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