Calixarene supported transition metal clusters
Taylor, Stephanie Merac
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This thesis describes a series of calix[n]arene polynuclear transition metal and lanthanide complexes. Calixarenes possess lower-rim polyphenolic pockets that are ideal for the complexation of various transition metal and lanthanide centres. Surprisingly however, with only a few exceptions, the coordination chemistry of p-tBucalix[ 4]arene (TBC), p-tBu-calixarene (TBC) and p-tBuhomotrioxacalix[ 3]arene (TBOC) with paramagnetic transition metal ions for the purpose of making and studying magnetically interesting molecules is unknown. Chapter two describes the reaction of TBC with manganese salts in the presence of an appropriate base (and in some cases co-ligand) resulting in the formation of a family of calixarene-supported [MnIII 2MnII 2] clusters (1-7) that behave as Single-Molecule Magnets (SMMs). These are: [MnIII 2MnII 2(OH)2(TBC)2(DMF)6]·2MeOH (1), [MnIII 2MnII 2(OH)2(TBC)2(DMF)4(H2O)2]·4MeOH·2DMF (2), [MnIII 2MnII 2(OH)2(TBC)2(DMF)6]·2.8MeOH (3), [MnIII 2MnII 2(OH)2(TBC)2(DMF)4(EtOH)(H2O)] (4), [MnIII 2MnII 2(OH)2(TBC)2(DMSO)6]·2MeOH·2DMSO (5) , [MnIII 2MnII 2(OH)2(TBC)2(DMSO)6] (6) and [MnIII 2MnII 2(OH)2(C)2(MeOH)6]·4MeOH (7). Variation in the alkyl groups present at the upper-rim of the cone allows for the expression of a degree of control over the self-assembly of these SMM building blocks, whilst retaining the general magnetic properties. The presence of various different ligands around the periphery of the magnetic core has some effect over the extended self-assembly of these SMMs. Chapter three describes how the combination of complementary cluster ligands; sodium phenylphosphinate and the N,O-chelate 2-(hydroxy-methyl)pyridine (hmpH) with TBC results in the formation of two new calixarene-supported clusters. This being an unusual [MnIIIMnII]2 dimer of dimers [MnIIIMnII(O2P(H)Ph)(DMF)2(MeOH)2]2 (8) and a ferromagnetic [Mn5] cage that displays the characteristic bonding modes of each support [MnIII 3MnII 2(OH)2(TBC)2(hmp)2(DMF)6](TBC-H)·xDMF ·xH2O (9). Chapter four details how using oxacalixarenes can tune the nature of the metal binding site, by introduction of ≥ 1 ethereal bridge. This results in Mn(II) rather than Mn(III) bonding in the phenolic pocket, and that these components self-assemble with additional Mn(II) and Mn(III) ions to form a [Mn10] supertetrahedron with an unusual oxidation state distribution, [MnII 6MnIII 4O4(TBOC)4(Cl)4(DMF)3]∙3.3H2O ∙ 1.5DMF (10). Chapter five introduces a family of lanthanide complexes formed using TBC. Variation in the experimental conditions employed in the reaction of TBC with lanthanide salts (LnX3) provides access to Ln1, Ln2, Ln4, Ln5, Ln6, Ln7 and Ln8 complexes, [Gd(TBC-2H)Cl(DMSO)4]·MeCN·H2O·(DMSO)2·hex (11), [CeIV 4(TBC-6H)2(μ3- O)2(DMF)4]·(DMF)5·hex·MeCN (12), [TbIII 5(TBC-5H)(μ4-O)(μ3- OH)4Cl(DMSO)8(H2O)3]Cl3·(DMSO)2(hex)2 (13), [CeIV 6(TBC-6H)2(μ4-O)2(μ2-OMe)4(μ2- O)2(DMF)4]·(DMF)6·hex (14), [Dy7(TBC-7H)(TBC-6H)(μ4-O)2(μ3-OH)2(μ2- OH)2(DMF)9]·(DMF)3 (15) and [Gd8(TBC-7H)2(μ4-CO3)2(μ5-CO3)2(μ2-HCO2)2(DMF)8] (16), with all polymetallic clusters containing the common bi-nuclear lanthanide fragment. Closer inspection of the structures of the polymetallic clusters reveals that all but one (Ln8) are in fact based on metal octahedra or the building blocks of octahedra.