Polynuclear metal clusters using polyalkoxide ligands

We have investigated the use of calix[4]arenes in 3d and 3d/4f chemistry which produced a family of 7 new complexes. These are: [MnIII2MnII2(OH)2(TBC4)2(DMF)6] (1) , the analogous version with C4 (2). [MnIII4GdIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (3), [MnIII4TbIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (4), [MnIII4DyIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (5), [CuII9(OH)3(TBC4)3Cl2(DMSO)6](CuICl2)·DMSO (6·DMSO) (6) and [CuII9(OH)3(TBC4)3(NO3)2(DMSO)6](NO3)· DMSO (7·DMSO) (7). We continued with a series of Pseudo Metallocalix[6]arene planar disc complexes : [Ni7(OH)6(L1)6](NO3)2 (8), [Ni7(OH)6(L1)6](NO3)2.2MeOH (9), [Ni7(OH)6(L1)6](NO3)2.3MeNO2 (10), [Ni7(OH)6(L2)6](NO3)2.2MeCN (11), [Zn7(OH)6(L1)6](NO3)2.2MeOH.H2O (12) and [Zn7(OH)6(L1)6](NO3)2.3MeNO2 (13) and in the final part of this thesis we present a family of tetranuclear mixed valent Mn complexes using the tripodal ligand heedH2 : [MnII2MnIV2O2(heed)2(EtOH)6Br2]Br2 (14), [MnII2MnIV2O2(heed)2(H2O)2Cl4] (15), [MnII2MnIV2O2(heed)2(heedH2)2](ClO4)4 (16), [MnII2MnIV2O2(heed)2(MeCN)2(H2O)2(bpy)2](ClO4)4 (17), [MnII2MnIV2O2(heed)2(bpy)2Br4] (18); and the 2-D network of tetranuclear MnII/IV clusters {[MnII2MnIV2O2(heed)2(H2O)2(MeOH)2(dca)2]Br2}n (19). In total nineteen new complexes are reported. Studies of the magnetic properties show that 1 and 2 are SMM’s, whilst complex 3 is an excellent magnetic refrigerant for low-temperature applications and 4 and 5 behave as low-temperature molecular magnets

Enhancing SMM properties via axial distortion of Mn-3(III) clusters

Replacement of carboxylate and solvent with facially capping tripodal ligands enhances the single-molecule magnet (SMM) properties of [Mn-3(III)] triangles

Cluster Control in Oligouranyl Complexes of p-t-Butylcalix[8]arene

Formation of uranyl ion complexes of p-t-butylcalix[8]arene by reaction of the calixarene with [UO2(dmso)5]2+ in the presence of various bases leads to the crystallisation of solids with interestingly different stoichiometry, involving both di- and tri-uranate oligomers bound to the calixarene in anionic species. In all, the calixarene hexa-anion is present in a virtually identical conformation, suggesting that conformational preferences of the ligand must be a major factor controlling the form of the bound oxo-metal complex. Hydrogen bonding to the anions does not appear to be prominent even in the presence of protonated amines and this may explain the formation of some remarkable cation/solvent/simple anion clusters found within the lattices

[Mn(4)(III)Ln(4)(III)] Calix[4]arene Clusters as Enhanced Magnetic Coolers and Molecular Magnets

The use of methylene-bridged calix[4]arenes in 3d/4f chemistry produces a family of clusters of general formula [MnIII4LnIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (where C4 = calix[4]arene; Ln = Gd (1), Tb (2), Dy (3)). The molecular structure describes a square of LnIII ions housed within a square of MnIII ions. Magnetic studies reveal that 1 has a large number of molecular spin states that are populated even at the lowest investigated temperatures, while the ferromagnetic limit S = 22 is being approached only at the highest applied fields. This, combined with the high magnetic isotropy, makes the complex an excellent magnetic refrigerant for low-temperature applications. Replacement of the isotropic GdIII ions with the anisotropic TbIII and DyIII ions “switches” the magnetic properties of the cluster so that 2 and 3 behave as low-temperature molecular magnets, displaying slow relaxation of the magnetization.M.E. thanks the Spanish Ministry for Science and Innovation for grants MAT2009-13977-C03 and CSD2007- 00010.Peer Reviewe

Synthetic, structural, spectroscopic and theoretical study of a Mn(III)-Cu(II) dimer containing a Jahn-Teller compressed Mn ion

The heterobimetallic complex [Cu(II)Mn(III)(L)(2)(py)(4)](ClO4)center dot EtOH (1) built using the pro-ligand 2,2'-biphenol (LH2), contains a rare example of a Jahn-Teller compressed Mn(III) centre. Dc magnetic susceptibility measurements on 1 reveal a strong antiferromagnetic exchange between the Cu(II) and Mn(III) ions mediated through the phenolate O-atoms (J = -33.4 cm(-1)), with magnetisation measurements at low temperatures and high fields suggesting significant anisotropy. Simulations of high-field and high frequency powder EPR data suggest a single-ion anisotropy D-Mn(III) = +4.45 cm(-1). DFT calculations also yield an antiferromagnetic exchange for 1, though the magnitude is overestimated (J(DFT) = -71 cm(-1)). Calculations reveal that the antiferromagnetic interaction essentially stems from the Mn(d(x2-y2))-Cu(d(x2-y2)) interaction. The computed single-ion anisotropy and cluster anisotropy also correlates well with experiment. A larger cluster anisotropy for the S = 3/2 state compared to the single-ion anisotropy of Mn(III) is rationalised on the basis of orbital mixing and various contributions that arise due to the spin-orbit interaction