Rebecca O. Fuller

Lanthanoid “Bottlebrush” Clusters: Remarkably Elongated Metal–Oxo Core Structures with Controllable Lengths

Large metal-oxo clusters consistently assume spherical or regular polyhedral morphologies rather than high-aspect-ratio structures. Access to elongated core structures has now been achieved by the reaction of lanthanoid salts with a tetrazole-functionalized calixarene in the presence of a simple carboxylate co-ligand. The resulting Ln19 and Ln12 clusters are constructed from apex-fused Ln5O6 trigonal bipyramids and are formed consistently under a range of reaction conditions and reagent ratios. Altering the carboxylate co-ligand structure reliably controls the cluster length, giving access to a new class of rod-like clusters of variable length.

The use of preformed nanoparticles in the production of heterogeneous catalysts

Preformed iron oxide nanoparticles have been successfully assembled onto alumina and MCM-41 support materials. The particles are found to disperse evenly over the surface of the silicate; however, in the case of the alumina we find that in addition to areas of even distribution there is also some clustering of the particles. The materials are stable under heat treatment, with no signs of further aggregation during calcination. We investigate the reducibility of the materials through H2-TPR studies and we find that the particles are reducible around 500-550°C. The reduction process is complete at temperatures where MCM-41 can undergo degradation, supporting that the alumina based materials are more suited to the multiple base oxidation reduction steps in the catalytic cycle.

Supramolecular interactions between hexabromoethane and cyclopentadienyl ruthenium bromides: Halogen bonding or electrostatic organisation?

The interaction between hexabromoethane and [CpRu(CO)2Br] (Cp = (η-C5H5), results in the deposition of two different isostoichiometric co-crystals, 2[CpRu(CO)2Br]·C2Br6, one crystallising in space group P (Z = 1) and the other in P21/n (Z = 4). These were produced in the reaction of HCBr3 and [(CpRu(CO)2)2] under indoor illumination, following a slight modification of the literature procedure. The origin of the hexabromoethane is as yet unknown but it appears to have been formed in the reaction rather than being an impurity in the bromoform. We have analysed the structures using the Hirshfeld surface approach and electrostatic potentials, supported by DFT theoretical calculations to better define the nature of intermolecular interactions in the solid state. The results indicate that the most significant interactions within both crystal forms arise not from the closest van der Waals contacts but, rather, from more distant interactions between the unsymmetrical electron distributions about the bromine atoms in the solvate and substrate molecules.

The modification of M41S materials: addition of metal clusters and nanoparticles

The incorporation of various molecular metal clusters, with well defined stoichiometry, into M41S materials has been investigated. The grafting of simple metal clusters, such as [Ru3(CO)12] and [PPN]2[Fe4(CO)13], and the larger, and in one instance, bimetallic, clusters [(dppe)2Cu][Cu6Fe4(CO)16] and [PPh4][Ru10(μ6-C)(μ-H)(CO)24] has been achieved. Nanoparticles containing iron and platinum were also anchored on silaceous supports. The proportion of iron to platinum in FePt nanoparticles was adjusted by altering the molar ratios of starting materials. Consequently, ratios of Fe : Pt of 20 : 80, 27 : 73, 40 : 60, 53 : 47 and 64 : 36 were examined. The materials produced in this manner were characterised by Powder X-ray Diffraction (XRD), BET surface areas and Transmission Electron Microscopy (TEM) and elemental analysis. The FePt materials were also investigated for their magnetic properties by SQUID magnetometry. A number of the metal containing materials were investigated for their potential to produce hydrocarbons in the Fischer–Tropsch synthesis.

Manganese–calcium clusters supported by calixarenes

The structure of the oxygen-evolving complex of photosystem II, which contains a cubane-like metal-oxo cluster incorporating four manganese(III,IV) cations, along with a calcium cation, has focussed attention on synthetic analogues of this cluster. Despite this activity, there are relatively few structurally characterised coordination clusters with this combination of metal cations. The calixarenes are synthetically versatile and well established cluster-supporting ligands, which to date have not been reported to support a calcium/manganese cluster. Here we report that p-t-butylthiacalix[4]arene supports CaMn2 and Ca2Mn2 clusters, whereas reactions of p-t-butylcalix[4]arene, p-t-butylsulfinylcalix[4]arene, and p-t-butylsulfonylcalix[4]arene, under the same conditions, produced only homometallic manganese complexes.

A new selective fluorescent probe based on tamoxifen

Developing targeted validation probes that can interrogate biology is of interest for both chemists and biologists. The synthesis of suitable compounds provides a means for avoiding the costly labeling of cells with specific antibodies and the bias associated with the interpretation of biological validation experiments. The chemotherapeutic agent, tamoxifen has been routinely used in the treatment of breast cancer for decades. Once metabolized, the active form of tamoxifen (4-hydroxytamoxifen) competes with the binding of estrogens to the estrogen receptors (ER). Its selectivity in ER modulation makes it an ideal candidate for the development of materials to be used as chemical probes. Here we report the synthesis of a fluorescent BODIPY®FL conjugate of tamoxifen linked through an ethylene glycol moiety, and present proof-of-principle results in ER positive and ER negative cell lines. Optical microscopy indicates that the fluorescent probe binds selectively to tamoxifen sensitive breast cancer cell lines. The compound showed no affinity for the tamoxifen resistant breast cancer lines. The specificity of the new compound make it a valuable addition to the chemical probe tool kit for estrogen receptors.

Resonance-based detection of magnetic nanoparticles and microbeads using nanopatterned ferromagnets

Biosensing with ferromagnet-based magnetoresistive devices has been dominated by electrical detection of particle-induced changes to a device’s (quasi-)static magnetic configuration. There are however potential advantages to be gained from using field dependent, high frequency resonant magnetization dynamics for magnetic particle detection. Here, we demonstrate the use of nanoconfined ferromagnetic resonances in periodically nanopatterned magnetic films for the detection of adsorbed magnetic particles having diameters ranging from 6 nm to 4???m. The nanopatterned films contain arrays of holes which appear to act as preferential adsorption sites for small particles. Hole-localized particles act in unison to shift the frequencies of the patterned layer’s ferromagnetic-resonance modes, with shift polarities determined by the localization of each mode within the nanopattern’s repeating unit cell. The same polarity shifts are observed for a large range of coverages, even when quasicontinuous particle sheets form above the hole-localized particles. For large particles, preferential adsorption no longer occurs, leading to resonance shifts with polarities that are independent of the mode localization, and amplitudes that are comparable to those seen in continuous layers. Indeed, for nanoparticles adsorbed onto a continuous layer, the particle-induced shift of the layer’s fundamental mode is up to 10 times less than that observed for nanoconfined modes in the nanopatterned systems, the low shift being induced by relatively weak fields emanating beyond the particle in the direction of the static applied field. This result highlights the importance of having particles consistently positioned in the close vicinity of confined modes.

Broad distributions of relaxation times in FePt nanoparticles

Results from magnetic viscosity experiments on chemically synthesized magnetic nanoparticles are presented. Our synthesized Fe20Pt80 particles are distinguished by a narrow size distribution but display features associated with broad distributions of activation rates. Results are presented from viscosity measurements in which the remnant magnetization is measured at different times after the removal of a static field, and studied as a function of temperature. We discuss how these results may be analyzed in terms of activation rate distributions for thermal activated reversal processes after the application and removal of a field. A method for the extraction of energy barrier distributions from directly measured time dependent data is presented.

Magnetic Studies of Metal Ion Coordination Clusters Encapsulated with Thiacalixarene

Three thiacalix[4]arene polynuclear complexes have been prepared by literature methods for detailed magnetic investigation. The [Fe3O(L)2] (LH4 = thiacalix[4]arene) complex is found to exhibit interesting anti-ferromagnetic exchange coupling. Jahn–Teller distortion in [Cu4(L)2] complex leads to strong anti-ferromagnetic coupling at low temperatures. The temperature-dependent susceptibility of the [(μ-H2O)Eu2(LH)2(DMF)4] complex is well described by a ground state involving the thermal population of the lowest three excited states.

Matrix isolation ESR and theoretical studies of metal phosphides

The ZnP, (67)ZnP, CdP, (111)CdP, and (113)CdP radicals have been formed by laser ablation of the metal with GaP pressed into the metal surface, isolated in an inert neon matrix at 4.3 K and their electronic structure was established using electron spin resonance spectroscopy. The following magnetic parameters were determined experimentally for ZnP/(67)ZnP, g(⊥)=1.9982(2), A(⊥)(P)=111(6) MHz, A(⊥)((67)Zn)=160(2) MHz, and D=-29 988(3) MHz and estimates were made for the following ZnP/(67)ZnP magnetic parameters: g(∥)=1.9941(2), A(∥)(P)=-5(6) MHz, and A(∥)((67)Zn)=180(50) MHz. The following magnetic parameters for CdP/(111)CdP/(113)CdP were determined experimentally: g(⊥)=1.9963(2), A(⊥)(P)=97(3) MHz, A(⊥)((111)Cd)=862(3) MHz, and A(⊥)((113)Cd)=902(3) MHz. Evidence for the formation of the MgP radical was also obtained and an approximate hyperfine coupling constant of A(⊥)(P)=157(6) MHz was determined. The low-lying electronic states of ZnP and MgP were also investigated using the multiconfigurational self-consistent field technique. Potential energy surfaces, binding energies, optimized bond lengths, energy separations, and dissociation energies have been determined. Both radicals are found to have (4)Σ(-) ground states with a leading configuration at r(e) of 10σ(2)11σ(2)5π(1)5π(1)12σ(1) for ZnP and 7σ(2)8σ(2)3π(1)3π(1)9σ(1) for MgP. Significant mixing to this state is calculated for MgP.