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We report here the synthesis and the investigation of the magnetic properties of a series of binu... more We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga 4 Ln 2 (shi 3À ) 4 (Hshi 2À ) 2 (H 2 shi À ) 2 (C 5 H 5 N) 4 (CH 3 OH) x (H 2 O) x ]$ xC 5 H 5 N$xCH 3 OH$xH 2 O (where H 3 shi ¼ salicylhydroxamic acid and Ln ¼ Gd III 1; Tb III 2; Dy III 3; Er III 4; Y III 5; Y III 0.9 Dy III 0.1 6). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field.

Tuning the Ising-type anisotropy in trigonal bipyramidal Co(II) complexes We can tune the Ising-t... more Tuning the Ising-type anisotropy in trigonal bipyramidal Co(II) complexes We can tune the Ising-type anisotropy in trigonal bipyramidal Co(II) complexes using simple ligand theory considerations. We used a sulfur containing ligand to synthesize a complex that had long equatorial Co–S bonds. This complex exhibits a larger anisotropy barrier and a longer relaxation time in comparison to the complex prepared with a nitrogen-containing ligand.

A dysprosium(III) complex, exhibiting slow relaxation of magnetization, was prepared. Crystallogr... more A dysprosium(III) complex, exhibiting slow relaxation of magnetization, was prepared. Crystallographic studies showed a perturbation of local symmetry upon deprotonation of the ligand, with concomitant faster relaxation of magnetization. This was attributed to a large shift in the direction of the main magnetic axis, as indicated by ab initio calculations. † Electronic supplementary information (ESI) available: Full experimental details including additional crystallographic, spectroscopic magnetic and theoretical data. CCDC 870723 and 870724. For ESI and crystallographic data in CIF or other electronic format see

Inorganic Chemistry, 2014

We investigate and compare the magnetic properties of two isostructural Dy III -containing comple... more We investigate and compare the magnetic properties of two isostructural Dy III -containing complexes. The Dy III ions are chelated by hexadentate ligands and possess two apical bidendate nitrate anions. In dysprosium(III) N,N′bis(imine-2-yl)methylene-1,8-diamino-3,6-dioxaoctane (1), the ligand's donor atoms are two alkoxo, two pyridine, and two imine nitrogen atoms. Dysprosium(III) N,N′-bis(amine-2yl)methylene-1,8-diamino-3,6-dioxaoctane (2) is identical with 1 except for one modification: the two imine groups have been replaced by amine groups. This change has a minute effect on the structure and a larger effect the magnetic behavior. The two complexes possess slow relaxation of the magnetization in the presence of an applied field of 1000 Oe but with a larger barrier for reorientation of the magnetization for 1 (U eff /k B = 50 K) than for 2 (U eff /k B = 34 K). First-principles calculations using the spin−orbit complete active-space self-consistent-field method were performed and allowed to fit the experimental magnetization data. The calculations gave the energy spectrum of the 2J + 1 sublevels issued from the J = 15 / 2 free-ion ground state. The lowest-lying sublevels were found to have a large contribution of M J = ± 15 / 2 for 1, while for 2, M J = ± 13 / 2 was dominant. The observed differences were attributed to a synergistic effect between the electron density of the ligand and the small structural changes provoked by a slight alteration of the coordination environment. It was observed that the stronger ligand field (imine) resulted in complex 1 with a larger energy barrier for reorientation of the magnetization than 2.

Inorganic Chemistry, 2013

A family of lanthanide complexes has been synthesized by the subcomponent self-assembly methodolo... more A family of lanthanide complexes has been synthesized by the subcomponent self-assembly methodology. Molecular architectures, which were stable in solution and under ambient conditions, were designed by the in situ formation of ligands around lanthanide ion templates. Magnetic studies indicated that, despite the low C 2 symmetry, 1 and 2 display single molecule magnet (SMM) behavior, with 1 exhibiting an effective energy barrier of the relaxation of the magnetization U eff /k B = 50 K and the pre-exponential factor τ o = 6.80 × 10 −7 s.

Nature Chemistry, 2010

Molecular subcomponents such as phosphate groups are often passed between biomolecules during com... more Molecular subcomponents such as phosphate groups are often passed between biomolecules during complex signalling cascades, the flow of which define the motion of the machinery of life. Here, we show how an abiological system consisting of organic subcomponents knitted together by metal-ion coordination can respond to simple signals in complex ways. A Cu I 3 helicate transformed into its Zn II 2 Cu I analogue following the addition of zinc(II), and the ejected copper(I) went on to induce the self-assembly of a Cu I 2 helicate from other free subcomponents present in solution. The addition of an additional subcomponent, 8-aminoquinoline, resulted in the formation of a third, more stable Cu I 3 helicate, requiring the destruction of both the Zn II 2 Cu I and Cu I 2 helicates to scavenge sufficient Cu I for the new structure. This system thus demonstrates two examples in which the application of one signal provokes two distinct responses involving the creation or destruction of complex assemblies as the system seeks thermodynamic equilibrium following perturbation.

Chemistry A European Journal, 2009

Chemistry A European Journal, 2008

Physical Review Letters, 2007

Journal of Polymer Science: Part A: Polymer Chemistry, 2007

A family of fluorinated azobenzene-based push-pull chromophores with one, two, and three trifluor... more A family of fluorinated azobenzene-based push-pull chromophores with one, two, and three trifluorovinyl ether (TFV) groups in linear and branched architecture was synthesized and utilized as active materials in the low optical loss electrooptic (EO) composites. The fluorinated azobenzene chromophores exhibited increased solubility (30-50 wt %) in semifluorinated polymer host, such as perfluorocyclobutane (PFCB) aromatic ether resin after crosslinking, compared with the commercially available nonfluorinated azobenzene chromophore Disperse Red 1 (1-2 wt %). The impact of this approach on the optical properties on the polymer blends is assessed through optical propagation loss measurements and EO characterization. The resulting fluorinated EO composites showed excellent optical clarity, low birefringence, and low optical loss less than 0.5 dB/cm, while giving EO coefficients of about 3-7 pm/V at 1550 nm. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3166-3177, 2007 Scheme 1. Synthesis of chromophore A and B. 3168 CAMPBELL ET AL.

$Research paper thumbnail of Chromophore Orientation Dynamics, Phase Stability, and Photorefractive Effects in Branched Azobenzene Chromophores$

Macromolecules, 2006

The increased solubility and uniform dispersal of branched azobenzene chromophores over their mon... more The increased solubility and uniform dispersal of branched azobenzene chromophores over their monomeric analogues have been shown to improve the electrooptic performance of high glass transition temperature (T g ) blended polymers. We report here the application of these branched chromophores as guest nonlinear optical molecules in the plasticized low-T g photoconducting host polymer poly(vinylcarbazole) and demonstrate the presence of orientationally enhanced photorefractive index gratings. When compared with their monomeric analogues, branched chromophores were compatible over a broader range of concentrations and resulted in higher quality optical films; these films have retained their optical clarity for 1 year. A new branched electrooptic chromophore with r 33 of 14 pm/V at 1550 nm was synthesized and exhibited photorefractive two-beam coupling over a range of applied fields, including a net two-beam coupling amplification coefficient of 6.4 cm -1 at 780 nm.

Chemistry of Materials, 2005

We describe the integration of a photochromic azobenzene dye into electrostatically bound polyele... more We describe the integration of a photochromic azobenzene dye into electrostatically bound polyelectrolyte multilayers. Two different deposition techniques are compared: electrostatic self-assembly (ESA) and polyelectrolyte spin-assembly. The polyelectrolytes used were PEI (polyethylenimine) and PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]). Successful incorporation of the azobenzene dye Direct red 80 (DR80) into ESA and spin-assembled multilayered films (PEI/DR80) is demonstrated. We find that coadsorption of DR80 and PAZO on a PEI surface occur in different proportions and packing densities, depending on the assembly technique selected. We find that using DR80 as a coadsorbing agent can dramatically enhance the rate of PAZO adsorption, and we observe different deposition rates for DR80 and PAZO when the two materials adsorb simultaneously from a common solution.