Gary D. Enright

Single-Molecule Magnet Behavior for an Antiferromagnetically Superexchange-Coupled Dinuclear Dysprosium(III) Complex

A family of five dinuclear lanthanide complexes has been synthesized with general formula [Ln(III)(2)(valdien)(2)(NO(3))(2)] where (H(2)valdien = N1,N3-bis(3-methoxysalicylidene)diethylenetriamine) and Ln(III) = Eu(III)1, Gd(III)2, Tb(III)3, Dy(III)4, and Ho(III)5. The magnetic investigations reveal that 4 exhibits single-molecule magnet (SMM) behavior with an anisotropic barrier U(eff) = 76 K. The step-like features in the hysteresis loops observed for 4 reveal an antiferromagnetic exchange coupling between the two dysprosium ions. Ab initio calculations confirm the weak antiferromagnetic interaction with an exchange constant J(Dy-Dy) = -0.21 cm(-1). The observed steps in the hysteresis loops correspond to a weakly coupled system similar to exchange-biased SMMs. The Dy(2) complex is an ideal candidate for the elucidation of slow relaxation of the magnetization mechanism seen in lanthanide systems.

Population inversion in the recombination of optically-ionized plasmas

The possibility of using a high-intensity optical field in conjunction with a gas target to produce a highly ionized plasma filament suitable for recombination XUV lasers in both transient and quasi-steady-state regimes is examined. A distinction is made between low Z ions which can be stripped to the desired ionization state at nonrelativistic intensities and higher Z ions which require relativistic intensities to produce the desired ionization. In the nonrelativistic case (E/sub i/ >

ISOMERISM AND BLUE ELECTROLUMINESCENCE OF A NOVEL ORGANOBORON COMPOUND : BIII2(O)(7-AZAIN)2PH2

Bright blue light with a maximum at 450 nm is emitted by both structural isomers of the novel, stable BIII2 (O)(7-azain)2 Ph2 (7-azain=7-azaindole anion) on irradiation with UV light. The isomer shown in the picture has approximate C2 symmetry (the other isomer approximate Cs symmetry) and electroluminesces when used as the emitting layer in an electroluminescent device.

Structure H Hydrate: A Single Crystal Diffraction Study of 2,2-dimethylpentane·5(Xe, H2S)·34H2O

Abstract Although Structure H hydrate has been studied intensively for a number of years, its detailed crystal structure has remained unknown. Single crystal X-ray diffraction was used to determine the structure of 2,2-dimethylpentane·5(Xe, H2S)·34H2O hydrate. The hexagonal unit cell, space group P6/mmm with z=1, has the following parameters: a = 12.212(2), c = 10.143(2) A (t = −100°C). Cage geometries and fractional coordinates for the atoms are presented and discussed. Structure H hydrate is only the third hydrate type for which a large number of molecules are suitable as guests.

The ferrocene moiety as a structural probe: redox and structural properties of ferrocenoyl-oligoprolines FcPronOBzl (n=1–4) and FcPro2PheOBzl

Abstract The preparations of the five ferrocenoyl-oligopeptides, FcProOBzl (1), FcPro2OBzl (2), FcPro3OBzl (3), FcPro4OBzl (4) and FcPro2PheOBzl (5) are described. Crystallographic studies show that the Fc-oligoprolines 1–4 adopt a helical polyproline II structure having all prolines in a mutually trans-conformation. This structure is maintained in MeCN and CHCl3 solutions, as was shown by NMR methods. Chemical and magnetic similarities among the proline residues render spectral assignment by conventional 1D 1H-NMR spectroscopy impossible. However, a combination of 2D NMR techniques allowed us to unequivocally assign all signals. The redox potential of the Fc-group attached to the oligoproline chain is sensitive to the sequence and length of the oligopeptide. With growing peptide length, the molecule becomes easier to oxidize.

Self‐Assembly of Lamellar and Expanded Lamellar Coordination Networks

Structural similarity with clay-type minerals is apparent in the self-assembled layered coordination network [{Ag(1)(MeCN)2 }∞ ][BF4 ]∞ , which is stabilized by a lamellar chelate effect (section of structure shown on the right). The interlayer region is expandable through the use of larger ligands such as PhCN. The void space is occupied by one PhCN molecule per repeat unit.

Coordination polymers of cobalt(II): [Co(4,4′-bpy)2(O2CCF3)2]n and [Co(4,4′-bpy)(O2CCH3)2(H2O)2]n

Two novel coordination polymers of cobalt(II) have been synthesized and characterized structurally. The first compound, [Co(4,4′-bpy)2(O2CCF3)2] (1), was obtained from the reaction of Co(O2CCF3)2 with 4,4′-bipyridine. Compound 1 has a covalently linked, two-dimensional, fishing-net-like structure. The fishing nets of 1 stack in the lattice, allowing the formation of extended channels that host diethyl ether solvent molecules in the solid state. The second compound, [Co(4,4′-bpy)(O2CCH3)2(H2O)2] (2), was obtained from the reaction of Co(CH3CO2)2·4H2O with 4,4′-bipyridine. Compound 2 has a covalently linked one-dimensional chain structure. In the crystal lattice of 2 the one-dimensional chains form an interpenetrating, three-dimensional structure via interchain hydrogen bonds between acetate and H2O ligands. There are channels parallel to the b axis in the lattice of 2 that appear to host small guest molecules such as methanol and H2O.

t-Butylcalix[4]arene compounds with long chain guests ☆: structures and host–guest interactions

Abstract This crystal structure study examines systematically the effect of guest size and guest substituents on the guest–host interactions in a number of simple p-tert-butylcalix[4]arene host–guest compounds. With increasing chain length, the guest conformation becomes increasingly complex, going from a simple all-trans (C6) to s-shaped (C8) and helical (C12) conformations. For Cl-substituted alkanes, the Cl atom is excluded from the deep cavity, again by the chain taking on complex conformations. However, the Cl atom can be forced into the deep cavity with rigid guests such as 1,4-dichlorobenzene. The results suggest that it is space filling rather than specific interactions that give these compounds stability, and that they should be properly described as clathrates rather than as stoichiometric host–guest materials.

Modified Metal Dibenzoylmethanates and their Clathrates. Part I. Clathration Ability of dipyridinebis(dibenzoylmethanato)nickel(II), a Novel Metal-Complex Host [1]

Abstract The title complex, [NiPy2(DBM)2] (DBM = C6H5CO CHCOC6H5, dibenzoylmethanate), entraps solvent molecules upon crystallization. Six clathrates of four structural types have been studied by single-crystal X-ray diffraction (guest, host:guest molar ratio, crystal system, space group, formula units per unit cell): (I) carbon tetrachloride, 1:2, orthorhombic, P212121, Z = 4; (II) pyridine, 1:2, monoclinic, C2/c, Z = 8; (III) benzene, 1:1, monoclinic, C2/c, Z = 8; (IV) chlorobenzene, 1:1, monoclinic, C2/c, Z = 8; (V) chloroform, 1:2, monoclinic, P21/n, Z = 2; (VI) tetra-hydrofuran, 1:2, monoclinic, P21/n, Z = 2. A non-clathrate form of the complex (VII) was obtained from acetone; it is triclinic, P1, Z = 1. The compounds I-VII are consistent with van der Waals type of packing. The complex unit is formed by octahedral coordination to nickel of four oxygen and two nitrogen atoms from two chelate DBM and two pyridine molecules, respectively. In all seven compounds the host complex is trans-configured. Comp...

Gradual spin crossover behaviour in a linear trinuclear FeII complex

The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex, [FeII3(npt)6(EtOH)4(H2O)2](ptol)6·4EtOH (1), and of its CoII (2 and 3) and NiII (4) analogues, are reported here. The complexes were synthesized by reacting a 1,2,4-triazole-based ligand, 4-(4′-nitrophenyl)-1,2,4-triazole (npt), with the p-tolylsulfonate (ptol) metal salts in methanol or ethanol. Structural analyses revealed that all complexes are iomorphous and consist of a linear trinuclear core where metal centres are bridged by triazole groups. For 1, dc susceptibility measurements exhibit gradual spin transition with T1/2 = 148 K which corresponds to HS → LS crossover for the triazole bridged central FeII ion. This spin transition was confirmed by Single-Crystal X-Ray Diffraction data of 1 at 100 K and 181 K, where the low temperature measurement revealed a decrease in volume for the central FeII ion, which is in agreement with a HS → LS transition.