Robert W. Gable

A new type of interpenetration involving enmeshed independent square grid sheets. The structure of diaquabis-(4,4′-bipyridine)zinc hexafluorosilicate

Zn(4,4′-bipy)2SiF6·2H2O (4,4′-bipy = 4,4′-bipyridine) consists of two perpendicular and equivalent stacks of infinite, essentially square grid [Zn(H2O)2(4,4′-bipy)2]n2n+ sheets, which interpenetrate so that any particular sheet has an infinite number of perpendicular ones enmeshed or concatenated with it.

Utilizing the Adaptive Polyoxometalate [As2W19O67(H2O)]14– To Support a Polynuclear Lanthanoid-Based Single-Molecule Magnet

Five members of a new family of polyoxometalate (POM)-ligated tetranuclear rare earth metal complexes have been synthesized and characterized. These compounds have the general formula (HDABCO)(8)H(5)Li(8)[Ln(4)As(5)W(40)O(144)(H(2)O)(10)(gly)(2)]·25H(2)O [Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Y = (5), HDABCO = monoprotonated 1,4-diazabicyclooctane, gly = glycine] and were synthesized from the preformed POM precursor [As(2)W(19)O(67)(H(2)O)](14-). The structure is comprised of two {As(2)W(19)O(68)} building blocks linked by a unit containing four rare earth ions and two additional tungsten centers, with the two glycine ligands playing a key bridging role. Two crystallographically distinct rare earth ions are present in each complex, both of which possess axially compressed, approximate square antiprismatic coordination geometry. The variable-temperature magnetic susceptibility profiles for 2-4 are dominated by population/depopulation of the M(J) sublevels of the relevant ground terms, and fitting of the data has afforded the ligand field parameters in each case, from which the energies of the M(J) sublevels can be calculated. Alternating current magnetic susceptibility data have revealed the onset of slow magnetic relaxation for 3, with the energy barrier to magnetization reversal determined to be 3.9(1) K. As for other lanthanoid complexes that display slow magnetic relaxation, this energy barrier is due to the splitting of the M(J) sublevels of the Dy(3+) ions such that the ground sublevel has a relatively large |M(J)| value, thereby affording Ising-type magnetic anisotropy. This complex is thus the first POM-supported polynuclear lanthanoid-based SMM. Simulation of the W-band EPR spectrum of 1 has afforded the spin Hamiltonian parameters for this species, while the X-band EPR spectrum of 3 indicates the presence of a non-negligible fourth-order transverse component of the anisotropy, which is responsible for the small effective energy barrier observed for 3 and the absence of slow magnetic relaxation for 4.

Design and synthesis of type-III mimetics of ω-conotoxin GVIA

Our interest lies in the rational design and synthesis of type-III mimetics of protein and polypeptide structure and function. Our approach involves interactive design of conformationally defined molecular scaffolds that project certain functional groups in a way that mimics the projection of important binding residues as determined in the parent structure. These design principles are discussed and applied to the structurally defined polypeptide, ω-conotoxin GVIA, which blocks voltage-gated, neuronal N-type calcium channels. These ion channels represent therapeutic targets for the development of new analgesics that can treat chronic pain. It is shown how a discontinuous, 3-residue pharmacophore of GVIA can be mimicked by different molecular scaffolds. It is illustrated how such 1st generation leads must necessarily be weak and that optimisability must therefore be built-in during the design process.

Reversible and non-reversible inclusion compounds of the nickel xanthate adducts with 4,4'-bipyridyl and with 2,2'-dipyridylamine

Abstract The crystal structures of the benzene inclusion compound of the 2,2′dipyridylamine nickel ethylxanthate adduct, [Ni(S2COEt)2(2,2′-dpa)·C6H6], and the carbon tetrachloride inclusion compound of the 4,4′-bipyridyl nickel butylxanthate adduct, [Ni(S2COBu)2(4,4′-bipy)·2CCl4]n, have been determined by single crystal X-ray diffraction methods. Crystals of [Ni(S2COEt)2(2,2′-dpa)·C6H6] are triclinic, space group P 1 , a = 8.755(2), b = 12.680(3), c = 13.012(3) A, and α = 110.12(2), β = 106.09(2), γ = 92.56(2)° with Z = 2; R and Rw were 0.060 and 0.064 respectively for 3073 unique observed reflections. The nickel atom is in an octahedral environment, surrounded by two chelating xanthate ligands and one chelating 2,2′-dpa molecule. The benzene molecules sit in cavities formed by the packing of the [Ni(S2-COEt)2(2,2′-dpa)] molecules, there being two benzene molecules in each cavity. Crystals of [Ni(S2COBu)2(4,4′-bipy)·2CCl4]n are triclinic, space group P 1 , a = 6.6349(8), b = 11.3135(9), c = 13.1101(9) A, α 64.454(7), β = 79.551(8), γ = 84.984(8)°, Z = 2; R and Rw were 0.040 and 0.044 respectively for 3018 unique reflections. The nickel atom is in an octahedral environment which results from two chelating xanthate ligands and two nitrogen atoms, one from each of two, 4,4′-bipyridyl ligands. The nitrogen atoms are in a trans configuration which gives rise to a linear polymer of composition [Ni(S2COBu)2(4,4-bipy)]n. The CCl4 molecules sit in open channels, parallel to the a-axis, which are formed by the packing of the linear polymeric chains of the complex.

Crystal structures of Ph2Te(S2P(OEt)2)2 and of two modifications of Ph2Te(S2CNEt2)2

Abstract Crystals of Ph 2 Te[S 2 CNEt 2 ] 2 are monclinic; one modification has space group P 2 1 , a 8.3349(9), b 8.389(1), c 18.106(2) A, β 92.51(1)°, Z = 2. The second modification of Ph 2 Te[S 2 CNEt 2 ] 2 has space group C 2/ c , a 16.552(2), b 14.363(3), c 12.184(2) A, β 121.61(1)°, Z = 4. Crystals of Ph 2 Te[S 2 (OEt) 2 ] 2 ( 3 ) are orthorhombic, space group P 2 1 2 1 2 1 , a 8.297(1), b 16.311(3), c 21.117(3) A. All three structures are monomeric and contain a stereochemically active lone pair at the tellurium atom, making the Te effectively seven coordinate in each case.

Characterization of the Two Fundamental Conformations of Benzoylureas and Elucidation of the Factors That Facilitate Their Conformational Interchange

The ability of the benzoylurea core to mimic alpha helices relies on its ability to form an intramolecular hydrogen bond. The conformational behavior of benzoylureas is investigated in depth in this study via the use of NMR, IR, X-ray, and computational analysis. The results show that the closed conformation maintained by an intramolecular hydrogen bond is favored in most of the cases studied except when steric and electronic effects combined with a solvent possessing a high hydrogen bond accepting ability, such as DMSO, are involved. The study highlights the propensity for benzoylureas to switch conformation depending on the environment of the molecule for a particular set of substituents. We anticipate that our summary of the phenomenon of internal hydrogen bonding and its analysis may further serve as a useful reference source for future workers in this area.

Synthesis and Biological Evaluation of Chalcones as Inhibitors of the Voltage-Gated Potassium Channel Kv1.3

Chalcone derivatives of the natural product khellinone were synthesised and screened for bioactivity against the voltage-gated potassium channel Kv1.3. X-ray crystallography was employed to investigate relationships between the structure and function of a selection of the reported chalcones.

Investigation of organoyltellurium(IV) halide (dithiolate) complex, crystal structure of di(2-iodo-2λ4-benzotellurol-2-yl diethyldithiocarbamate), [C8H8Te(I)(S2CNEt2)]2

Abstract 125Te NMR data indicate the formation of mixed-ligand species C8H8Te(X)(SS) (X = Cl, Br, I; SS = S2CNEt2, S2P(OR)2, S2COR) in mixtures of C8H8TeX2 and C8H8Te(SS)2. These ligand redistribution reactions are solvent dependent for SS = S2P(OR)2, S2COR. No evidence was found for the existence of the mixed-ligand species C8H8Te(F)(SS). Crystals of [C8H8Te(I)(S2CNEt2)]2 are orthorhombic, space group Pccn with Z = 8, a 13.061(2), b 19.130(2), c 14.043(2). The compound is dimeric through asymmetric iodine bridges; there is evidence of a stereochemically active lone pair which gives an overall seven coordinate 1:2:2:2 geometry about the tellurium atom.

Haloxanthates of antimony(III) and bismuth(III): Crystal structure of Sb(S2COEt)2Br

Abstract The complexes Sb(S2COEt)2X (X = Cl, Br, I) and Bi(S2COEt)2X (X = Cl, Br) have been isolated as cystalline compounds. From infrared spectra and molecular weight determinations it is concluded that they are polymeric in the solid state but dissociate in solution. An X-ray structure determination of Sb(S2COEt)2Br shows that the antimony atom is six coordinate, with the bromine atoms forming bridges between pairs of antimony atoms leading to a zigzag chain. The unit cell is monoclinic, space group P21/c, with a = 10.769(2), b = 16.462(2), c = 8.360(2) A, and β = 110.71(2)°.

Modular Molecules: Site‐Selective Metal Substitution, Photoreduction, and Chirality in Polyoxometalate Hybrids

The first members of a promising new family of hybrid amino acid-polyoxometalates have emerged from a search for modular functional molecules. Incorporation of glycine (Gly) or norleucine (Nle) ligands into an yttrium-tungstoarsenate structural backbone, followed by crystallization with p-methylbenzylammonium (p-MeBzNH3(+)) cations, affords (p-MeBzNH3)6K2(GlyH)[As(III)4(Y(III)W(VI)3)W(VI)44Y(III)4O159(Gly)8(H2O)14]⋅47 H2O (1) and enantiomorphs (p-MeBzNH3)15(NleH)3[As(III)4(Mo(V)2Mo(VI)2)W(VI)44Y(III)4O160(Nle)9(H2O)11][As(III)4(Mo(VI)2W(VI)2)W(VI)44Y(III)4O160(Nle)9(H2O)11] (generically designated 2: L-Nle, 2 a; D-Nle, 2 b). An intensive structural, spectroscopic, electrochemical, magnetochemical and theoretical investigation has allowed the elucidation of site-selective metal substitution and photoreduction of the tetranuclear core of the hybrid polyanions. In the solid state, markedly different crystal packing is evident for the compounds, which indicates the role of noncovalent interactions involving the amino acid ligands. In solution, mass spectrometric and small-angle X-ray scattering studies confirm maintenance of the structure of the polyanions of 2, while circular dichroism demonstrates that the chirality is also maintained. The combination of all of these features in a single modular family emphasizes the potential of such hybrid polyoxometalates to provide nanoscale molecular materials with tunable properties.