Showing papers by "Bernt Krebs published in 2008"
TL;DR: In this article, a dinuclear zinc compound [Zn2(L1)2]·N(CH2CH3)3 (1) was synthesized, which is considered to be structural model for the active sites in phospholipase C and nuclease P1.
Abstract: Starting from the tripodal tetradentate ligands -(3,5-dibromo-2-hydroxybenzyl)(2-hydroxybenzyl)(2-pyridyl)methylamine (H2L1), (3,5-dibromo-2-hydroxybenzyl)(2-hydroxy-5-nitrobenzyl)(2-pyridyl)methylamine (H2L2), and (3,5-dichloro2-hydroxybenzyl)(2-hydroxy-5-nitrobenzyl)(2-pyridyl)methylamine (H2L3) the new isostructural dinuclear zinc compounds [Zn2(L1)2]·N(CH2CH3)3 (1), [Zn2(L2)2]·2CH3OH (2) and [Zn2(L3)2]·C4H10O (3) were synthesized. Due to their enzyme-like trigonal bipyramidal N2O3 coordination environment of the zinc ions and the similar Zn···Zn distances the complexes can be considered to be structural models for the active sites in phospholipase C and nuclease P1. With H2L3 also the dinuclear complex [Co2(L2)2(CH3OH)]·2CH3OH·0.5C4H10O (4) could be prepared.
The new compounds were isolated and characterized by single crystal X-ray crystallography as well as infrared spectroscopy. The cobalt compound 4 was additionally characterized by UV-Vis spectroscopy and magnetic measurements. 1 crystallizes in the monoclinic space group P21/n with a = 11.2814(2), b = 28.6154(2), c = 13.1866(3) A, β = 96.995(1)°, V = 4225.2(2) A3, Z = 4. 2 and 3 are monoclinic, space group C2/c with a = 23.084(5), b = 9.232(2), c = 21.849(4) A, &β; = 96.83(3)°, V = 4623(2) A3, Z = 4, and a = 22.7834(3), b = 9.2463(1), c = 21.6351(3) A, &β; = 97.592(1)°, V = 4517.7(2) A3, Z = 4, respectively. 4 crystallizes in the monoclinic space group I2/a with a = 22.4680(4), b = 20.5517(4), c = 22.8910(6) A, &β; = 111.938(1)°, V = 9804.7(4) A3, Z = 8. 4 shows an effective magnetic moment of 6.72 μB at 300 K which clearly indicates the presence of two cobalt(II) high spin ions with Curie-Weiss behaviour above 80 K. At lower temperatures a decrease of the effective magnetic moment was observed.
12 citations
TL;DR: In this paper, two crown ether-assisted oxonium bromoselenates (II,IV) and two crown-assisted halogenochalcogenates (III and IV) are reported.
Abstract: Novel Oxonium Halogenochalcogenates Stabilized by Crown Ethers: [H3O(Dibromo-benzo-18-crown-6)]2[Se3Br10] and [H5O2(Bis-dibromo-dibenzo-24-crown-8]2[Se3Br8]
Two novel complex oxonium bromoselenates(II,IV) and –(II) are reported containing [H3O]+ and [H5O2]+ cations coordinated by crown ether ligands. [H3O(dibromo-benzo-18-crown-6)]2[Se3Br10] (1) and [H5O2(bis-dibromo-dibenzo-24-crown-8]2[Se3Br8] (2) were prepared as dark red crystals from dichloromethane or acetonitrile solutions of selenium tetrabromide, the corresponding unsubstituted crown ethers, and aqueous hydrogen bromide. The products were characterized by their crystal structures and by vibrational spectra. 1 is triclinic, space group (Nr. 2) with a = 8.609(2) A, b = 13.391(3) A, c = 13.928(3) A, α = 64.60(2)°, β = 76.18(2)°, γ = 87.78(2)°, V = 1404.7(5) A3, Z = 1. 2 is also triclinic, space group with a = 10.499(2) A, b = 13.033(3) A, c = 14.756(3) A, α = 113.77(3)°, β = 98.17(3)°, γ = 93.55(3)°. V = 1813.2(7) A3, Z = 1. In the reaction mixture complex redox reactions take place, resulting in (partial) reduction of selenium and bromination of the crown ether molecules. In 1 the centrosymmetric trinuclear [Se3Br10]2− consists of a central SeIVBr6 octahedron sharing trans edges with two square planar SeIIBr4 groups. The novel [Se3Br8]2− in 2 is composed of three planar trans-edge sharing SeIIBr4 squares in a linear arrangement. The internal structure of the oxonium-crown ether complexes is largely determined by the steric restrictions imposed by the aromatic rings in the crown ether molecules, as compared to complexes with more flexible unsubstituted crown ether ligands.
3 citations