Coinage metal halide clusters: from two-dimensional ring to three-dimensional solid-state-like structures.
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Biomedical subjects
Anton Hammerl
Publications and source records attributed to Anton Hammerl.
Electrochemically informed synthesis and characterization of salts of the [Pt2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)4]+ lantern complex containing a Pt-Pt bond of order 1/2.
Detailed electrochemical studies in dichloromethane (0.1 M Bu4NPF6) on the oxidation of the half-lantern [Pt2(kappa2As,C-C6H3-5-Me-2-AsPh2)2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)2] (1) and full-lantern [Pt2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)4] (2) complexes reveal the presence of an exceptionally stable dinuclear Pt cation 2+. Thus, oxidation of 1 occurs on the voltammetric time scale via a ladder-square scheme to give 2+, whereas 2 is directly converted to 2+. Electrochemically informed chemical synthesis enabled the isolation of solid [2+][BF4-] to be achieved. Single-crystal X-ray structural analysis showed that 2+ also has a lantern structure but with a shorter separation between the Pt centers [2.7069(3) A (2+), 2.8955(4) A (2)]. EPR spectra of 2+ provide unequivocal evidence for axial symmetry of the complex and are noteworthy because of an exceptionally large, nearly isotropic hyperfine coupling constant of about 0.1 cm(-1). Spectroscopic data support the conclusion that the unpaired electron in the 2+ cation is distributed equally between the two Pt nuclei and imply that oxidation of 2 to 2+ leads to the establishment of the metal-to-metal hemibond. Results of extended Huckel molecular orbital and density functional calculations on 2 and 2+ lead to the conclusions that s, p, dz2 mixing of orbitals contributes to the large EPR Pt hyperfine coupling and also that the structural adjustments that occur upon removal of an electron from 2 are driven by the metal-metal bonding character present in 2+.
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A comparison of structure and stability between the group 11 halide tetramers M4X4 (M = Cu, Ag, or Au; X = F, Cl, Br, or I) and the group 11 chloride and bromide phosphanes (XMPH3)4.
The tetramers of the group 11 (I) halides, M(4)X(4) (M = Cu, Ag, or Au; X = F, Cl, Br, or I), and corresponding group 11 (I) phosphanes, chloride and bromide (XMPH(3))(4) (X = Cl or Br), are investigated by the density functional theory. All coinage metal(I) halide tetramers adopt squarelike ring structures with an out-of-plane distorted (butterfly) D(2d) symmetry. These structures are much lower in energy than the more compact cubelike T(d) arrangements, which maximize dipole-dipole interactions and more closely resemble the solid-state structures of the copper and silver halides. Phosphine coordination completely changes the structures of these M(4)X(4) clusters. The copper(I) and silver(I) phosphane chloride and bromide tetramers adopt a heterocubane structure, slightly preferred over a step (ladder-type)-cluster structure well-known in the coordination chemistry of such compounds. In stark contrast, gold(I) phosphane chloride and bromide tetramers prefer assemblies of linear XAuPH(3) units with direct gold-gold contacts, resulting in a square planar, centered trigonal planar, or tetrahedral gold core.
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F2Al(mu-eta2:eta2-O2)AlF2: an unusual, stable aluminum peroxo compound.
The oxidation processes in the industrial production of aluminum from cryolite melts are not fully understood. Oxidation of AlOF2- leads initially to AlOF2 radicals. The structure of the AlOF2 dimer and several oxidized and reduced forms of this compound are investigated by theoretical methods and compared to analogous boron and gallium compounds. The thermodynamic stability of these compounds is investigated. It is shown that the dimeric compound of AlOF2 contains a symmetric peroxo bridge and is unexpectedly stable toward decomposition.
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Azolylpentazoles as high-energy materials: a computational study.
The structures of highly energetic substituted pentazole compounds and their decomposition to give dinitrogen and the corresponding azide were investigated by ab initio quantum chemical methods. The substituents include azolyl groups (five-membered aromatic rings with different numbers of nitrogen atoms), CH(3), CN, and F. The decomposition pathway was followed for several substituted azolyl- and phenylpentazoles and compared to the known experimental and theoretical results. The NMR parameters of most of the as-yet unknown pentazole compounds were predicted. The activation energy for the decomposition increases, while the decomposition energy of the substituted pentazole decreases with greater electron-donating character of the substituent of the pentazole. Thus, anionic pentazoles are more stable than neutral pentazoles. Methylpentazole is predicted to be among the most stable pentazoles, even though it does not contain an aromatic system.
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Tetrazolylpentazoles: nitrogen-rich compounds.
Tetrazolylpentazole was identified as an intermediate in the reaction of tetrazolediazonium chloride with lithium azide by low-temperature (15)N NMR spectroscopy. The decomposition of (15)N-labeled tetrazolylpentazole to form (15)N-labeled tetrazoleazides and dinitrogen was followed by low-temperature (15)N NMR spectroscopy. The structures of the species involved in this decomposition were optimized at different levels of theory, and the structures of the transition states were identified. The activation barriers for the decomposition were calculated at different levels of theory.
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