Application of quantum-chemical methods including density functional theory for the interpretation of isotropic hyperfine data. The example of azulenebenzoquinone

The radical anion of aceneazulenedione in which a benzoquinone is fused to an azulene moiety was generated by electrolysis and by reduction with the alkali metals in ethereal solvents. The hyperfine data could not be reproduced by standard Hückel calculations which usually give reliable predictions for the spin distribution in radical ions such as azulene quinones and a variety of extended π systems. However, PPP and, preferably,ab initio geometry optimisations followed by single-point calculations of the Fermi contact interaction with density functional theory, led to a straightforward assignment of the hyperfine coupling constants.     

Chemie der lithium-enolat-heptafulvene: regiospezifische aldol-addition

Aldehydes and ketones add to the cycloheptatriene ester anion $\text{2a}$ and to the carboxylic acid dianion $\text{2b}$ at C-7 (α-attack) or C-2 (C-5) (γ-attack), depending on the starting compounds.     

Metal- and ligand-directed one-pot syntheses,crystal structures,and properties of novel oxo-centered tetra- and hexametallic clusters

Starting from closely related metal-ligand combinations, completely different oligomeric metal clusters are synthesized. Whereas, picoline-tetrazolylamide HL(1) (1) and zinc or nickel acetate afforded [2x2] grids [M(4)(L(1))(8)] (2), slightly different N-(2-methylthiazole-5-yl)-thiazole-2-carboxamide HL(2) (5 a) and nickel acetate yielded the monometallic complex [Ni(L(2))(2)(OH(2))(2)] (6). In contrast, reaction of 5 a with zinc acetate produced the tetrametallic zinc cluster [Zn(4)O(L(2))(4)(OAc)(2)] (7). Even more surprising, when 3-methyl-substituted HL(3) (5 b) instead of 2-methyl-substituted HL(2) (5 a) was allowed to react under identical conditions with zinc acetate, the cluster [Zn(4)O(L(3))(4)Cl(2)] (8) crystallized from dichloromethane. Clusters 7 and 8 are isostructural. As for 7, in 8 two of the edges of the tetrahedron of zinc ions are doubly bridged, two are singly bridged, and the other two are nonbridged. On the other hand, when iron(II) acetate under aerobic conditions was allowed to react with 5 a, the unprecedented complex [[Fe(3)O(L(2))(2)(OAc)(4)](2)O] (9) was isolated. Cluster 9 is composed of two trimetallic, triangular mu(3)-O(2-)-centered [Fe(3)O(L(2))(2)(OAc)(4)](+) modules, linked by an almost linear mu(2)-O(2-) bridge. The M?ssbauer spectrum together with cyclic voltammetric and square-wave voltammetric measurements of 9 are reported, and 6-9 were characterized unequivocally by single-crystal X-ray structure analyses.     

Optically active cyclic hexapeptides with covalently attached pyrene probes: selective alkaline earth metal ion recognition using excimer emission

[structure: see text] The synthesis of two optically active pyrene-modified cyclic hexapetides and their selectivity toward the complexation of alkaline earth metal ions are reported. Complexation was studied by optical and chiroptical methods. The cyclic peptides are forming 2:1 sandwich complexes with the metal ions.     

Redox-switchable squaraines with extended conjugation

[reaction: see text] The redox chemistry of pi-extended squaraines is investigated using cyclic voltammetry, in-situ spectroelectrochemistry and quantum chemical calculations. Squaraine 1 is reversibly oxidized to the radical cation and dication whereas reduction shows limited electrochemical but fully chemical reversibility. The radical cation of 1 reveals absorption bands at 1000 nm and a "two-band feature" at 1600 nm. Their implications on the intramolecular electron transfer are discussed.     

Synthesis,Crystal Structure and Vibrational Spectra of Barium Cyclotetraphosphate Hydrate Ba2(P4O12)∙3.5H2O

Barium tetrametaphosphate hydrate Ba₂(P₄O₁₂)∙3.5H₂O was synthesized as a single‐phase crystalline powder starting from an aqueous solution of barium hydroxide and phosphorus pentoxide at 300 K. Ba₂(P₄O₁₂)∙3.5H₂O crystallizes in a new structure type in which the Ba²⁺ ions form a distorted hexagonal diamond‐like arrangement with the (P₄O₁₂)^4– anions in the trigonal prismatic voids (Ba₂(P₄O₁₂)∙3.5H₂O, C2/c, Z = 4, a = 777.3(2), b = 1297.6(2), c = 1346.1(3) pm, b = 95.38(2)°, wR₂ = 0.071, R₁ = 0.018, 1180 reflections, 118 parameters). The vibrational spectra of Ba₂(P₄O₁₂)∙3.5H₂O and its thermal behavior up to 720 K are also reported.