Als Urmaass bei der Acidimetrie und Alkalimetrie

Ohne Zusammenfassung     

Characterization of Mixed Crystals in the System Cu2MnxCo1−xGeS4 and Investigations of the Tetrahedra Volumes

In a series of investigations on normal tetrahedral compounds we present mixed crystals in the system Cu₂Mn_xCo_1?xGeS₄ (0 < x < 1) and an inspection of their tetrahedra volumes. Cu₂CoGeS₄ crystallizes tetragonal in a stannite type structure, Cu₂MnGeS₄ crystallizes orthorhombic in the wurtzstannite structure type. The crystal structures of Cu₂CoGeS₄ and Cu₂Mn_0.68Co_0.32GeS₄ were refined from single crystal diffraction data. The refinement of Cu₂CoGeS₄ converged to R = 0.0547 and wR2 = 0.0847 for 299 unique reflections. The refinement of Cu₂Mn_0.68Co_0.32GeS₄ converged to R = 0.0481 and wR2 = 0.0877 for 1556 unique reflections. From these data the tetrahedra volumes of the end members and of Cu₂Mn_0.68Co_0.32GeS₄ are calculated. In Cu₂CoGeS₄ tetrahedra [MS₄] are similar in size. In contrast, the differences of the volumes of the polyhedra [MS₄] in the orthorhombic wurtzite superstructure type compounds Cu₂MnGeS₄ and Cu₂Mn_0.68Co_0.32GeS₄ are significant (M = Cu, Mn, (Mn_0.68Co_0.32), Co, Ge). From x = 0 to x = 0.5 the tetragonal structure type dominates while from x = 0.7 to the Cu₂MnGeS₄ end member the products crystallize in the orthorhombic structure type. Melting points of the mixed crystals decrease linearly with increasing manganese content.     

1,4-Diaryl and Schiff's base [1,2,3]-triazole derivative liquid crystalline compounds

Regioselective synthesis of [1,2,3]-triazoles based on the 'click-reaction', involving the Cu(I)-catalysed 1,3-dipolar cycloaddition of aryl azide to terminal arylacetylenes, was successfully employed in the preparation of two series of non-linear mesogens, based on 1,4-diaryl-[1,2,3]-triazole (Ia-e) and with Schiff's base units (IIa-c). Their mesophases were characterized by polarizing optical microscopy and differential scanning calorimetry. All final compounds exhibited preferentially the SmC phase. In addition, compounds of series I showed weak blue fluorescence in solution (λ_{max. em.} = 380-386 nm) with poor quantum yields and a Stokes shift of around 90 nm.     

Evaluation of different PAMAM dendrimers as molecular vehicle of 1,2,4-triazine N-oxide derivative with potential antitumor activity

The interaction between a 1,2,4-triazine N-oxide derivative, that holds potential antitumor activity under hypoxic conditions, and diverse polyamidoamine (PAMAM) dendrimers were investigated with the purpose of select the most appropriate macromolecule to act as potential molecular carrier of this active compound. The results shows that dendrimers with amine terminal groups (PAMAM-AT G = 3) and dendrimers with carboxylate terminal groups (PAMAM-CT G2.5 and G4.5) produces triazine derivative hydrolysis, even in buffered medium, and are not suitable as carriers. In contrast, dendrimers with neutral end groups (PAMAM-OHT) shows stable association with the active compound, making this dendrimer a possible medium for triazine carriage.     

Peierls‐Distorted Monoclinic MnB4 with a MnMn Bond

Tetraborides of chromium and manganese exhibit an unusual boron‐atom framework that resembles the hypothetical tetragonal diamond. They are believed to be very hard. Single crystals of MnB₄ have now been grown. The compound crystallizes in the monoclinic crystal system (space group P2₁/c) with a structure that has four crystallographically independent boron‐atom positions, as confirmed by ¹¹B MAS‐NMR spectroscopy. An unexpected short distance between the Mn atoms suggests a double Mn–Mn bond and is caused by Peierls distortion. The structure was solved using group‐subgroup‐relationships. DFT calculations indicate Mn^I centers and paramagnetism, as confirmed by magnetic measurements. The density of states shows a pseudo‐band gap at the Fermi energy and semiconducting behavior was observed for MnB₄.