Leopoldo Suescun

Synthesis and structural characterization of LaxSr1−xMnO2.6+δ (0.1<x<0.4) compounds displaying compressed octahedral coordination of Mn(4−5x)+

La{sub x}Sr{sub 1-x}MnO{sub 2.6+{delta}} (x=0.1-0.4) compounds have been obtained by low-temperature annealing of stoichiometric materials in hydrogen. La{sub 0.1}Sr{sub 0.9}MnO{sub 2.6+{delta}} ({delta}=0.15) and La{sub 0.3}Sr{sub 0.7}MnO{sub 2.6}, tetragonal (P4/m), and La{sub 0.2}Sr{sub 0.8}MnO{sub 2.6}, pseudo-tetragonal monoclinic (P2/m), structures are isostructural with oxygen-vacancy-ordered Sr{sub 5}Mn{sub 5}O{sub 13} (a = b {approx} {radical}5a{sub p}, c {approx} a{sub p}). La{sub 0.4}Sr{sub 0.6}MnO{sub 2.6} shows cubic perovskite structure with disordered oxygen vacancies. In the vacancy-ordered (La{sub x}Sr{sub 1-x}){sub 5}Mn{sub 5}O{sub 13} phases four out of five Mn cations are Mn{sup 3+} and show a typical Jahn-Teller elongated pyramidal coordination while the fifth one Mn{sup (4-5x)+}, in octahedral environment, shows decreasing formal charge from Mn{sup 4+} (x=0) to Mn{sup 2.5+} x=0.3. This unusual selective doping of the octahedral site produces structural strain due to increasing size of the Mn{sup (4-5x)+} and, in the case of (La{sub 0.2}Sr{sub 0.8}){sub 5}Mn{sub 5}O{sub 13}, the unusual compressed octahedral arrangement of oxygen atoms around it. The coordination geometry implies that either the d{sub x{sup 2}-y{sup 2}} orbital is occupied, which would be a rare example of inverted occupancy of e{sub g} orbitals in manganites, or that disordered Mn{sup 3+} apically elongated MnO{sub 6} octahedra are present with normal electronicmorexa0» configuration d{sub 1{sub 2{sub g}}}{sup 3}d{sub x{sup 2}-y{sup 2}}{sup 0}d{sub z{sup 3}}{sup 1}, and the observed bond distances are the average of the long and intermediate in-plane Mn-O bonds. Several structural features favor the second case.«xa0less

Crystal structures of five new substituted tetrahydro-1-benzazepines with potential antiparasitic activity.

Tetrahydro-1-benzazepines have been described as potential antiparasitic drugs for the treatment of chagas disease and leishmaniasis, two of the most important so-called `forgotten tropical diseases affecting South and Central America, caused by Trypanosoma cruzi and Leishmania chagasi parasites, respectively. Continuing our extensive work describing the structural characteristics of some related compounds with interesting biological properties, the crystallographic features of three epoxy-1-benzazepines, namely (2SR,4RS)-6,8-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (1), (2SR,4RS)-6,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (2), and (2SR,4RS)-8,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (3), all C22H21NO, and two 1-benzazepin-4-ols, namely 7-fluoro-cis-2-[(E)-styryl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C18H18FNO, (4), and 7-fluoro-cis-2-[(E)-pent-1-enyl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C15H20FNO, (5), are described. Some peculiarities in the crystallization behaviour were found, involving significant variations in the crystalline structures as a result of modest changes in the peripheral substituents in (1)-(3) and the occurrence of discrete disorder due to the molecular overlay of enantiomers with more than one conformation in (5). In particular, an interesting phase change on cooling was observed for compound (5), accompanied by an approximate fourfold increase of the unit-cell volume and a change of the Z value from 1 to 4. This transition is a consequence of the partial ordering of the pentenyl chains in half of the molecules breaking half of the -3 symmetry axes observed in the room-temperature structure of (5). The structural assembly in all the title compounds is characterized by not only (N,O)-H...(O,N) hydrogen bonds, but also by unconventional C-H...O contacts, resulting in a wide diversity of packing.