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The combinatorial chemistry approach has been used to synthesize an array of Schiff bases. The structures of five of these Schiff bases have been confirmed by X-ray analysis [Nesterov, Timofeeva, Borbulevych, Antipin & Clark (2000). Acta Cryst. C 56, 971-975]. In two cases, the reaction conditions were not sufficient to obtain the products in question. In one case, a molecular complex, C10H10O2·­C6H5N3O4, of the starting products 4-methoxy­cinnam­aldehyde and 2,4-di­nitro­aniline was found. X-ray analysis revealed hydrogen-bond formation between the mol­ecules of these reagents in the crystal. In the other case, X-ray analysis demonstrated that no chemical reaction occurred under the reaction conditions, and only one starting reagent, 4-(di­methyl­amino)­cinnam­aldehyde, C11H13NO, was found in the precipitate. [ABSTRACT FROM AUTHOR]

The crystallization behavior of the title compound, [Co(C2H8N2)3](C2O4)(ClO4)·2H2O, has been studied in order to evaluate the effect of the counter-anion on the crystalline structures of [Co(en)3](C2O4)· X (en = ethyl­enedi­amine). Two-dimensional intermolecular hydrogen-bonding networks are formed between the amine protons of the [Co(en)3]3+ cations and the O atoms of the oxalate anions. Perchlorate and water mol­ecules fill in the channels between the two-dimensional networks and form hydrogen-bonding interactions with the two-dimensional layers, thus constructing a three-dimensional hydrogen-bonding network. [ABSTRACT FROM AUTHOR]

The title compound, C17H14O4, is an unprecedented new synthetic isoaurone-type enol ether that has the E configuration. The planar furanone ring is fused to a methoxy­benzene ring system, with an interplanar angle of 175.7 (1)°. Due to this ring fusion, the six-membered ring has a significant amount of ring strain, as shown by the internal ring angle range of 115.8 (1)-124.7 (1)°, whereas the vinylic phenyl ring has internal angles between 119.7 (1) and 120.2 (1)°. The mol­ecules form infinite hydrogen-bonding layers along the b direction of the form C-H⋯O, where the keto O atom acts as a bifurcated acceptor. These layers are connected along the c direction by another hydrogen bond with a methoxy H atom as donor. In addition to this connection, the layers are stacked via centres of symmetry by a pair of symmetry-related benzo­furan­one ring systems. [ABSTRACT FROM AUTHOR]

A new `rule' for the association of hydrogen-bond donors and acceptors in crystal structures is presented. It implies that ranks are assigned to each donor and each acceptor (1 is best, 2 is next best etc.), and that hydrogen bonds should be formed between donors and acceptors in rank order. l-Ser- l-Ala, C6H12N2O4, is used together with its retroanalogue, l-Ala- l-Ser, and three other pairs of dipeptide retroanalogues to illustrate this rule and the reasons why it may not always be followed. [ABSTRACT FROM AUTHOR]