Unusual coordination behavior by a hydroxypyridine/pyridone ligand: Synthesis and structure of [(2-bromo-4-hydroxypyridine)2(2-bromo-1(H)-4-pyridone)2copper(II)] perchlorate • 2(2-bromo-4-hydroxypyridine) • 2(2-bromo-1(H)-4-pyridone)

Thermal and Emission Properties of a Series of Lanthanides Complexes with N-Biphenyl-Alkylated-4-Pyridone Ligands: Crystal Structure of a Terbium Complex with N-Benzyl-4-Pyridone

This work focuses on the investigation of the liquid crystalline behavior and luminescence properties of the lanthanide complexes of Eu(III), Sm(III) and Tb(III) with N-biphenyl-alkylated-4-pyridone ligands. The organic ligands having a biphenyl group attached via a long flexible spacer with either 9 or 10 carbon atoms were synthesized by the reaction between 4-hydroxypyridine and the corresponding bromide compounds. The chemical structures of the organic and lanthanide complexes were assigned based on elemental analysis, single-crystal X-ray diffraction, ¹H, ¹³C NMR and IR spectroscopies, and thermogravimetric analysis (TGA). The X-ray diffraction analysis of a parent compound shows that the lanthanide ions are surrounded by three monodentate pyridone ligands and three bidentate nitrate ions, giving a 9-coordinate environment. The mesogenic behavior and the type of liquid crystalline phases exhibited by the new complexes were analyzed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM), and powder X-ray diffraction (XRD) studies. Only the lanthanide complexes with longer spacer (10) display a monotropic SmA phase, typically on a short thermal range (less than 10 °C). The complexes with shorter flexible chains (9) show no liquid crystalline properties with melting temperatures lower than their analogs with longer spacers. The emission spectra recorded in solid state at room temperatures show typical emission bands for each lanthanide ion employed (Eu(III), Tb(III) and Sm(III)).

Pyridazinones from maleic hydrazide: a new substrate for the Mitsunobu reaction

Crystal engineered organic frameworks assembled using hydrogen bonding are known, and examples constructed from hydroxypyridine/pyridone as the dominant source of hydrogen bonding have been reported. Less explored are analogous systems based on maleic hydrazide. Herein, a two-step route (Mitsunobu followed by Schiff base reactions) to asymmetrically substituted pyridazinones from maleic hydrazide (step 1) is reported with 2-, 3-, or 4-pyridinecarboxaldehyde (step 2). Upon reaction with 4-pyridinecarboxaldehyde, single crystals suitable for analysis via X-ray diffraction were obtained. Careful examination of this solid state structure and comparison with a large number of related structures in the Cambridge Structural Database revealed a pyridazinone (vs. pyridazinol) core and persistent [Formula: see text] “head-to-tail” hydrogen bonded dimers. Although these pyridazinones were originally considered suitable for use as ligands for metal cation coordination, challenges in achieving this outcome were encountered.