Two New Supramolecular Compounds that Involve Trans-1,2-bis(4- pyridyl)ethylene (bpe), Barbituric Acid and Fe(II) ions

Abstract

In this study, the synthesis, spectroscopic properties (infrared and Raman) and crystal structures of two new compounds named (H2bpe)B2 . 2H2O (1) and (Fe(bpe)(H2O)4)B2·4H2O (2) have been reported, where bpe is trans-1,2- bis(4-pyridil)-ethylene, H2bpe is protonated bpe and B - is the barbiturate anion. For both complexes, we observed the presence of supramolecular interactions, such as electrostatic, hydrogen bonding and � -stacking interactions. Compound 1 crystallised in a triclinic system with the space group P-1, which was generated by cationic and anionic units formed by protonated bpe, the barbiturate anion and water molecules. These molecules interacted through weak intermolecular inter- actions and were responsible for the crystalline stability of the synthesised compounds. For compound 2, an orthorhombic crystal system was observed with a Pbcn space group. In this crystal, the metallic site adopted a distorted octahedral ge- ometry that was coordinated by two pyridine nitrogen atoms and four oxygen atoms from coordinated water molecules. The three-dimensional arrangement of the structure consisted of one covalent one-dimensional linear cationic (Fe(bpe)(H2O)4) 2+ chain, which interacts by forming hydrogen-bonding, � -stacking and electrostatic interactions with bar- biturate anions and water molecules that were trapped in the crystal. The vibrational spectra of the two compounds were very similar despite the different crystalline arrangements that were adopted by the two structures. In the infrared spectra, two intense bands at 1684 and 1630 cm -1 were observed and assigned to the CO stretching ( CO) of the barbiturate anion and  C=C of the bpe ligand, respectively. In the Raman spectra of the compounds, the most important bands were attrib- uted to the bpe ligand at 1629 and 1006 cm -1 , which were assigned to the  C=C and  ring, respectively. The presence of the barbiturate anion was confirmed by the presence of a band of low intensity located at 680 cm -1 and was assigned as the