Abstract
A crystal structure determination of 2, 2′-bipyrroyl (1; 2, 2′-dipyrryl-diketone, bis (2-pyrrolyl)ethanedione) and its spectroscopic properties in solution are reported. In the crystal, 1 self-assembles via hydrogen bonding into supramolecular ribbons that extend indefinitely through the crystal lattice. The observed molecular conformation is one where each pyrrole ring and adjacent carbonyl group are co-planar (torsion angle ∼0.9°), with the N-H pointing in the same direction as the C=O. The two carbonyls have a transoid but not co-planar geometry with a torsion angle of ∼128°. Adjacent molecules in the crystal are linked by pairs of intermolecular hydrogen bonds, pyrrole NH to carbonyl oxygen, to form a matrix of polymeric chains that lie like neatly stacked, parallel streams of ribbons. Molecular mechanics calculations on the monomer indicate an intra-molecularly hydrogen bonded planar conformation (sp, ap, sp) at the global energy minimum. In CHCl3, 1 is monomeric according to vapor pressure osmometry (MWobs = 179±10 vs · MWcale = 188). In THF, the measured molecular weight is 340±15, which corresponds best to one molecule of 1 solvated by two THF molecules (MW= 322 for C10H8N2O4 · 2 C4H8O) rather than to a dimer.
Original language | English |
---|---|
Pages (from-to) | 239-249 |
Number of pages | 11 |
Journal | Monatshefte fur Chemie |
Volume | 131 |
Issue number | 3 |
DOIs | |
State | Published - 2000 |
Externally published | Yes |
Scopus Subject Areas
- General Chemistry
Keywords
- Conformational analysis
- Hydrogen bonding
- Pyrrole
- α-Diketone