57 Two Polymorphs of 18-Crown-6 Derivative of Phenanthro[4,5-Abc]Phenazine

Wednesday, November 4, 2009
Ballroom A+B (Camino Real Hotel)
Fadi M. Jradi , Department of Chemistry, American University of Beirut, Beirut, Lebanon
Alexandr Fonari , Department of Chemistry, New Mexico Highlands University, Las-Vegas, NM
Tatiana V. Timofeeva , Department of Chemistry, New Mexico Highlands University, Las-Vegas, NM
Mohammad H. Al-Sayah , Department of Biology and Chemistry, American University of Sharjah, Sharjah, United Arab Emirates
Bilal R. Kaafarani , Department of Chemistry, American University of Beirut, Beirut, Lebanon
ORTEP plot drawn at 50% probability level for non-hydrogen atoms (hydrogen atoms omitted)
1: a=14.554(4), b=6.6618(16), c=35.955(9)Å, β=98.116(4)o, V=3451.1(15) Å3 2: a=13.3691(6), b=14.0123(6), c=18.5477(9)Å, β=99.0420(10)o, V=3431.4(3) Å3

Organic chemosensors are molecules of abiotic nature capable to interact selectively and irreversibly with a specific substrate (ion, molecule) with corresponding changes in one or more characteristics of the system. In general a chemosensor molecule consists of a fluorophore connected to a receptor. Crown ethers, discovered by Pedersen [1], occupy a special position among receptors and are widely used in the design of new chemosensors (chromogenic, fluorescent or photoswitchable ones) based on their unique ability to bind to metal cations [2] and neutral molecules, their fairly high selectivity, and their accessibility.
A new sensor 2,7-di-tert-butyl-12,13,15,16,18,19,21,22,24,25-decahydro-[1,4,7,10,13,16]hexaoxacyclooctadeca[2,3-i]phenanthro[4,5-abc]phenazine was synthesized and its two polymorphic modifications crystallized from CH2Cl2/MeOH and CH2Cl2/hexanes (1 and 2) were studied by X-ray diffraction method. Both 1 and 2 crystallize in the same monoclinic P21/c space group with a single molecule in the asymmetric unit. The polymorphs differ by the conformation of the macrocyclic moiety. For 1 is an elliptical shape, for 2 is a heart-like shape. The transannular distances for O1...O4, O2...O6, O3...O5 are 6.054, 4.569, 4.730 Å for 1 and 5.127, 4.795, 5.567 Å for 2. Macrocycles have different sequence of torsion angles. The crystal packing patterns of the polymorphs are distinctive. The more planar shape of 1 explains its perfect stacking along the shortest b direction in the crystal with the interplane distances 3.447 Å. In crystal 2 molecules form dimers with interplane distances 3.372 Å. The calculated density of 1 is slightly lower than the calculated density of 2 (1.252 vs 1.260 Mg/m3).

References:

  1. Pedersen, C. J. J. Am. Chem. Soc.1967, 89, 2495-2496.
  2. Jradi, F. M.; Al-Sayah, M. H.; Kaafarani, B. R. Tetrahedron Lett.2008,49, 238-242.
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