The unusual (syn-/anti-)2 conformation of a dimethoxypyrimidyl-based tennimide

Abstract

The tennimide macrocycle, (I) (C52H40N16O16.0.167H2O), was synthesized from 2-amino-4,6-dimethoxypyrimidine and pyridine-2,6-dicarbonyl dichloride. Compound (I) represents the first tennimide incorporating pyridine rings in the macrocycle scaffold. In the macrocycle ring, the carbonyl groups at each successive dicarbonyl(pyridine) moiety adopt the (syn/anti)2 conformation. This contrasts with all previously reported tetraimide macrocycles, which exhibit the (syn)4 conformation. The effect is to close any potential cavity or niche by having two of the central pyridine C5N rings aligned close to each other [with closest pyridine Cg...Cg ring centroid separations of 3.5775 (19) Å; closest C...C = 3.467 (5) Å]. A partial occupancy water molecule (with s.o.f. = 0.167), resides with its oxygen atom on a twofold axis at hydrogen-bonding distances to the carbonyl O atom, in a molecular niche between two pyridine rings. Macrocyles of (I) have all six C=O groups and all eight methoxy O atoms present on the macrocycle surface. However, all twelve N atoms are effectively shielded on steric grounds from any potential intermolecular interactions. The remaining two C=O O atoms interact with the partial occupancy water molecule via two O—H...O=C hydrogen bonds. Macrocycles of (I) stack as one-dimensional chains along the b-axis direction with primary intermolecular interactions involving weak C—H...O=C/OCH3/H2O contacts. Chains interlock weakly via methoxy–methoxy C—H...O interactions into two-dimensional sheets.

Keywords

• conformation
• macrocycle
• methoxy
• pyridine
• pyrimidine
• tennimide
• tetramer
• crystal structure