A supramolecular network of 2-(4,4,5,5-tetramethyl-3-oxylimidazoline-1- oxide)-5-bromopyridine built through π-π stacking and hydrogen bonding interactions

Abstract

The X-ray study of 2-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)-5- bromopyridine (PyNN) shows an unusual 3-D supramolecular assembly formed by the combined non-covalent interactions of π-π stacking and H-bonding forces. The mean π-π stacking distance between two pyridine units is ∼3.64 Å. The angle between the plane of the pyridine ring and the stack column axis (c-axis) is 7.46°. The H-bonding distance between the oxygen atom of the water and the nitronyl nitroxide (NN) oxygen [H⋯O - N] is 1.891 Å. Two potential short N - O⋯O - N contacts are found (N - O1⋯O1-N = 3.673 Å and N - O1⋯O2 - N = 3.695 Å) along the stacked column. Four water molecules through H-bonding with four different radical oxygens form a perfect square in the a, b plane which extends as a tubular cage along the stack axis. Experimental spin densities of PyNN estimated from the 1H-NMR spectroscopy and its bulk magnetic property have been correlated with the X-ray structure in an attempt to understand the possible magnetic exchange interactions. The observed low temperature antiferromagnetic interaction is analyzed on the basis of McConnell's model I (spin polarization approach) and this magnetic behavior is probably due to the dominant N - O⋯O - N close contacts along the chain surpassing the stacking, H-bonding and other interactions. Copyright © 2006 John Wiley & Sons, Ltd.