A supramolecular network of 2-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)-5-bromopyridine built throughπ-πstacking 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.