Anion–Anion Interactions in the Crystal Packing
of Functionalized Methanide Anions: An Experimental and Computational
Study
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Abstract
Examination
of the crystal structures of (Me<sub>4</sub>N)(dcnm)
(<b>1</b>), (Me<sub>4</sub>N)(dcnom) (<b>2</b>), and (Me<sub>4</sub>N)(nbdm) (<b>3</b>) [dcnm = dicyanonitrosomethanide,
dcnom = dicyanonitromethanide, nbdm = nitroso-<i>N</i>,<i>N</i>-bis(dicyanomethanide)] reveals the anions pack in an unusual
columnar array, with distances between the planar species suggestive
of π–π stacking. This columar packing motif is
not observed in the crystal structures of (Me<sub>4</sub>N)(ccnm)
(<b>4</b>) and (Me<sub>4</sub>N)(ccnom) (<b>6</b>) (ccnm
= carbamoylcyanonitrosomethanide, ccnom = carbamoylcyanonitromethanide),
in which hydrogen bonding between anions is the dominant supramolecular
interaction. Ab initio calculations performed at the HF and MP2 levels
of theory on ionic clusters of varying size further explored the nature
and strength of anionic interactions observed in crystal structures.
The first syntheses of the nbdm and ccnom anions are also reported
