The Oxamate Anion: A Flexible Building Block of Hydrogen-Bonded Architectures for Crystal Engineering

In order to examine the possibilities of using the oxamate anion,
[OOCCONH2]-, as a versatile
building
block of low-dimensional, hydrogen-bonded scaffolding, the preferential
assembly patterns displayed by this anion
were identified using X-ray single-crystal data for a sequence of
simple oxamate salts. Several new compounds
were synthesized, and the crystal structures of six materials are
presented:  piperidinium oxamate (1),
2-amino-5-nitropyridine 2-amino-5-nitropyridinium oxamate (2),
imidazolium oxamate (3), (4-chlorobenzyl)ammonium
oxamate
(4), (3-chlorobenzyl)ammonium oxamate (5),
and potassium oxamate monohydrate (6). The oxamate
anion acts as
a building block of either 1-D (ribbons or ladders) or 2-D (layers)
motifs. These architectures (generated by
NH···O
hydrogen bonds) are the result of the selectivity of complimentary
hydrogen-bond sites of the anion. However, the
type of network adopted is also influenced by cation−anion
interactions, and the role of the physical−chemical
characteristics of the cation in inducing a specific anionic motif, is
discussed. The oxamate anion, as well as other
deprotonated carboxylic amides, may represent useful additions to the
existing collection of building blocks capable
of generating extended hydrogen-bonded motifs for crystal
engineering.