Supramolecular Hydrogen-bonded Structures in Organic Amine Squarates
Structures of monohydrogen squarates of methylamine, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, N,N′-diemethylpiperazine and N,N,N′,N′-tetramethylguanidine have been studied in detail. The supramolecular hydrogen-bonded molecular networks are formed by the monoanion of squaric acid by itself or in association with the parent acid. Three types of hydrogen-bonded motifs are observed in these compounds, namely a liner chain, a cyclic dimer and a cyclic tetramer. These hydrogen-bonded motifs formed by the squaric acid species interact with the amine through N-H⋯O hydrogen-bonding and give rise to predominantly layered structures, while some of them also exhibit three-dimensional structures. Two of the monohydrogen squarate structures also exhibit π-π interactions between two squarate rings. The various hydrogen-bonding parameters in the amine squarates are discussed at length.
S. Mathew et al., "Supramolecular Hydrogen-bonded Structures in Organic Amine Squarates," Journal of Molecular Structure, Elsevier, Jan 2002.
The definitive version is available at http://dx.doi.org/10.1016/S0022-2860(02)00352-6
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