Abstract
In a series of salts of ethane-1,2-diamine with acetic (1), trifluoroacetic (2), trichloroacetic (3), and dichloroacetic (4) acids, the amine is doubly protonated so the cation:anion stoichiometry is 2:1. In 1 and 2, dications are lying across the center of symmetry (Z′ = 1/2), in 4 dication is nonsymmetric (Z′ = 1), while the structure of 3 contains both symmetric and nonsymmetric cations (Z′ = 3/2). All dications, either symmetric or not, are in extended (trans) form, by far the most popular among the salts of ethane-1,2-diamine. Strong hydrogen N–H···O bonds constitute the main specific, directional force determining the crystal packing. In 1, one of the N–H hydrogen atoms is involved in bifurcated hydrogen bonds, and in this case, four alresaacceptor oxygen atoms are almost equally involved in accepting the hydrogen bonds; in consequence, the C–O bond lengths are almost equal. In all other cases, the C–O bonds with oxygen atoms involved in more hydrogen bonds are systematically longer than those which accept less such interactions. Halogen C–Cl···O interactions are observed in two (out of five) symmetry-independent anions of 3 and 4, suggesting that at least in this series, the roles of these interactions are only secondary in nature. No significant involvement of fluorine atoms in directional interactions is detected, however. The hydrogen-bond networks are described by means of graph-set method. In addition, Hirshfeld surfaces are used to detect and visualize the differences between similar moieties, and fingerprint plots are presented in order to analyze the mutual importance of different kinds of interactions.
Highlights
The disposition of molecules in the molecular crystals is determined by the fine equilibrium between a number of competing factors, among others the tendency toward close packing, the requirements of the space group of symmetry, interplays between different intermolecular interactions, conformational freedom, etc. (e.g., [1, 2])
There are often more than one possible disposition of molecules, which reflect in the phenomenon of polymorphism, and show the level of complication for the attempts of predicting crystal structures ([3], and references therein)
We present the analyses of the crystal structures and packing modes for a series of salts of the simplest member of this family—ethane-1,2-diamine
Summary
The disposition of molecules (or molecular ions) in the molecular crystals is determined by the fine equilibrium between a number of competing factors, among others the tendency toward close packing, the requirements of the space group of symmetry, interplays between different intermolecular interactions, conformational freedom, etc. (e.g., [1, 2]). We have studied the packing modes of simple salts of α,ω-diaminoaliphatic alkanes (linear molecules with hydrogen-bond donors located at the ends of the chain) with acetic acid and its mono- di-, and trichloro. J IRAN CHEM SOC (2015) 12:2115–2123 derivatives, which provide the acceptors for hydrogen bonds as well as the possibility of halogen-bonding interactions (for instance, [4, 5]) In these cases, we have determined that the potential halogen bonds or N–H···Cl hydrogen bonds do not compete successfully with the N–H···O hydrogen bonds of different strengths which—certainly along with the coulombic interactions between the charged. We present the analyses of the crystal structures and packing modes for a series of salts of the simplest member of this family—ethane-1,2-diamine.
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