Abstract
The four compounds, namely: 5-nitro-2-furaldehyde thiosemicarbazone (1); 5-nitro-2-thiophene thiosemicarbazone (2); 5-nitro-2-furaldehyde semicarbazone (3); and 5-nitro-2-thiophene semicarbazone (4) were synthesized and crystallized. The three new crystal structures of 1, 2, and 4 were determined and compared to three already known crystal structures of 3. Additionally, two new polymorphic forms of 1 solvate were synthesized and studied. The influence of the exchange of 2-thiophene to 2-furaldehyde as well as thiosemicarbazone and semicarbazone on the self-assembly of supramolecular nets was elucidated and discussed in terms of the formed synthons and assemblies accompanied by Full Interaction Maps analysis. Changes in the strength of IR oscillators caused by the molecular and crystal packing effects are described and explained in terms of changes of electron density.
Highlights
Knowledge about non-covalent interactions increases with each passing year [1,2,3,4,5], but is still insufficient to enable the complete design and prediction of the crystal structure of organic compounds, even with the usage of computational crystal structure prediction
The 5-nitro-2-furaldehyde thiosemicarbazone dimethylformamide solvate 1·dmfα was created during the slow evaporation of the dmf solution of 1, while 1·dmfβ was crystallized from the MeOH:dmf (1:1 v/v) solvent mixture (Table 1)
It must be outlined that the application of very specific conditions such as high pressure can hypothetically lead to the formation of other polymorphic forms, but any evidence of the formation of other than the described forms was not registered during the study
Summary
Knowledge about non-covalent interactions increases with each passing year [1,2,3,4,5], but is still insufficient to enable the complete design and prediction of the crystal structure of organic compounds, even with the usage of computational crystal structure prediction. The hydrogen bond rules [8,9], exchange rule [10,11], synthon hierarchy for some functional group [12,13,14,15,16], and molecular tectonics [17,18,19] are the most important principles among all of the studied ones. They are very helpful in predicting the results of crystal formation, but are still insufficient. Better understanding of the nature of intermolecular interactions and the ability to foresee the molecular structure are the key aspects for the engineering and control of crystal packing and, the physical and chemical properties
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