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Synthesis, X-ray Characterization and Density Functional Theory (DFT) Studies of Two Polymorphs of the α,α,α,α, Isomer of Tetra-p-Iodophenyl Tetramethyl Calix[4]pyrrole: On the Importance of Halogen Bonds

1
Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology (BIST), Avinguda Països Catalans, 16, 43007 Tarragona, Spain
2
Departament de Química Analítica i Química Orgànica, Universitat Rovira i Virgili, carrer Marcel•li Domingo, 1, 43007 Tarragona, Spain
3
Departament de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma de Mallorca (Baleares), Spain
4
Catalan Institution of Research and Advanced Studies (ICREA), Passeig Lluís Companys, 23, 08018 Barcelona, Spain
*
Authors to whom correspondence should be addressed.
Academic Editors: Wiktor Zierkiewicz and Steve Scheiner
Molecules 2020, 25(2), 285; https://doi.org/10.3390/molecules25020285
Received: 16 December 2019 / Revised: 3 January 2020 / Accepted: 8 January 2020 / Published: 10 January 2020
(This article belongs to the Special Issue Spectroscopic Aspects of Noncovalent Interactions)
This manuscript reports the improved synthesis of the α,α,α,α isomer of tetra-p-iodophenyl tetra-methyl calix[4]pyrrole and the X-ray characterization of two solvate polymorphs. In the solid state, the calix[4]pyrrole receptor adopts the cone conformation, including one acetonitrile molecule in its aromatic cavity by establishing four convergent hydrogen bonds between its nitrogen atom and the four pyrrole NHs of the former. The inclusion complexes pack into rods, displaying a unidirectional orientation. In turn, the rods form flat 2D-layers by alternating the orientation of their p-iodo substituents. The 2D layers stack on top of another, resulting in a head-to-head and tail-to-tail orientation of the complexes or their exclusive arrangement in a head-to-tail geometry. The dissimilar stacking of the layers yields two solvate polymorphs that are simultaneously present in the structures of the single crystals. The ratio of the two polymorph phases is regulated by the amount of acetonitrile added to the chloroform solutions from which the crystals grow. Halogen bonding interactions are highly relevant in the crystal lattices of the two polymorphs. We analyzed and characterized these interactions by means of density functional theory (DFT) calculations and several computational tools. Remarkably, single crystals of a solvate containing two acetonitrile molecules per calix[4]pyrrole were obtained from pure acetonitrile solution. View Full-Text
Keywords: polymorphs; halogen bonds; supramolecular chemistry; lattice energies; Density Functional Theory (DFT) calculations polymorphs; halogen bonds; supramolecular chemistry; lattice energies; Density Functional Theory (DFT) calculations
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Dăbuleanu, D.; Bauzá, A.; Ortega-Castro, J.; Escudero-Adán, E.C.; Ballester, P.; Frontera, A. Synthesis, X-ray Characterization and Density Functional Theory (DFT) Studies of Two Polymorphs of the α,α,α,α, Isomer of Tetra-p-Iodophenyl Tetramethyl Calix[4]pyrrole: On the Importance of Halogen Bonds. Molecules 2020, 25, 285.

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