Solid-state stability of Z′ < 1 and Z′ = 2 polymorphs of N,N,N′,N′-tetrabenzylethylenediamine: a combined experimental and theoretical study

Wang, Zhen, Cui, Xiaoxiao, Famulari, Antonio, Marti-Rujas, Javier, Kariuki, Benson M. ORCID: https://orcid.org/0000-0002-8658-3897 and Guo, Fang 2022. Solid-state stability of Z′ < 1 and Z′ = 2 polymorphs of N,N,N′,N′-tetrabenzylethylenediamine: a combined experimental and theoretical study. CrystEngComm 24 (45) , pp. 7924-7931. 10.1039/d2ce01174c

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Abstract

The synthesis and structural analysis by means of single crystal X-ray diffraction (SC-XRD) and DFT calculations, of two additional new polymorphs of the flexible organic molecule N,N,N′,N′-tetrabenzylethylenediamine (L) which is used as first sphere ligand in outer sphere adducts are reported. Slow crystallization of L in the solution-state yields two polymorphs (Lα-phase and Lβ-phase) with Z′ = 0.5, while fast crystallization by rapid cooling from solution and directly from melt, allows a third, less stable polymorph with Z′ = 2 (Lγ-phase). The latter structure can be seen as a low-density metastable phase obtained by trapping L molecules after they reached high mobility by thermal treatment (i.e., high energy state). The three L polymorphs have been also studied using quantum mechanical (QM) calculations specific for the solid state by comparing the sublimation energy for each polymorph, and by comparing the experimental X-ray structures against the optimized structures from DFT, showing that Lβ-phase is the most stable and Lγ-phase is the least stable phase. The high Z′ structure can be considered as a “crystal on the way” of a more stable form. These results provide insights about crystallization mechanisms and polymorphism in organic crystals. The potential use of conformational polymorphs of flexible ligands to prepare second sphere adducts with marked polymorphism is commented.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Chemistry
Publisher:	Royal Society of Chemistry
ISSN:	1466-8033
Date of First Compliant Deposit:	8 December 2022
Date of Acceptance:	21 October 2022
Last Modified:	17 May 2023 21:10
URI:	https://orca.cardiff.ac.uk/id/eprint/154750

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