Structural, Hirshfeld surface and theoretical analysis of two conformational polymorphs of N,N′-bis(pyridin-3-ylmethyl)oxalamide

Abstract

The common feature of two conformational polymorphs of

Perplexing Coordination Behaviour of Potentially Bridging Bipyridyl-Type Ligands in the Coordination Chemistry of Zinc and Cadmium 1,1-Dithiolate Compounds

“…In contrast to 42, the NS 4 coordination geometry in 43 is based on a trigonal-pyramid with τ = 0.76. While such remarkable differences in conformation may seem incongruent, computational chemistry performed on 3-pdaO show that the energy difference between the extended form, where the 3-pyridyl rings are anti-periplanar, and the curved form, where the rings are syn-periplanar, is less than 1 kcal/mol [71]. This observation highlights the conformational flexibility of this class of molecule and their related thioamide derivatives [72].…”

13. Crystal chemistry of the isomeric N,N'-bis(pyridin-n-ylmethyl)-ethanediamides, n = 2, 3 or 4

“…The diamide moiety is usually strictly planar with rarely only minor deviations apparent. The arrangement is always anti-periplanar facilitating the formation of intramolecular amide-N-H…O(amide) hydrogen bonds; calcula-tions (DFT) show alternate arrangements are over 6 kcal mol -1 less stable [8]. Finally, being attached to two electronegative substituents, the amide-C-C(amide) bond is usually longer than anticipated for an sp 2 -C-C(sp 2 ) bond [5].…”

“…The di-cations associate into a supramolecular tape with translational symmetry via a sequence of amide {…HNC2O}2 synthons akin to that shown in Fig. 3a for Form I of 3 LH2 [8]. As illustrated in Fig.…”

“…While the crystal structure of 2 LH2 has yet to be reported, two polymorphs are known for each of 3 LH2 [8] and 4 LH2 [9,10]. The dithiodiamide analogue of 2 LH2 has been described and based on the experimental and theoretical (DFT) structures it was suggested that an all planar conformation located about a centre of inversion is most stable owing to the presence of intramolecular amide-N-H…N(pyridyl) hydrogen bonding [7].…”

“…centrosymmetric planar, applies to 2 LH2. The two polymorphs of 3 LH2 have only just recently been described [8], and each crystallises in the monoclinic space group P21/c. In Form I, one entire molecule comprises the asymmetric unit, i.e.…”