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

Steric control of supramolecular association in structures of Zn(S2COR)2withN,N′-bis(pyridin-4-ylmethyl)oxalamide

“…Overall, each 4 LH2 molecule has an anti-periplanar conformation as is found in the two polymorphs of the uncoordinated molecule [34,35]. Finally, it is noted the central amide-C-C(amide) bond lengths (Table 2) are longer than usually anticipated C(sp 2 )-C(sp 2 ) bonds, an observation related to the presence of electronegative groups bound to these atoms, as discussed in the literature [18]. As each of the 4 LH2 molecules is bidentate bridging, a coordination polymer is generated, Figure 3.…”

“…a diamide link as in N,N'-bis(pyridin-4-ylmethyl)ethanediamide ( 4 LH2), as shown in Figure 1. The structural chemistry of the isomeric N,N'-bis(pyridin-n-ylmethyl)ethanediamides, n LH2 for n = 2, 3 and 4, has also been reviewed in recent times [18]. With potential for supramolecular aggregation via hydrogen [19] and halogen [20] bonding, often leading to two-dimensional arrays, these molecules featured prominently in the pioneering days of crystal engineering.…”

Unusual {⋯HNC2O⋯HCnO}, n = 1 or 2, synthons predominate in the molecular packing of one-dimensional coordination polymers, {Cd[S2P(OR)2]2(3LH2)}n, for R = Me and Et, but are precluded when R = i-Pr; 3LH2 = N,N′-bis(3-pyridylmethyl)oxalamide

“…Thus, the presence of the central oxalamide moiety offers opportunities for the formation of supramolecular tapes 1 while pyridyl-N atoms are highly prone to associate with different organic residues such as carboxylic acids 2 and are ideal for coordination to a wide variety of metal centres. 3 As highlighted in a recent bibliographic review, 4 all of these possibilities have been realised although studies with these molecules are relatively limited in consideration of the supramolecular association opportunities patently available and in recognition of their relatively straightforward synthesis. 5,6 A highlight from the (relatively) early literature of n LH 2 is the assembly of 3 LH 2 and N,N′-dicarboxymethylurea mole-cules into a two-dimensional array in a 1 : 1 co-crystal through a combination of 10-membered amide synthons, {⋯HNC 2 O} 2 , and six-membered {⋯O⋯HNCNH} synthons, respectively, with the connections between the parallel tapes being of the type carboxylic acid-O-H⋯NIJpyridyl).…”

“…7 The n LH 2 molecules also featured in early systematic studies in halogen bonding. 4 For example, the 1 : 1 co-crystal formed between 3 LH 2 and 1,4-di-iodobuta-1,3-diyne, features supramolecular tapes formed by 3 LH 2 , mediated by 10-membered amide {⋯HNC 2 O} 2 synthons, being cross-linked by I⋯N halogen bonding within a two-dimensional array. 8 In terms of interacting with metal centres, 3 LH 2 , for example, has been shown to bridge two ZnijS 2 CNIJMe)CH 2 CH 2 OH] 2 molecules via Zn-NIJpyridyl) dative bonding, which, through conventional hydroxyl-O-H⋯OIJhydroxyl) hydrogen bonding, was assembled to interwoven double chains.…”