Structural characterization of a hybrid terpyridine-pyrazine ligand and its one-dimensional ZnII coordination polymer: a computational approach to conventional and nonconventional intermolecular interactions.

The structures of a new hybrid terpyridine-pyrazine ligand, namely 4'-[4-(pyrazin-2-yl)phenyl]-4,2':6',4''-terpyridine (L2), C25H17N5, and its one-dimensional coordination polymer catena-poly[[bis(acetylacetonato-κ2O,O')zinc]-µ-4'-[4-(pyrazin-2-yl-κN4)phenyl]-4,2':6',4''-terpyridine-κN1], [Zn(C5H7O2)2(C25H17N5)]n or [Zn(acac)2(L2)]n (Hacac is acetylacetone), are reported. Packing interactions in both crystal structures are analyzed using Hirshfeld surface and enrichment ratio techniques. For the simpler structure of the monomeric ligand, further studies on the interaction hierarchy using the energy framework approach were made. The result was a complete picture of the intermolecular interaction landscape, which revealed some subtle details, for example, that some weak (at first sight negligible) C-H...N interactions in the structure of free L2 play a relevant role in the crystal stabilization.

Crystallographic and computational study of a network composed of [ZnCl4]2- anions and triply protonated 4'-functionalized terpyridine cations.

We report herein the synthesis, crystallographic analysis and a study of the noncovalent interactions observed in the new 4'-substituted terpyridine-based derivative bis[4'-(isoquinolin-2-ium-4-yl)-2,2':6',2''-terpyridine-1,1''-diium] tris[tetrachloridozincate(II)] monohydrate, (C24H19N4)2[ZnCl4]3·H2O or (ITPH3)2[ZnCl4]3·H2O, where (ITPH3)3+ is the triply protonated cation derived from 4'-(isoquinolin-4-yl)-2,2':6',2''-terpyridine (ITP) [Granifo et al. (2016). Acta Cryst. C72, 932-938]. The (ITPH3)3+ cation presents a number of interesting similarities and differences compared with its neutral ITP relative, mainly in the role fulfilled in the packing arrangement by the profuse set of D-H...A [D (donor) = C, N or O; A (acceptor) = O or Cl], π-π and anion...π noncovalent interactions present. We discuss these interactions in two different complementary ways, viz. using a point-to-point approach in the light of Bader's theory of Atoms In Molecules (AIM), analyzing the individual significance of each interaction, and in a more `global' analysis, making use of the Hirshfeld surfaces and the associated enrichment ratio (ER) approach, evaluating the surprisingly large co-operative effect of the superabundant weaker contacts.