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

Abstract

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.The structural analysis of the terpyridine-based compound (ITPH3)2[ZnCl4]3·H2O [(ITPH3)3+ is the triply protonated cation of 4′-(isoquinolin-4-yl)-2,2′:6′,2′′-terpyridine] demonstrates the concerted way in which a variety of noncovalent interactions, viz. hydrogen bonding, π-π and anion...π, participate in the crystal packing. An unexpected large enrichment ratio between the cationic C...N contacts can be understood in the light of their correlation with the atomic and ring NBO (natural bond order) charges.