Influence of N-heteroaromatic π–π stacking on supramolecular assembly and coordination geometry; effect of a single-atom change in the ligand

Abstract

In order to understand how the polarization of aromatic systems, through the introduction of a nitrogen heteroatom, affects the π-π interactions and crystal packing of mercury coordination compounds, in this study, N-(quinolin-2-yl)pyrazine-2-carboxamide and N-(quinolin-3-yl)pyrazine-2-carboxamide ligands were employed in the synthesis of five Hg(II) complexes, [HgBr2(L2=quin)2]n, 1, [HgI2(L2=quin)], 2, [HgCl2(L3=quin)]n, 3, [Hg3Br6(L3=quin)2]n, 4, and [Hg3I6(L3=quin)2]n, 5. X-ray single crystal diffraction analysis of these compounds revealed that all the complexes have polymeric structures except complex 2, which is a discrete compound. Complexes 1 and 3 have 1D and 2D polymeric structures, respectively, while complexes 4 and 5 are 3D coordination polymers. In comparison to homologous complexes containing the N-(naphthalene-2-yl)pyrazine-2-carboxamide ligand, L2=naph, interestingly, the structural analysis clearly shows that the replacement of the naphthyl CH group with a nitrogen atom changes the spatial extent of the π-electron cloud and the polarity of the aromatic ring, from L2=naph adducts to L2=quin and L3=quin adducts, and the propensity to form π-π interactions increases. These π-π stacking interaction synthons affect the coordination geometry and structural assembly. This study reveals the undeniable contribution of π-π stacking interactions to the organization and stabilization of some of the crystal structures reported here.

First Report on Crystal Engineering of Hg(II) Halides with Fully Substituted 3,4-Pyridinedicarboxamides: Generation of Two-Dimensional Coordination Polymers and Linear Zig-Zag Chains of Mercury Metal Ions

“…In order to explore the effect of π-π interaction on the crystal packing of the complex 4 and complex 5 containing ligand L 2 , we have calculated the geometrical parameters that account for the amount of slippage of the two pyridine rings involved in π-π interactions. 91 These geometric parameters were calculated for 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 19 all complexes but only isostructural complexes, 4 and 5 showed these interactions at reasonable Cg-Cg distances 90 as shown in Fig. 10b-c and given in Table S2(ESI).…”

Toward Novel [18F]Fluorine-Labeled Radiotracers for the Imaging of α-Synuclein Fibrils

“…This could be attributed to the energy costs of desolvation, since a donated H-bond requires nearly twice the energy of an accepted one to be broken (Polêto et al, 2018). Lastly, a higher predisposition to the formation of π-π interactions upon the replacement of a methylidene carbon in the ring with a nitrogen atom, which ultimately improves affinity to α-syn (Huber et al, 2014;Khavasi et al, 2015)] was seen in the 6-fluoropyridine DABTAs and d 4 .…”

Controlling π–π Interactions through Coordination Bond Formation: Assembly of 1-D Chains of acac-Based Coordination Compounds

“…A careful examination of the reported crystal networks shows that there are Cl···Hg, Br···Hg, and O···Hg interactions that can be responsible for bringing together the aromatic rings (Figure ). Khavasi reported these long coordination bonds for similar compounds, − and Puddephatt and his group reported a series of Hg­(II) coordination compounds which reveal that long coordination bonds direct the assembly of coordination polymers . Therefore, the closeness of aromatic rings in the crystal networks is not necessarily due to an attractive interaction between them.…”