Can Stacking Interactions Exist Beyond the Commonly Accepted Limits?

Abstract

Systematic study of π-π interactions of structurally characterised compounds containing parallel benzene and/or pyridine rings was carried out. The gathered geometrical parameters were analysed in statistical terms. The quantum mechanical calculations were made for the above mentioned ring systems in different arrangements and the calculated interaction energy values were referred to the statistical data. The maximum bonding energy of the studied systems is about 3 kcal/mol. The ring rotation about the vertical axis has almost no influence on the system binding energy. In the specific ring arrangements, the stacking interactions can be bonding even for ring centroids distances larger than 6 Å. The results prove that the appliance of the generally accepted geometrical criteria of stacking interactions leads to the omission of the multiple bonding intermolecular interactions during the interpreting of the reactivity, self assembly as well as the properties of the supramolecular compounds. AbstractSystematic study of π-π interactions of structurally characterised compounds containing parallel benzene and/or pyridine rings was carried out. The gathered geometrical parameters were analysed in statistical terms. The quantum mechanical calculations were made for the above mentioned ring systems in different arrangements and the calculated interaction energy values were referred to the statistical data. The maximum bonding energy of the studied systems is about 3 kcal/mol. The ring rotation about the vertical axis has almost no influence on the system binding energy. In the specific ring arrangements, the stacking interactions can be bonding even for ring centroids distances larger than 6 Å. The results prove that the appliance of the generally accepted geometrical criteria of stacking interactions leads to the omission of the multiple bonding intermolecular interactions during the interpreting of the reactivity, self assembly as well as the properties of the supramolecular compounds.

The intricacies of the stacking interaction in a pyrrole–pyrrole system

“…Hence, this conformation is not energetically favourable and should not be arbitrarily used in studies of pÁÁÁp interactions. This is in accordance with the study made for other systems [17,81].…”

“…However, the bonding geometry boundaries are relatively broad, and the stacking interactions can be binding even for ring centroid distances larger than 6 Å , provided that the stacked rings are in an appropriate geometry. Recently, the same has been observed for sixmembered aromatic ring systems [81][82][83].…”

Trinuclear Co(II) and Mononuclear Ni(II) Salamo-Type Bisoxime Coordination Compounds

“…Although the Co(II) atoms are all hexa-coordinated, the coordination sphere of the Co1 atom consists of six oxygen atoms, and that of the Co2 (or Co2 #1 ) atom includes two nitrogen and four oxygen atoms. In coordination compound 1, six pairs of intramolecular hydrogen bond (C2-H2···O2, C8-H8B···O7, C10-H10B···O3, C10-H10B···O6, C16-H16···O5 and C20-H20C···O5) [68] interactions involving one phenoxo oxygen, one coordinated acetone, two acetate ions, and alkoxy O atoms in each molecule (Figure 4) and the weak hydrogen bonds existing in the coordination compound 1 are described in graph sets ( Figure 5) [69], A pair of π⋯π interactions (Cg1⋯Cg2 (Cg1=C1-C2-C3-C4-C5-C6 and Cg2=C12-C13-C14-C15-C16-C17)) ( Figure 6) were formed [70]. In coordination compound 1, six pairs of intramolecular hydrogen bond (C2-H2···O2, C8-H8B···O7, C10-H10B···O3, C10-H10B···O6, C16-H16···O5 and C20-H20C···O5) [68] interactions involving one phenoxo oxygen, one coordinated acetone, two acetate ions, and alkoxy O atoms in each molecule (Figure 4) and the weak hydrogen bonds existing in the coordination compound 1 are described in graph sets ( Figure 5) [69], A pair of π· · · π interactions (Cg1· · · Cg2 (Cg1=C1-C2-C3-C4-C5-C6 and Cg2=C12-C13-C14-C15-C16-C17)) ( Figure 6) were formed [70].…”

“…In coordination compound 1, six pairs of intramolecular hydrogen bond (C2-H2···O2, C8-H8B···O7, C10-H10B···O3, C10-H10B···O6, C16-H16···O5 and C20-H20C···O5) [68] interactions involving one phenoxo oxygen, one coordinated acetone, two acetate ions, and alkoxy O atoms in each molecule (Figure 4) and the weak hydrogen bonds existing in the coordination compound 1 are described in graph sets ( Figure 5) [69], A pair of π⋯π interactions (Cg1⋯Cg2 (Cg1=C1-C2-C3-C4-C5-C6 and Cg2=C12-C13-C14-C15-C16-C17)) ( Figure 6) were formed [70]. …”

Unprecedented Hexanuclear Cobalt(II) Nonsymmetrical Salamo-Based Coordination Compound: Synthesis, Crystal Structure, and Photophysical Properties

“…In addition, there is a pair of π···π interactions Cg1···Cg1 (Cg1=C1-C2-C3-C4-C5-C6) (Figure 3) in the Co(II) coordination compound [79]. Meanwhile, the hydrogen bonds interactions existing in the Co(II) coordination compound are described in graph sets (Figure 4) [80].…”