Symmetry-Dependent Intermolecular π–π Stacking Directed by Hydrogen Bonding in Racemic Copper-Phenanthroline Compounds

Abstract

We examine the role of molecular symmetry and hydrogen bonding in determining heterochiral intermolecular π–π stacking motifs in four racemic compounds with the formula [Cu­(phen)2(H2O)]­[MF6]·xH2O (M = Ti, Zr, Hf; phen = 1,10-phenanthroline) and two racemic compounds with the formula Cu­(phen)2MF6·H2O (M = Zr, Hf). In this work, equimolar combinations of C 2-symmetric Δ- and Λ-Cu­(phen)2(H2O)2+ complexes were found to organize via only face-to-face π–π stacking interactions to adopt a new horizontal packing motif in a series of compounds with the formula [Cu­(phen)2(H2O)]­[MF6]·xH2O (M = Ti, Zr, Hf). Previously, Δ- and Λ-Cu­(phen)2(H2O)2+ complexes had been observed to pack with only parallel displaced π–π stacking interactions in a diagonal packing motif or with both face-to-face and parallel displaced π–π stacking interactions in a zigzag packing motif. The horizontal arrangement reported here is associated with the formation of hydrogen-bonding networks that link cations, anions, and hydrating water molecules within these structures. Equimolar combinations of neutral Δ- and Λ-Cu­(phen)2MF6 (M = Zr, Hf) molecules organize in a zigzag stacking pattern that originates from the presence of both parallel displaced and face-to-face π–π stacking interactions. The symmetry of the Cu­(phen)2MF6 molecule is reduced to C 1 by tilting of the bound MF6 2– octahedron, which renders the two phen ligands symmetrically inequivalent.

Beyond π–π Stacking: Understanding Inversion Symmetry Breaking in Crystalline Racemates

“…However, the symmetry of the Cu cations is reduced to C 1 owing to the large tilt of the apical bound water ligand. Similar symmetry reduction in five-coordinated Cu complexes were also reported in compounds with Cu­(phen) 2 (H 2 O) 2+ cations and Cu­(phen) 2 MF 6 (phen = 1,10-phenanthroline; M = Zr, Hf) molecules. , In addition, the angles between the Cu atom and centroids of the ligands are quite different between the two unique cations, with Cation 1 being 151.41° and Cation 2 being 169.82° (Figure a). Notably, the angle in Cation 2 is distinctly larger than the rest of cations in this study.…”

“…The parallel heterochiral π–π stacking interactions in compounds 1– 5 can be explained by the steric effect of the methyl groups on the ligands, in that the bulk methyl groups favors parallel stacking to minimize free volume . Similar parallel heterochiral π–π packings were observed in racemic compounds with other methyl-substituted ligands and the aromatic ligand 1,10-phenanthroline, and an inversion center is always found between the racemates. ,, As a result, although the asymmetric unit of the discussed compounds contains equivalent BBUs, the BBUs are related by different symmetry elements, resulting in different extended structures. The racemic chains display a similar pattern but have different compositions between the NCS and CS structures.…”

Crystal structures of two copper(I)–6,6′-dimethyl-2,2′-bipyridyl (dmbpy) compounds, [Cu(dmbpy)2]2[MF6]·xH2O (M = Zr, Hf; x = 1.134, 0.671)

“…The MF 6 2À anions with hydrogen-bonded water molecules are interlaced between the racemic chains to form the extended three-dimensional structure. Compared to other molecular compounds with MF 6 2À anions in an extended and complicated hydrogen network (Gautier et al, 2012;Nisbet et al, 2020Nisbet et al, , 2021, the MF 6 2À anions in (I) and (II) experience less distortion because the hydrogen-bonding contacts are less extensive and only occur along the same axis due to the site symmetry of hydrogen-bonding interactions (Kunz & Brown, 1995;Halasyamani, 2004).…”

A Tellurium-Substituted Heteropolyniobate with Unique π–π Stacking and Ionic Conduction Property

“…The centroid–centroid distances between the aromatic rings and the perpendicular distances between the phen planes are 3.599–4.008 and 3.351–3.412 Å, respectively. Such a stacking pattern suggests the existence of π–π interactions between the two phen ligands of two neighboring hybrid clusters . From the perspective of the whole structure, each cluster interacts with four neighboring ones through intermolecular π–π stacking along two perpendicular directions (Figure S7).…”

“…Such a stacking pattern suggests the existence of π−π interactions between the two phen ligands of two neighboring hybrid clusters. 34 From the perspective of the whole structure, each cluster interacts with four neighboring ones through intermolecular π−π stacking along two perpendicular directions (Figure S7). S3), which help to stabilize the hybrid cluster structure.…”