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

We examine the role of molecular symmetry and hydrogen bonding in determining heterochiral intermolecular π-πstacking 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 C2-symmetric Δ- and λ-Cu(phen)2(H2O)2+ complexes were found to organize via only face-to-face π-πstacking 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-πstacking interactions in a diagonal packing motif or with both face-to-face and parallel displaced π-πstacking 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-πstacking interactions. The symmetry of the Cu(phen)2MF6 molecule is reduced to C1 by tilting of the bound MF62- octahedron, which renders the two phen ligands symmetrically inequivalent.