Coordination Complexes Exhibiting Anion···π Interactions: Synthesis, Structure, and Theoretical Studies

The polydentate ligand 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (dpyatriz) in combination with the Cu(ClO₄)₂/CuX₂ salt mixtures (X⁻ = Cl⁻, Br⁻, or N₃⁻) leads to the formation of molecular coordination aggregates with formulas [Cu₃Cl₃(dpyatriz)₂](ClO₄)₃ (2), [Cu₃Br₃(dpyatriz)₂](ClO₄)₃ (3), and [Cu₄(N₃)₄(dpyatriz)₂(DMF)₄(ClO₄)₂](ClO₄)₂ (4). These complexes consist of two dpyatriz ligands bridged via coordination to Cu^II and disposed either face-to-face in an eclipsed manner (2 and 3) or parallel and mutually shifted in one direction. The copper ions complete their coordination positions with Cl⁻ (2), Br⁻ (3), or N₃⁻, ClO₄⁻, and N,N-dimethylformamide (DMF) (4) ligands. All complexes crystallize together with noncoordinate ClO₄⁻ groups that display anion···π interactions with the triazine rings. These interactions have been studied by means of high level ab initio calculations and the MIPp partition scheme. These calculations have proven the ClO₄⁻···[C₃N₃] interactions to be favorable and have revealed a synergistic effect from the combined occurrence of π−π stacking of triazine rings and the interaction of these moieties with perchlorate ions, as observed in the experimental systems.