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 (-)(3)) leads to the formation of molecular coordination aggregates with formulas [Cu3Cl3(dpyatriz)(2)](ClO4)(3) (2), [Cu3Br3(dpyatriz)(2)](ClO4)(3) (3), and [Cu-4(N-3)(4)(dpyatriz)(2)(DMF)(4)(ClO4)(2)](ClO4)(2) (4). These complexes consist of two dpyatriz ligands bridged via coordination to Cull 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 N-3(-), ClO4-, and N,N-dimethylformamide (DMF) (4) ligands. All complexes crystallize together with noncoordinate ClO4- groups that display anion center dot center dot center dot pi 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- center dot center dot center dot [C3N3] interactions to be favorable and have revealed a synergistic effect from the combined occurrence of pi-pi stacking of triazine rings and the interaction of these moieties with perchlorate ions, as observed in the experimental systems.