Coordination complexes exhibiting anion-pi interactions: synthesis, structure and theoretical studies

Abstract

[eng] 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 CuII and disposed either faceto- 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.