Coordination chemistry of a fused triazolopyrazine ligand favoring structural anion···π interactions

This is the authors' abstract. We don't add key points for this paper.

The fused heterocyclic ligand 1,2,4-triazolo[4,3-a]pyrazine (L1) is a rigid heterocyclic building block capable of pyrazolate-like coordination modes while retaining neutral electronic character. Here, we examine the coordination chemistry of this species for the first time. While the ligand proved unstable under solvothermal conditions, using mild synthetic conditions we have isolated three new coordination polymers, poly-[Zn(µ2-L1)Cl2] (1), poly-[Ag2(µ3-L1)2(µ2-C3H6O)](BF4)2·C3H6O (2) and poly-[Cu2(µ3-L1)2(µ2-L1)](X-)2 (X- = NO3, 3a; PF6, 3b). Both doubly and triply bridging coordination modes are observed in these species, and close anion···π interactions with the electron deficient ligand backbone are observed in all three complexes as dominant structural features. Although N2 and CO2 adsorption experiments shows the linear solvent channels in complex 3b are not accessible to guests after evacuation, retention of crystallinity on drying and air exposure indicates robust bonding in this species comparable to related fused azolate anions.