Copper(II) complexes of 3-amino-1,2,4-triazine and 2-aminopyrazine: Strategies for designing crystalline materials using coordination polymers

Reaction of 3-amino-1,2,4-triazine (3-atz) or 2-aminopyrazine (2-apz) with Cu(hfac)2·xH2O led to the formation of the monometallic and trimetallic complexes Cu(hfac)2(3-atz)2 (1), Cu3(hfac)6(3-atz)2 (2), Cu(hfac)2(2-apz)2 (3) and Cu3(hfac)6(2-apz)2 (4). The azine molecules behave as both monodentate and bridging bidentate ligands. The Cu(II) ions exhibit a range of coordination geometries. In 1 and 3, the complex is distorted octahedral with the Jahn–Teller axis lying along one of the O–Cu–O axes. In 2 and 4, the central Cu(II) ion is also distorted octahedral with the Jahn–Teller axis lying along the N–Cu–N axis, while the terminal Cu(II) ions are five-coordinate. Structure analysis reveals that addition of the amino-substituent makes the ligands more coordinating, leading to shorter Cusingle bondN bonds. In the case of 4, this results in a stronger magnetic superexchange pathway and the complex exhibits antiferromagnetic behavior at low temperatures.