Structure determination and magnetic studies of triazole chelated Co(II) coordination polymers

Abstract

AbstractTwo cobalt(II) halide complexes with 1,2,4‐triazole as a ligand were synthesized. Their structures were determined by extended x‐ray absorption fine structure (EXAFS) and powder x‐ray diffraction (XRD). Both complexes [Co(Htrz)Cl2]n (1) and {[Co(Htrz)2(trz)]BF4}n (2) form one‐dimensional polymeric chain and the distances of Co⋯Co are 3.3521(2) Å and 3.8629(2) Å, respectively. The Htrz and Cl− are bridging ligands to connect two Co(II) ions in 1, and the local environment of Co site is in a distorted octahedron with {CoN2Cl4} core. In complex 2, two Htrz and one trz are bridging ligands to connect two Co(II) ions, and the local geometry of Co is in a pseudo octahedron with {CoN6} core. The analysis of Co LII,III‐edge XAS indicates that the Co(II) of both complexes are at high spin state with t2g5eg2 configuration and the crystal field strength (10Dq) is about 1.2 eV. The broken‐symmetry DFT calculations indicate that antiferromagnetic coupling state of Co⋯Co is the most stable state in both complexes; and the coupling constants of 1 and 2 are −0.32 cm−1 and −3.70 cm−1, respectively. Based on the distances of Co⋯Co and coupling constants, such antiferromagnetic interaction is achieved through triazole ligands.