Synthesis and Magneto-Structural Study of Distorted Octahedral Co^II Complexes with Picolinamide and Azide (μ_1,1)-Bridge

Two compounds [Co₂(pa)₂(μ_1,1-N₃)₂]n (1) and [Co₄(pa)₆(μ_1,1-N₃)₆] (2), (pa=picolinamide) were obtained and studied by electronic and magnetic spectroscopies. 1 is a polymer and 2 is a tetramer of mixed-valence Co^II/III. The N₃⁻ anions act as bridges between cobalt ions in the μ_1,1 coordination mode. UV-Vis spectrum analysis showed the octahedral distortion of the compounds. ESR solution spectra revealed a low-spin ground state, s=1/2 ((Formula presented.)) for Co^II. The energy gap was J> (Formula presented.) between levels, (Formula presented.) to (Formula presented.), of 2; consequently, its transition would not be observed. 1 showed zero-field splitting of the excited level (Formula presented.) with D∼0.31 cm⁻¹. Hyperfine (⁵⁹Co, I=7/2) and superhyperfine (¹⁴N, I=1) couplings were observed. Magnetic susceptibility studies (3–300 K) revealed antiferromagnetic exchange interactions in 1 and 2 with exchange coupling constants, J₁=−108 cm⁻¹ and J₂=−20 cm⁻¹, g=2 and s= (Formula presented.), for the Co(2)-Co(2) magnetic exchange pathways.