Study on a pyrazine-modulated tetrapyridyltriamide and its complexes: Synthesis, structure and properties

A pyrazine-modulated oligo-α-pyridylamine ligand H3pzpz and its mononuclear copper(II) and cobalt(II) complexes have been synthesized and structurally characterized. The protonated ligand cation 1 exhibits an anti-anti-anti-anti-syn-anti conformation. H3pzpz can be a quadridentate ligand and coordinates to metal atoms with all-anti mode in both copper and cobalt mononuclear complexes. The copper(II) ion in 2 is five-coordinated in tetragonal pyramid geometry with one of the perchlorate anions being weakly coordinated in the apex position. The cobalt(II) ion in 3 and 4 is six-coordinated in octahedron geometry. Extensive hydrogen bonds are formed, and construct the complexes 1 and 2 into 2D networks and 3 and 4 into 3D networks. X-band EPR spectra of 2 showed well-resolved hyperfine structures resulting from the two paramagnetic isotopes 63Cu and 65Cu, yielding g = 2.16 and A0 = 67 × 10−4 cm−1. Complexes 3 and 4 showed spin–orbital coupling and zero-field splitting that is reflected in the magnetic properties.