New versatile ligand family, pyrazine-modulated oligo-α-pyridylamino ligands, from coordination polymer to extended metal atom chains

Abstract

Here we designed and synthesized a new ligand, di(2-pyrazyl)amine (Hdpza) (1) and studied its coordination modes and the corresponding complexes with Cu(II), Co(II), Ni(II) and Cr(II). Hdpza is an analogue of the well-studied di(2-pyridyl)amine (Hdpa) ligand, which was used to generate the first extended metal atom chain. Three types of coordination modes were found: anti–anti style which resulted in a mononuclear compound [Cu(Hdpza)₂(H₂O)₂](ClO₄)₂ (2); anti–syn which was observed in a complex for the first time and resulted in a 2-D coordination polymer [Co(µ₂-Hdpza)₂(NCS)₂] (3); and syn–syn type which was observed in extended metal atom chains [Ni₃(µ₃-dpza)₄Cl₂] (4), [Ni₃(µ₃-dpza)₄(NCS)₂] (5) and [Cr₃(µ₃-dpza)₄Cl₂] (6). Weak antiferromagnetic coupling via Hdpza was observed in 3, whereas magnetic studies on extended metal atom chains 4 and 5 revealed that the interaction parameter was more than −200 cm⁻¹. Electrochemistry showed that the extended metal atom chains 4–6 are much more stable to oxidation than the Hdpa complexes, and are able to undergo reduction.