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

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)(H(2)O)(2)](ClO(4))(2) (2); anti-syn which was observed in a complex for the first time and resulted in a 2-D coordination polymer [Co(mu(2)-Hdpza)(2)(NCS)(2)] (3); and syn-syn type which was observed in extended metal atom chains [Ni(3)(mu(3)-dpza)(4)Cl(2)] (4), [Ni(3)(mu(3)-dpza)(4)(NCS)(2)] (5) and [Cr(3)(mu(3)-dpza)(4)Cl(2)] (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.