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.

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Through a new pyrazine-modulated penta-pyridyl-tetraamine ligand, H(4)N(9)-mpz, linear nonachromium(II) complexes with four quadruple metal-metal bonds were successfully obtained, and their structure, magnetic and electrochemistry properties were studied.

Pentacobalt EMACs [Co(5)(mu(5)-dpzpda)(4)X(2)] (X = Cl(-) (), NCS(-) ()) with fine-tuning of the supporting ligand based on the tripyridyldiamine ligand, N,N'-di(pyrazin-2-yl)pyridine-2,6-diamine (H(2)dpzpda), and their reduced form (Ph(4)P)[Co(5)(mu(5)-dpzpda)(4)X(2)] (X = Cl(-) (), NCS(-) ()) were first synthesized and structurally characterized. The structures of showed direct Co-Co bonds with Co-Co distances in the range 2.2385(7)-2.2888(15) A, and valence electrons delocalized through the whole metal chain with distances of longer than 9.06 A. The distances of the inner Co-Co bonds and the Co-axial ligands became longer after reduction, whereas no significant change was observed in the distances of the outer Co-Co bonds and Co-N (supporting ligand) bonds, which was consistent with the MO analysis. Electrochemical studies on both and showed one reversible oxidation and one reversible reduction at E(1/2) = +0.82 and -0.05 V for , and at E(1/2) = +0.89 and +0.02 V for , respectively. The redox reactions of the thiocyanate complex happened at higher potentials than the chloride complex . A magnetism study of revealed anomalous magnetic behaviour similar to that of heptacobalt EMACs, and a deviation from the Curie-Weiss law was observed. The chi(M)T value at 300 K is 0.84 and 1.16 emu K mol(-1) for and , respectively, suggesting spin-equilibrium or a spin-admixture between doublet and quartet states arising from the Boltzmann distribution over different energy levels. Similar results were obtained for and , showing intermediate chi(M)T values between a diamagnetic and a triplet state of 0.15-0.96 emu K mol(-1) in the temperature range 5-300 K. The structural and magnetic results were interpreted through an EHMO study.

The synthesis, crystal structures, and magnetic properties of linear tetranickel string complexes supported by mixed 2‐(α‐pyridylamino)‐1,8‐naphthyridine (Hpyany) and N‐(p‐tolylsulfonyl)dipyridyldiamine (H2tsdpda) ligands are reported. In comparing the crystal structure of [Ni4(pyany)2(tsdpda)2Cl] (1) with that of [Ni4(pyany)2(tsdpda)2Cl(H2O)](PF6) (2), the one‐electron‐reduced compound 1 displays shorter Ni(3)–Ni(4) (ca. 2.28 Å) and longer Ni(3)–N (ca. 2.02 Å) bond lengths. Similar trends have also been observed for axial NCS–‐substituted derivatives [Ni4(pyany)2(tsdpda)2(NCS)] (3) and [Ni4(pyany)2(tsdpda)2(NCS)2] (4). These structural variations indicate the formation of a mixed‐valence [Ni2]3+ unit and a three‐electron, two‐center Ni(4)–Ni(3) σ bond. Magnetic measurements of 2 and 4 show that both terminal Ni(1) and Ni(4) ions are in the high‐spin states (S = 1) and are antiferromagnetically coupled. The one‐electron‐reduced complexes 1 and 3, however, exhibit a delocalized mixed‐valence [Ni2]3+ unit (S = 3/2), which is antiferromagnetically coupled with the terminal high‐spin NiII ion.