The nano-scale molecule with the longest delocalized metal–metal bonds: linear heptacobalt(<scp>ii</scp>) metal string complexes [Co₇(µ₇-L)₄X₂]

Abstract

A new type of pyrazine-modulated oligo-alpha-pyridylamino ligands, N2-(pyrazin-2-yl)-N6-(6-(pyrazin-2-ylamino)pyridin-2-yl)pyridine-2,6-diamine (H3pzpz) and N2-(pyrazin-2-yl)-N6-(6-(pyridin-2-ylamino)pyridin-2-yl)pyridine-2,6-diamine (H3tpz), were synthesized and characterized by IR, 1H NMR and MS(FAB). Using and , the linear heptacobalt(II) metal string complexes [Co7(micro7-L)4X2] (L=pzpz3-, X=Cl-, NCS-; L=tpz3-, X=Cl-, X=NCS-) were synthesized and structurally characterized. The structures showed the shortest Co-Co distance (2.194 A) and the longest Co chain (13.5 A) obtained to date with direct Co-Co bonds. The Co-Co distances are in the range 2.194-2.309 A. Electrochemical studies showed two reversible oxidations and one reversible reduction, while all the redox reactions of H3pzpz complexes, and , occurred at higher potentials than H3tpz complexes, and . The complexes are fairly stable to oxidation. Temperature-dependent magnetic research on revealed anomalous magnetic behavior with intermediate magnetic moment values between quartet and doublet states, and deviation from the Curie-Weiss law.