Novel multi-spin-state linear hexanickel complexes Ni6 11 + and their singly oxidized products Ni6 12 + with 1,8-naphthyridine-based ligands: Tuning the redox properties of the metal string
Journal
Polyhedron
Journal Volume
26
Journal Issue
14
Pages
3833-3841
Date Issued
2007
Author(s)
Abstract
The new ligand, 2,7-bis(α-pyrimidylamino)-1,8-naphthyridine (H2bpmany), was prepared by the reaction of 2,7-dichloro-1,8-naphthyridine with 2-aminopyrimidine in the presence of sodium tert-butoxide under palladium-catalyzed conditions. The linear hexanickel Ni611 + complexes [Ni6(μ6-bpmany)4X2]Cl (X = Cl (1); X = NCS (2)) and their singly oxidized products [Ni6(μ6-bpmany)4X2](BF4)2 (X = Cl (3); X = NCS (4)) have been synthesized, and compounds 1, 2 and 4 have been crystallographically characterized. The crystal structures of the Ni611 + complexes show remarkably short Ni-Ni distances (ca. 2.22 Å), clearly indicative of partial metal-metal bonding in the mixed-valence Ni23 + unit. This is also verified by the axial X-band EPR spectra of the complexes in solution. Magnetic susceptibility measurements reveal that the Ni611 + complexes exhibit antiferromagnetic interactions (J = -47 cm-1) between the terminal Ni2+ ion and the central Ni23 + unit, and the Ni612 + complexes exhibit weak antiferromagnetic interactions (J = -5 cm-1) between the two terminal Ni2+ ions. The cyclic voltammograms display three reversible redox waves at E(1)1/2 = +0.87, E(2)1/2 = -0.02 and E(3)1/2 = -0.46 V for 1, and E(1)1/2 = +0.96, E(2)1/2 = -0.01, and E(3)1/2 = -0.41 V for 2. The relatively low potentials of E(2)1/2 suggest that the Ni611 + complexes can be easily converted to their Ni612 + forms. © 2007 Elsevier Ltd. All rights reserved.
Type
journal article