Syntheses and Studies of the Novel Linear Nona-nickel nd an Unusual Asymmetric, Mixed-Valence epta-nickel Metal String Complexes
Date Issued
2008
Date
2008
Author(s)
Hua, Shao-An
Abstract
Two kinds of ligands with a terminal naphthyridyl group, a symmetrical bis(6-(1,8-naphthyridyl-α-amino)pyridyl)amine (H3bnapya) and an unsymmetrical 2-(phenyldipyridyltriamino)-1,8-naphthyridine (H3phdptany) which were prepared and characterized by 1H-NMR and ESI-MS. First, H3bnapya ligand were applied to synthesize linear nona-nickel metal string complexes [Ni9(bnapya)4Cl2](PF6)4 (1) and its two electrons reduced form [Ni9(bnapya)4Cl2](PF6)2 (2), both were structurally characterized. As far as the electronic structure is concerned, complex 1 exhibits [Ni9]18+ metal core. The complex exhibits a weak antiferromagnet-c interaction (J = －1.51 cm-1) between the two terminal NiII ions, which have square-pyramidal coordination environment with high spin states. The magnetic coupling is significantly weak because the long distance of the two magnetic centers. Complex 1 undergoes a two-electrons reduction process leading to complex 2. Each dinickel unit attached to the naphthyridyl moieties is assumed to undergo a one-electron reduction, whereas the inner nickel ions formally remain NiII. Also, complex 2 shows an weak antiferromagnetic interaction between two (Ni2)3+ fragments, with J = －0.52 cm-1. Secondly, the unsymmetrical ligand H3phdptany were used synthesize linear hepta-nickel metal string complexes [Ni7(phdptany) 4Cl](PF6) (3), and its one-electron oxidation product [Ni7(phdptany)4Cl](PF6)2 (4). From the structural analysis, both complexes 3 and 4 are (4,0)-form because of the steric effect of the bulky phenyl groups. Magnetism, NIR spectroscopy and DFT calculations suggest that the metal framework of complex 3 should be described as a mixed-valence system of NiI, NiII and NiIII . The redox disproportionation was observed in the unsymmetrical ligand environment. The naphthyridyl site is in favor of [Ni2]3+ unit, and the amido site is in favor of NiIII .The one-electron oxidation of complex 3 occurs at naphthyridyl moiety, leading to the formation of complex 4, which are confirmed by magnetic measurement and EPR spectrum. Finally, the H3phdptany and H3bnapya ligands react with different metal precursors in MeOH leading to some mononuclear or dinuclear metal complexes 5~8. In the H3bnapya ligand system, different metals show different coordination modes.
Subjects
metal string
metal-metal bonding
mixed-valence complex
Type
thesis
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