| Summary: | 博士 === 國立臺灣大學 === 化學研究所 === 96 === Over the past few decades, a considerable number of studies have been made on metal strings which are believed to have the potential to be used for future nano-electronics. In order to develop new generation of metal strings, two series of them, which contain a mixed-valence pentanickel backbone or a heterometallic framework, have been studied. The first study concerns two new linear pentanickel complexes, [Ni5(bna)4(Cl)2](PF6)2 (6) and [Ni5(bna)4(Cl)2](PF6)4 (7) (bna = binaphthyridylamide), which were synthesized and structurally characterized. The metal framework of complex 7 has a standard [Ni5]10+ core, isoelectronic and isostructural with the metal core of Ni5(tpda)4Cl2, (12) (tpda = tripyridyldiamide). The terminal nickel atoms of 7 are in high-spin state (S = 1) and antiferromagnetic coupled (J = -15.86 cm -1). Complex 6, however, displays the first characterized linear nickel framework in which the usual sequence of NiII atoms has been reduced by two electrons. Each dinickel unit attached to the naphthyridyl moieties is assumed to undergo a one-electron reduction, whereas the central nickel formally remains NiII. Magnetism, NIR spectroscopy and DFT calculation suggest that the metal framework of the mixed-valence complex 6 should be described as intermediate between a localized picture corresponding to NiII-NiI-NiII-NiI-NiII and a fully delocalized model represented as (Ni2)3+-NiII-(Ni2)3+, and is assigned to Robin-Day Class II of mixed-valence complexes. Scanning tunnelling microscopy (STM) methodology was used to assess the conductance and the resistance of single molecules of [Ni5(bna)4(NCS)2](NCS)2 (8) and Ni5(tpda)4Cl2 (11) which are the derivative of complexes 6 and 12. Compound 8 was found to be ~40% more conductive than 11. This result that could be assigned to the electron mobility induced by mixed-valency in the naphthyridyl fragments.
In the second part, two heteronuclear compounds CuPdCu(dpa)4Cl2 (9) and CuPtCu(dpa)4Cl2 (10) were obtained. They are isoelectronic to the oxidized form of the tricopper complex [Cu3(dpa)4Cl2]+ (13), previously characterized and investigated by Berry et al. The magnetic properties and the EPR spectra of 9 and 10 were reported. For 9, there is a weak antiferromagnetic interaction (J = -7.45 cm-1) between the Cu(II) magnetic centers. For 10, the antiferromagnetic interaction sharply decreased to -0.77 cm-1. These properties are at variance with those of 13, for which a relatively strong antiferromagnetic interaction (J = -34 cm-1) has been reported. DFT calculations reproduce the decrease of the magnetic interaction from 9 to 13 and assign it to the role of the nonmagnetic metal (CuIII and PdII) in the transference of the superexchange interaction.
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