Synthesis and Studies of a Series of Linear Mixed-valence Nickel-based and Asymmetric Hetero-polynuclear Metal String Complexes
Date Issued
2012
Date
2012
Author(s)
Hua, Shao-An
Abstract
Over the past few decades, a considerable number of studies have been made on metal string complexes which are believed to have the potential to be used for future nano-electronics. In order to develop new generation of metal string complexes, two series of them, which contain a mixed-valence polynickel backbone or a heterometallic framework, have been studied.
The first study concerns two kinds of mixed-valence polynickel metal strings. The first kind is a symmetrical type nickel string, which includes [Ni7(bnapy)4Cl2](Cl)2 (3), [Ni9(bnapya)4Cl2](PF6)2 (4), [Ni7(bnapy)4Cl2](PF6)4 (5) and [Ni9(bnapya)4Cl2](PF6)4 (6) (bnapy2– = 2,6-bis(1,8-naphthyridylamido)pyridine and bnapya3– = bis(6-(1,8-naphthyridyl-
amido)pyridyl)amido). The extended nickel string complexes 3 and 4 possess two redox-active [Ni2(napy)4]3+ units. The electronic communication between the two redox-active units in both complexes can be investigated not only by magnetic measurements but also by analyzing the difference between two consecutive one-electron oxidation peaks (∆E1/2) of 3 and 4. The antiferromagnetic coupling between the two [Ni2(napy)4]3+ fragments becomes weaker as the metal frameworks elongated (J = –13.21 and –1.48 cm-1 for 3 and 4, respectively). Moreover, the ∆E1/2 values of 3 and 4 are 110 and 84 mV, respectively, which are smaller than that (300 mV) of their pentanickel analogue [Ni5(bna)4(Cl)2](PF6)2 (bna– = bisnaphthyridylamido) (1). These ∆E1/2 values indicate that the electronic communication decreases with increasing the number of inner diamagnetic nickel ions in nickel string complexes. The second type is an asymmetrical type of metal strings. The (4,0)- [Ni7(phdptrany)4Cl](PF6) (phdptrany3– = 2-(phenyldipyridyltriamido)-1,8-naphthyridine, 7) displays an intriguing electronic structure among the Ni-based metal string family. Because of the different coordination abilities on the terminal positions of phdptrany3–, complex 7 exhibits a charge disproportionate metal framework (Ni2)3+–NiII–NiII–(Ni3)7+ that contains two MV units with delocalized Ni–Ni bonds. This interesting character is first observed by analysis of Ni–Ni bond distances, which display remarkable contraction in comparison with other similar asymmetrical Ni-strings. Then, the antiferromagnetic interaction (J = –53.3 cm–1), as well as the absorption in the Near-IR region, indicative of the existence of two MV units within the metal framework. Furthermore, DFT calculations reveal that the relative lower energy of this charge disproportionational model compared to the charge localized model (0.63 eV).
In the second part, three asymmetrical heteronuclear compounds [NiRu2Ni2(tpda)4(NCS)2] (10), [Ru2Co3(tpda)4(NCS)2] (11) and [Re2Ni2(tpda)4(NCS)](PF6) (12) (tpda2–= tripyridyldiamido) are synthesized and characterized. By using techniques such as 1H NMR, IR, electrochemistry, UV/Vis/Near-IR and magnetism, the purity and the electronic structures are investigated. Complexes 10 and 11 can be regard as the extension of [RuRuM(dpa)4Cl2] type of heteronuclear metal strings. The combination of different metal ions within the metal framework provides the great potentials for the design the future electronic devices. Complex 12, on the contrary, displays an unambiguous structural character due to the asymmetrical arrangement of tpda2– ligand. It shows a very short Re–Re distance about 2.1695(4) Å. The electronic structure of 12 can be ascribed as a NiII–NiII–ReIII–ReIII chain. Interestingly, the non-coordinated pyridyl rings might be useful for the further coordination that results in the formation of MA–MA –MB–MB–MC type metal string complex.
Subjects
Metal string
Conductance
Metal wire
Nano-Wire
Inorganic compound
Type
thesis
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