title: Asymmetric tetranuclear nickel chains with unidirectionally ordered 2-(α-(5-phenyl)pyridylamino)-1,8-naphthyridine ligands.
abstract: The new ligand, 2-(α-(5-phenyl)pyridylamino)-1,8-naphthyridine (Hphpyany), was synthesised by a palladium(0)-catalysed reaction of 2-chloro-1,8-naphthyridine with 2-amino-5-phenylpyridine in the presence of potassium tert-butoxide. Linear tetranickel metal complexes, [Ni4(phpyany)4Cl2](CF3SO3) 1, [Ni4(phpyany)4Cl2](BF4)22, [Ni4(phpyany)4(NCS)2](ClO4) 3 and [Ni4(phpyany)4(NCS)2](CF3SO3)24 were prepared and crystallographically characterised. Complexes 1-4 demonstrate that, for the first time, four asymmetric ligands align unidirectionally and thus configure (4,0)-form tetranickel strings, specifically, with the phenyl groups of the four phpyany-pointing to one side of the Ni4chain and naphthyridyl to the other. The remarkably short Ni-Ni distances (ca. 2.33 Å) for 1 and 3 indicate partial metal-metal bonding, which can be viewed as both complexes containing one mixed-valence Ni23+unit. The measurements of the magnetic susceptibility reveal that Ni47+complexes 1 and 3 exhibit antiferromagnetic interactions (J = -42 cm-1for 1 and -46 cm-1for 3) between the terminal Ni2+ion and the Ni23+unit, while Ni48+complexes 2 and 4 exhibit antiferromagnetic interactions (J = -33 cm-1for 2 and -35 cm-1for 4) between the two terminal Ni2+ions. The results of the cyclic voltammetry indicate the presence of two reversible redox couples at E1/2(1)= 0.12 V, E1/2(2)= -0.65 V for 1, and at E1/2(1)= 0.12 V, E1/2(2)= -0.72 V for 3. The products of the first oxidation for 1 and 3 are the oxidised species 2 and 4, respectively. The values of single-molecule resistance (15.4 (±3.46) MΩ for 3 and 16.2 (±5.04) MΩ for 4) were determined by STM-based break-junction methods. The results represent the first conductance measurements of linear tetranickel chains.
authors.affiliation: Department of Chemistry and Center for Emerging Material and Advanced Device National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, Taiwan, R.O.C. smpeng@ntu.edu.tw.
authors.forename: Lien-Hung
authors.initials: LH
authors.lastname: Tsou
authors.affiliation: Institute of Chemistry, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, Taiwan, R.O.C.
authors.forename: Marc
authors.initials: M
authors.lastname: Sigrist
authors.affiliation: Institute of Chemistry, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, Taiwan, R.O.C.
authors.forename: Ming-Hsi
authors.initials: MH
authors.lastname: Chiang
authors.affiliation: Department of Chemistry and Center for Emerging Material and Advanced Device National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, Taiwan, R.O.C. smpeng@ntu.edu.tw.
authors.forename: Er-Chien
authors.initials: EC
authors.lastname: Horng
authors.affiliation: Department of Chemistry and Center for Emerging Material and Advanced Device National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, Taiwan, R.O.C. smpeng@ntu.edu.tw.
authors.forename: Chun-Hsien
authors.initials: CH
authors.lastname: Chen
authors.affiliation: Department of Chemistry and Center for Emerging Material and Advanced Device National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, Taiwan, R.O.C. smpeng@ntu.edu.tw.
authors.forename: Shou-Ling
authors.initials: SL
authors.lastname: Huang
authors.affiliation: Department of Chemistry and Center for Emerging Material and Advanced Device National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, Taiwan, R.O.C. smpeng@ntu.edu.tw.
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Center for Emerging Material and Advanced Device National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, Taiwan, R.O.C. smpeng@ntu.edu.tw and Institute of Chemistry, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, Taiwan, R.O.C.
authors.forename: Shie-Ming
authors.initials: SM
authors.lastname: Peng