Dinuclear nickel complexes of phenol-based dinucleating macrocycles: Synthesis, structure, and properties

Hisashi Okawa, Yuichiro Aratake, Ken Ichiro Motoda, Masaaki Ohba, Hiroshi Sakiyama, Naohide Matsumoto

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Dinuclear Ni2(II,II) complexes with the formula [Ni2(Rm,n)](ClO4)2 ((m,n)= (2,2) (1), (2,3) (2), (2,4) (3)) have been obtained where (Rm,n)2- denotes the macrocycles containing two 2,6-bis(iminomethyl)-4-methylphenolate entities combined through two lateral chains, -(CH2)m- and -(CH2)n-, at the imino nitrogens. [Ni2(R2,2)](ClO4)2 (1) crystallizes in the triclinic crystal system, space group P 1̄, with Z=1, a=8.396(2) Å, b= 10.021(2) Å, c=8.104(2) Å, α=109.56(2)°, β=99.40(2)°, γ=79.89(2)°, V=628.5(3) Å3 and Z=1. The refinement converges with R=0.0384 and Rw=0.0415 for 2075 reflections with |Fo | > 3σ( |Fo |). In the centrosymmetric [Ni2(R2,2)]2+, a pair of Ni(II) ions are bridged by two phenolic oxygens with the Ni⋯Ni separation of 2.801(1) Å. Each Ni assumes a planar configuration with Ni-O bond distances of 1.842(3) and 1.838(3) Å and Ni-N bond distances of 1.814(3) and 1.823(3) Å. In the solid state, 1 is diamagnetic (S1=S2=0) whereas [Ni2(R2,3)]-(ClO4)2 (2) and [Ni2(R2,4)](ClO4)2 (3) are of a mixed-spin (S1=0, S2=1). In DMSO and pyridine all the complexes assume high-spin (S1=S2=1). The Ni2(II,II) complexes are electrochemically reduced in DMSO or pyridine to Ni2(I,II) and Ni2(I,I) complexes. The conproportionation constants of the Ni2(I,II) complexes are determined to be 3.4×104-1.2×105 in DMSO and 1.6×103-2.6×105 in pyridine. The Ni2(I,II) and Ni2(I,I) complexes of 1-3 have been prepared by electrolysis in DMSO. The mixed-valent complexes of 1 and 2 are characterized by an intervalence (IV) transition band at 790 and ∼700 nm, respectively, and belong to Class II using the classification of Robin and Day. The Ni2(I,II) complex of 3 shows no IT band (Class I). The Ni2(I,II) complexes of 1-3 show well-resolved ESR spectra due to the spin-coupled ST = 1/2 ground-state. The Ni2(I,I) complexes of 1-3 are all ESR- innocent probably due to the strong antiferromagnetic interaction.

Original languageEnglish
Pages (from-to)293-302
Number of pages10
JournalSupramolecular Chemistry
Issue number3-4
Publication statusPublished - 1996

All Science Journal Classification (ASJC) codes

  • General Chemistry


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