Synthesis and Molecular Structures of Nickel(II) Alkyl-Substituted Cyclam Complexes

Kazuya Kobiro*, Atsuyoshi Nakayama, Toshitaka Hiro, Mitsuhito Suwa, Yoshito Tobe

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


Sterically congested cyclam derivatives 2, 3s, 3a, 4, 5c, and 5t and their Ni(II) complexes have been synthesized. Magnetic susceptibility measurements of the complexes in the solid state and in water solution indicate that the less congested complexes Ni(l)2+and Ni(5t)2+are high-spin species in the solid state and Ni(l)2+, Ni(5c)2+, and Ni(5t)2+are mixtures of high-spin species and low-spin species in solution. On the other hand, highly congested complexes Ni(2)2+, Ni(3s)2+, and Ni(4)2+are shown to be low-spin species in both the solid state and in solution. Ni(3a)2+has been shown to be a high-spin species in the solid state, while it is a low-spin species in solution. Electronic spectra of Ni(l)2+, Ni(2)2+, Ni(3s)2+, Ni(3a)2+, Ni(4)2+, Ni(5c)2+, and Ni(5t)2+measured in H2O and in 5 M NaCLO4solution supported the above observations. Half-wave potentials for the NiII/NiIIIredox change (£1/2(NiII, III)) were determined for Ni(l)X2, Ni(2)X2, Ni(3s)X2, Ni(3a)X2, Ni(4)X2, Ni(5c)X2, and Ni(5t)X2(X = N03, C1O4, CI). It appeared that Ni(II) complexes with sterically congested ligands (Ni(2)2+, Ni(3s)2+, Ni(3a)2+, Ni(4)2+) show higher half-wave potentials than those of the complexes with less congested ligands (Ni(l)2+, Ni(5t)2+, Ni(5c)2+). Molecular structures of Ni(2)(NO3)2, Ni(3s)(NO3)2, Ni(3a)(NO3)2, Ni(4)(NO3)2-H2O, and Ni(5t)(NO3)2were determined by X-ray crystal structure analyses, and the steric effects of the peripheral substituents on the coordination are discussed. In Ni(5t)(NO3)2, two axial nitrate anions coordinate to the central Ni atom to give six-coordinate octahedral geometry, while in Ni(4)(NO3)2-H2O one axial nitrate anion semicoordinates to the central Ni atom to give five-coordinate square pyramidal geometry. Two types of unique structures exist in a unit cell of Ni(2)(N03)2. One of the structures A has four-coordinate square planar geometry, while in the other structure B one axial nitrate anion semicoordinates to the central Ni atom to give a five-coordinate square pyramidal geometry around the Ni atom. Ni(3a)(NO3)2possesses six-coordinate octahedral geometry, while Ni(3s)(NO3)2has four-coordinate square planar geometry with trans-I geometry of the cyclam ring.

Original languageEnglish
Pages (from-to)676-685
Number of pages10
JournalInorganic Chemistry
Issue number4
StatePublished - 1 Feb 1992

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