Issue 23, 1998

Structural, spectroscopic and electrochemical studies of binuclear nickel(II) complexes of bis(pentadentate) ligands derived from bis(1,4,7-triazacyclononane) macrocycles

Abstract

Binuclear nickel(II) complexes of bis(pentadentate) ligands generated by functionalisation of the four secondary nitrogens in bis(tacn) macrocycles with 2-pyridylmethyl arms have been prepared, isolated and characterised. The pentadentate compartments are linked by (CH2)2 {tmpdtne, [Ni2(tmpdtne)(OH2)2][ClO4]4·5H2O 1}, (CH2)3 {tmpdtnp, [Ni2(tmpdtnp)(OH2)2][ClO4]4 2}, (CH2)4 {tmpdtnb, [Ni2(tmpdtnb)(OH2)2][ClO4]4 3}, CH2C6H4CH2-m {tmpdtnm-X, [Ni2(tmptdtm-X)(OH2)2][ClO4]4·3H2O 4} and CH2CHOHCH2 {tmpdtnp-OH, [Ni2(tmpdtnp-OH)(OH2)2][ClO4]4 5} bridging units. Single crystal X-ray diffraction studies of 3 have confirmed that each nickel(II) centre is in a distorted octahedral geometry defined by five N-donors from a pentadentate compartment of the ligand and an oxygen donor from a water ligand. Tetragonal elongation of the geometry is evidenced by the axial Ni–N distances, which are ca. 0.05 Å longer than the three equatorial Ni–N distances. The two pentadentate compartments are oriented in an anti configuration with the two aqua ligands pointing away from each other. Cyclic and square-wave voltammetric studies on 1–5 indicate that the complexes undergo oxidation to the nickel(III) state in two overlapping 1e processes (i.e. NiIINIII → NiIINiIII → NiIIINiIII). Two partially resolved 1e oxidation waves were observed for 1 and 5 while for 2–4 two 1e processes were indicated by fact that the signals were broader than expected for a single 2e process.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1998, 3919-3926

Structural, spectroscopic and electrochemical studies of binuclear nickel(II) complexes of bis(pentadentate) ligands derived from bis(1,4,7-triazacyclononane) macrocycles

S. J. Brudenell, L. Spiccia, A. M. Bond, P. C. Mahon and D. C. R. Hockless, J. Chem. Soc., Dalton Trans., 1998, 3919 DOI: 10.1039/A806084C

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