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A series of nickel(II) complexes with polydentate aminopyridine ligands N,N,N'-tris-[2-(2'-pyridyl)ethyl]ethane-1,2-diamine (L1), N,N,N'-tris-[2-(2'-pyridyl)ethyl]-N'-methylethane-1,2-diamine (L2), and N,N'-bis-[2-(2'-pyridyl)ethyl]-N,N'-dimethylethane-1,2-diamine (L3) were synthesized and characterized by elemental analysis and spectroscopic methods. Single-crystal X-ray diffraction studies showed that the Ni(II) ions have five-coordinate square-pyramidal geometry in [NiL2](ClO(4))(2), similar to that previously found in [NiL1](ClO(4))(2) x CH(3)NO(2) (Hoskins, B. F.; Whillans, F. D.J. Chem. Soc., Dalton Trans. 1975, 657), and square-planar geometry in [NiL3](ClO(4))(2). All three nickel(II) complexes are reduced by sodium borohydride or sodium amalgam in organic solvents to nickel(I) species, which were identified by highly anisotropic EPR spectra at 100 K: g(1) = 2.239, g(2) = 2.199, and g(3) = 2.025 for [NiL1](+); g(axially) = 2.324 and g(radially) = 2.079 for [NiL2](+) and [NiL3](+). Cyclic voltammetry of the nickel(II) complexes in acetonitrile exhibited reversible reduction waves at -1.01 V for [NiL1](2+), -0.91 V for [NiL2](2+), and -0.83 V for [NiL3](2+) versus SCE, potentials which are significantly less negative than those of most previously characterized Ni(II) complexes with nitrogen-only donor atoms. Complexes [NiL1](2+) and [NiL2](2+) showed high catalytic activity in the electroreduction of 1,2-trans-dibromocyclohexane to cyclohexene.

The analytical performance of several mercury-coated iridium ultramicroelectrode arrays (IrUMEAs) was studied using square wave anodic stripping voltammetry (SWASV) for determination of cadmium in a pH 4.5 acetate buffer. The microlithographically fabricated IrUMEAs consisted of either 20 or 25 individual disk shaped UMEs, each 10 mm in diameter. The insulating layer utilized in the fabrication process was either silicon dioxide (5000 Å ) or silicon nitride (1500 Å or 2500 Å ). Calibration plots demonstrated good linearity for cadmium from 0-100 ppb. Standard deviations, detection limits, and correlation coefficients were calculated to determine the stability and reproducibility of the IrUMEAs. Repetitive cycles of depositing and stripping Hg at the IrUMEA surface resulted in increased distortion and loss of the SWASV signal. Atomic force microscopy revealed a subtle transformation in the IrUMEA surfaces.

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