The synthesis and characterization of a new constrained tetraazamacrocyclic ligand, 1,4,8,11 -tetraazabicyclo[9.3.3]-heptadecane (1, 11-C-3-cyclam), is reported. Because of its basicity, this ligand (pK(a) of the protonated form > 13.5) requires aprotic solvents for its metalation reactions. Two complexes of this ligand, [Ni(1,1 1 -C-3-cyclam](OTf)(2) and [Co(1,11-C-3-cyclam)(NCS)(2)](OTf), have been characterized by single-crystal X-ray crystallography. For the Ni(II) complex, the 1,5-diazacyclooctane (claco) subunit of the ligand is in the chair-boat conformation, whereas that same subunit in the Co(III) complex is in the chair-chair conformation. For the Ni(II) complex, C(12) and H(12a) block one of the coordination sites. The H-1 and C-13 NMR spectra of the Ni(II) complex in D2O have very sharp resonances, indicative of low-spin Ni(II). The resonance for H(12a) appears at 4.5 ppm, suggesting an interaction with Ni(II). In acetonitrile, the H-1 and C-13 spectra are broadened, indicative of a low-spin/high-spin equilibrium due to axial coordination by acetonitrile. C(12) experiences the greatest degree of broadening in the C-13 NMR spectrum. Variable-temperature NMR spectroscopy from -70 to +80 degreesC shows no significant change as a function of temperature. The electronic spectrum of the Ni(II) complex (lambda(max) = 449.9 nm) is consistent with steric and electronic factors for this complex.