Cu
3(O
2C
16H
23)
6·1.2C
6H
12, containing a Cu
36+ core in an equilateral triangle geometry, has been found to be a versatile model system for investigating the spin-frustration phenomenon in a triangular lattice. It affords well-resolved EPR spectra from both of the two possible (
Stotal =
1/
2 and
3/
2) spin states of the Cu
36+ core. From 295 to 100 K, the spectra consist of a triplet, but with the central line overlapped by an additional, sharp peak, which replaces the triplet at 30 K and below. The triplet was thus assigned to the excited state with
Stotal =
3/
2, located at 324 ± 5 K (~225 cm
-1), with the zero-field parameters
D = -535 G,
E = 0,
g![](/images/entities/par.gif)
= 2.209 and
g![](/images/entities/bottom.gif)
= 2.057. The singlet was attributed to the
Stotal =
1/
2 state, with
gxx = 2.005,
gyy = 2.050,
gzz = 2.282, and, surprisingly, a hyperfine splitting arising from a single Cu
2+ nucleus, with
Azz = 157 G. The detailed magnetic measurements on a three-electron, equilateral triangular system, and the observation of symmetry lowering in the doublet ground state, should be of broad theoretical and experimental interest in molecular magnetism.