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EPR probing of bonding and spin localization of the doublet-quartet states in a spin-frustrated equilateral triangular lattice: Cu-3(O2C16H23)(6)center dot 1.2C(6)H(12)

We present high-frequency (34 and 95 GHz) EPR spectroscopic measurements of the magnetic parameters of both the ground state (spin-doublet) and the excited state (spin-quartet) of the model frustrated-spin triangular lattice of Cu-3(O2C16H23)(6)(.)1.2 C6H12 containing the Cu-3(6+) core. From 295 down to about 100 K, the EPR spectra from single crystals consist of a well-resolved triplet, but with the central component being overlapped by a single peak. At 4 K, the triplet is replaced by a singlet. The triplet is shown to arise from the quartet state, located at 324 K above the ground state. Its magnetic parameters are: D = -535 G, E = 0, g(u) = 2.209, g(perpendicular to) = 2.057 with the parallel direction being the three-fold axis of the CU36+ core. The singlet is assigned to the S = 1/2 ground state, with g(xx) = 2.005, g(yy) = 2.050, and g(zz) = 2.282. Its hyperfine structure was that from a single Cu nucleus, with A(zz) = 157 G, and A(xx) = A(yy) < 60 G, demonstrating that in the doublet state the unpaired electron is localized on only one of the three Cu2+ ions. We ascribe this localization to an antiferromagnetic exchange interaction between Cu-3(6+) cores, with zJ' = -0.15 K. These results serve as a basis for detailed theoretical calculations of spin dynamics and electronic bonding in a frustrated triangular magnetic lattice.

Pyrococcus-furiosus ferredoxin; Single-molecule magnets; Manganese carboxylate; Magnetization; Clusters; Crystal; Relaxation; Nanomagnet; Behavior; Complex

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