Single crystal EPR studies of the Cu2Cl84− ions in the complex tris(ethylenediamine)cobalt(III) di-μ-chloro-bis[trichlorocuprate(II)] dichloride dihydrate

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Abstract
Single crystal electron paramagnetic resonance studies have been carried out on the exchange‐coupled pairs of copper(II) ions contained in the title compound. EPR measurements were made at X‐, K‐, and Q‐band microwave frequencies at selected temperatures in the range 2–77 °K. The angular variation of the Q‐band spectra taken at 4.2 and 77 °K were used to diagnonalize the appropriate spin Hamiltonian. The Zeeman interaction and the zero‐field interactions were found to have different principal coordinate systems. Although the dipolar interaction dominates the zero field splitting, a small but finite contribution from the anisotropic exchange interaction is present. The temperature dependence of the spectrum indicates that an interdimer exchange interaction is also present. The interdimer interaction causes the fine structure of the triplet excitations to be averaged into a single resonance line at 77 °K. The temperature of coalescence of the fine structure is 17 °K. Although the fine structure is resolved at liquid helium temperatures, owing to the lower density of excitations, the hyperfine interaction is averaged out by motion of the excitations produced by the effective interdimer exchange. The spin Hamiltonian parameters of the isolated excitations and the interdimer exchange frequency have been determined. These results are discussed in terms of the crystal and molecular structure of the complex.