I am interested in the nature of the chemical bonds between the copper(II) ions in the structure of HKUST-1 (CuBTC, Cu3BTC2, MOF-199). I have already found, that in the paddle-wheel structure of copper(II)-carboxylate complexes superexchange (antiferromagnetic coupling) occurs between the two copper(II) ions through the carboxylate groups (if I understood well). The structure of the HKUST-1 is built up from similar paddle-wheel units, and I have read in several articles that copper(II) dimer presents in the structure. Could Somebody please explain me what does it exactly mean?

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