An oscillating C2(2-) unit inside a copper rectangle.
[Cu4(mu-dppm)4(mu4-eta1,eta2-C[triple bond]C-)]2+ has been shown by 31P and 1H NMR studies to undergo two fluxional processes in solution, the oscillation of the C[triple bond]C2- unit inside the copper rectangle and the flipping of the diphosphines, and this has been supported by DFT(B3LYP) calculations.
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