Density functional calculations reveal a flexible version of the copper paddlewheel unit: implications for metal organic frameworks.

Density functional theory calculations on [Cu2(O2CR)4L2] systems reveal a change in ground state with increasing Cu-L bond strength. For L = N-heterocyclic carbene (NHC), the Jahn-Teller axis switches from parallel to orthogonal to the Cu-Cu vector and the copper coordination geometry becomes highly flexible. While the calculated dimer/monomer equilibrium for isolated complexes slightly favours monomers, the preformed paddlewheel units embedded in many metal organic frameworks are potential targets for developing novel materials.