Pressure-induced switching in a copper(ii) citrate dimerCCDC reference numbers 762644-762647. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c001376e

High pressure single crystal X-ray diffraction and high pressure single crystal electronic spectroscopic studies of a copper( ii ) citrate dimer are reported, allowing us to correlate the change in local structure at the Cu( ii ) centres with the observed piezochromism. A Cu( ii ) dimer displays reversible piezochromic switching due to the change in the Cu( ii ) coordination environment, specifically a pressure-induced reduction in the Cu( ii ) α-carboxylate distance.