Herein we report a study on water adsorption/desorption-triggered single-crystal to single-crystal transformations in a MOF, by single-crystal and humidity-controlled powder X-ray diffraction and water-sorption measurements. We identified a gate-opening effect at a relative humidity of 85% upon water adsorption, and a gate-closure effect at a relative humidity of 55 to 77% upon water desorption. This reversible breathing effect between the >open> and the >closed> structures of the MOF involves the cleavage and formation of several coordination bonds. ; This work was supported by the Spanish MINECO through project PN MAT2015-65354-C2-1-R and by EU FP7 through ERC-Co grant agreement no. 615954. I. I. and J. A. thank the MINECO for a RyC grant (RYC-2010-06530) and a FPU predoctoral grant (AP2010-5934), respectively. J. A. also thanks the Chemistry PhD programme of the Universitat Autònoma de Barcelona. A. C. thanks MINECO and Junta de Andalucía through research projects MAT2013-41836-R and P12-FQM-1656, respectively. ICN2 acknowledges the support from the Spanish MINECO through the Severo Ochoa Centres of Excellence Programme, under Grant SEV-2013-0295. ; Peer Reviewed