A new 3D metal organic framework Ca-SBF based on a zigzag-shaped tetranuclear calcium oxocluster and 9,9'-spirobi[9H-fluorene]-2,2',7,7'-tetracar-boxylic acid was obtained and exhibited flu topology. Ca-SBF underwent a single-crystal-to-single-crystal transformation to form Ca-SBF-1 with a slight structure shrinkage. Activated Ca-SBF showed permanent porosity and CO2 adsorption properties. A Ca-SBF-modified quartz crystal microbalance sensor demonstrated selective response to toluene vapor.