A seven-coordinate dimmer has been synthesized with 5-oxo-4-oxa-tricyclo[4. 2.1.0]nonane-9-carboxylic acid and 1,10-phenanthroline. The crystal structure was determined by single-crystal X-ray structural analysis. The crystal belongs to a monoclinic system, space group P2 1ln, with α=1.552 08(12) nm, b = 1.065 52(8) nm, c=1.626 57 (12) nm, β=100.100 (10)°, V=2.648 3 (3) nm 3, D c= 1.643 gcm- 3, Z=2, F (000)= 1 328, Final GooF=1.026, R l= 0.026 2, wR 2=0.059 2. The crystal structure shows that the cadmium ion is coordinated with five oxygen a...