The crystal structure of a new complex of a diaza-crown ether having two side arms has been determined from X-ray diffraction data. The compound crystallizes in space group P (1) over bar with cell dimensions a = 9.982(1), b = 10.685(1), c = 20.376(2)Angstrom, alpha = 81.09(1), beta = 80.92(1), gamma 88.43(1)(0), Z = 2. The structure has been solved by direct methods and refined to the final R value of 0.053 for 3458 observed reflections and 424 parameters. The diaza-18-crown-6 ligand adopts an approximate D-3d conformation. The Na+ ion is held inside the molecular cavity of this macroring ligand and a ClO4- oxygen coordinates with Na+. The average Na-O (18-crown-6) and Na-N bond lengths are 2.426(4) and 2.786(5)Angstrom, respectively; the Na-O (ClO4-) bond length is 2.472(4)Angstrom. The mean cavity radius is 1.10 Angstrom and the N ... N nonbonding distance is 4.605(6)Angstrom.