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New K, Ca, and Sr complexes with diphenyloxo-18-crown-6 (2,3,5,6-dibenzo-1,4,7,10,13,16-hexaoxocyclooctadecadiene-2,5, DPO18C6) were prepared and isolated as solids. Their IR spectra (400–4000 cm−1) were studied. On the basis of spectroscopic data, a structure was proposed for these compounds. In the complexes, DPO18C6 occurs in the inner sphere of K, Ca, and Sr. Only five oxygen atoms of the crown ether are involved in coordination, and the macrocycle conformation does not depend on the nature of the metal.