The x-ray crystal structure of Na 2 [Cu(phenobarbiturate) 4 ] has been determined, in spite of the difficulties in maintaining single crystals. The complex crystallizes in space group P4/n cc witha = 16.790(7) a, b = 16.790(7) a, c = 20.56(1) a, V = 5796(6) a 3 , and Z = 4. The structure has been refined to R = 0.090. The Cu(II) ion is coordinated to four deprotonated phenobarbiturate ligands in a symmetric square planar geometry. The four Cu-N bond distances are 1.96(1) a and the N-Cu-N bond angles are exactly 90.0 o . The Na ions are surrounded by four carbonyl oxygen atoms from four phenobarbiturate ligands and four solvent water oxygen atoms in a cubic geometry. The interpretation of the spectral properties previously reported is related to the crystal structure.