6-Amino-1,3-dimethyl-5-[(E)-2-(methyl-sulfan-yl)benzyl-idene-amino]-pyrimidine-2,4(1H,3H)-dione-1,3,7,9-tetra-methyl-pyrimido[5,4-g]pteridine-2,4,6,8-tetrone (1/1).

In the title co-crystal, C(12)H(12)N(6)O(4)·C(14)H(16)N(4)O(2)S, both mol-ecules are essentially planar [maximum deviations = 0.129 (1) and 0.097 (1) Å, respectively]. The tricyclic and Schiff base mol-ecules are alternately stacked along the a axis and are linked by π-π inter-actions with centroid-centroid distances of 3.5170 (16) and 3.6576 (17) Å. An intra-molecular C-H⋯O hydrogen bond and a C-H⋯S contact occur in the Schiff base molecule. In the crystal, N-H⋯O, N-H⋯N and C-H⋯O hydrogen bonds lead to the formation of a three-dimensional network.