Article: Studies from Q.H. Huang and co-authors have provided new information about crystallography.

"Reaction of 2-(methylsulfanyl) pyrimidin-4-amine with the 5-(methoxyvinylidene) derivative of Meldrum's acid and subsequent heating of the product in Dowtherm fluid yielded the title compound, C8H7N3OS, which was proven to contain a bicyclic 4H-pyrimido[1,6-a] pyrimidine system," investigators in the United States report.

"All non-H atoms of the molecule are coplanar within 0.15 angstrom. The bond-length distribution in the bicyclic core shows localization of the double bonds," wrote Q.H. Huang and colleagues.

The researchers concluded: "The geometry of the intramolecular S center dot center dot center dot O 1,5-contact [2.534 (2) angstrom] is ...

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