| Abstract
| - Ureas characteristically form one-dimensional hydrogen-bonded α-networks with a repeat distanceof about 4.60 Å. Oxamides form similar α-networks with a longer 5.05 Å repeat distance. The urea of glycineand the oxamide of glycine were each cocrystallized with a series of four bipyridines, including two ureaderivatives and two oxamide derivatives. This series of eight cocrystals was studied by X-ray diffraction inorder to see what would happen when molecules that would normally form α-networks with incommensuratedistances were forced into the same crystal. The two all-urea crystals and the two all-oxamide crystals containedthe expected α-networks with repeat distances in accordance with normal urea or oxamide values. Four of thecrystals were mixed, containing both oxamide and urea molecules. Three consisted of two-dimensionalβ-networks with alternating parallel urea and oxamide subnetworks. The repeat distances averaged 4.87 Å, avalue close to the value expected for oxamides, but shorter than any previously observed examples. In thefourth mixed crystal, the urea α-network formed with a normal urea repeat distance, but the oxamide networkdid not form, the oxamide adopting an unusual molecular conformation that maximizes intramolecular hydrogenbonds instead.
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