HgCl 2 (Caf): Co‐crystallization of Mercuric Chloride and Caffeine

Colourless single crystals of the co‐crystallizate of mercuric chloride and caffeine, HgCl 2 (Caf), were obtained from an ethanolic solution of mercuric chloride, HgCl 2 , and caffeine (Caf) and recrystallized from hot water. The crystal structure (monoclinic, P2 1 , Z = 2, a = 398.36(8), b = 1964.5(4), c = 809.6(2) pm, β = 99.24(3)°, Z = 2, R 1 = 0.0584 for 1430 F o > 4σ(F o )) contains helical chains (parallel to the 2 1 screw axis) of almost unaffected HgCl 2 molecules and caffeine molecules which are very weakly bound to one keto‐oxygen atom (O4) of one and N9 of a second caffeine molecule at distances of 282 and 281 pm, respectively. To the contrary, theoretical calculations show that the molecule HgCl 2 (Caf) 2 is stable (in the gas phase at T = 0 K) with surprisingly strong bonding as indicated by the “tetrahedrization” of the molecule.