Structure of the tetraphenyl borate complex of the indoloquinoline alkaloid cryptolepine

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The crystal and molecular structure of the complex, cryptolepine-tetraphenylborate, C16H13N2+·(C6H5)4B−, has been determined by direct methods. The pale yellow crystals are monoclinic, P21/n, a = 11.039(5), b = 16.4918(7), c = 16.404(2) Å, β = 95.70(1)°, V = 2968.75 Å3, and Z = 4. The structure exhibits an unusual form of static disorder with the planar cryptolepine molecules occupying a cleft between tetraphenyl borate molecules. The disorder involves essentially planar cryptolepine molecules packed in one of two orientations in the cleft, related by an almost exact noncrystallographic twofold rotation axis passing through the molecules. The tetraphenyl borate cation, on the other hand, shows no disorder. The distribution of bonds around the boron atom is essentially tetrahedral and the four phenyl rings are planar within experimental error.

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