Structure of the tetraphenyl borate complex of the indoloquinoline alkaloid cryptolepine

The crystal and molecular structure of the complex, cryptolepine-tetrapheny lborate, C16H13 N-2(+).(C6H5)(4)B-, has been determined by direct methods. The pale yellow crystals are monoclinic, P2(1)/n, a = 11.039(5), b = 16.491 8(7), c = 16.404(2) Angstrom, beta = 95.70(1)degrees, V = 2968.75 Angstrom( 3), and Z = 4. The structure exhibits an unusual form of static disorder wi th the planar cryptolepine molecules occupying a cleft between tetraphenyl berate molecules. The disorder involves essentially planar cryptolepine mol ecules packed in one of two orientations in the cleft, related by an almost exact noncrystallographic twofold rotation axis passing through the molecu les. The tetraphenyl berate cation, on the other hand, shows no disorder. T he distribution of bonds around the boron atom is essentially tetrahedral a nd the four phenyl rings are planar within experimental error.