Molecular gears: Structures of (9,10-triptyceno) crown ethers

The incorporation of 9,10-triptycene unit in a crown ether is examined from a structural perspective. Insertion of a triptycene group into 18-crown-6 stretches the crown into an ellipse, as seen in structures presented here of 9,10-triptyceno-22-crown-6 and its thallium complex. Symmetric addition of two triptycene groups into 18-crown-6 results in the sterically congested bis(9,10-triptyceno)-26-crown-6, whose crown cavity is filled with the -clouds of two arene groups. The larger bis(9,10-triptyceno)-32-crown-8 is more sterically relaxed. The structures of these bis(triptyceno)crown ether molecules are the first with two triptycene groups simultaneously linked through their 9 and 10 positions, thereby forming a simple molecular gearing mechanism. The compound 9,10-triptyceno-22-crown-6 (1) crystallizes in the orthorhombic space group Pbca with a = 10.7962(7), b = 15.826(3), c = 31.147(5) Å, V = 5321.8(12) ų, and Z = 8; its complex with TlNO₃ (Tl-1) crystallizes in the monoclinic space group P2₁/c with a = 8.1884(14), b = 19.552(2), c = 20.575(4) Å, = 97.062(8)°, V = 3269.2(9) ų, and Z = 4; bis(9,10-triptyceno)-26-crown-6 (2) crystallizes in the triclinic space group P with a = 8.6488(11), b = 10.7718(12), c = 12.3324(12) Å, = 111.58(1), = 100.55(1), = 106.43(1)°, V = 970.3(5) ų, and Z = 1; and bis(9,10-triptyceno)-32-crown-8 (3) crystallizes in the orthorhombic space group Pna2₁ with a = 20.186(3), b = 8.558(2), c = 25.623(2) Å, V = 4426.2(14) ų, and Z = 4.