Abstract
5,7,9‐Trimethyl3~3~cyclophane (1), with two binding sites of different donating ability, adopts a C~3~ conformation both in the solid state (−170 °C) and in CD~2~Cl~2~ solution at −90 °C. 5,7,9‐Trimethyl3~3~cyclophane‐2,11,20‐trione (9) has the same C~3~ symmetry, while 3~3~cyclophane‐2,11,20‐trione (12) adopts the C~s~ structure in the solid state (−170 °C). The structures of 1 and 9 are the first examples of C~3~ or C~3h~ symmetries in the 3~3~cyclophanes; their preferred conformers are C~s~ both in solution and in the solid state. The cyclophane 1 shows much stronger donating ability than the parent 3~3~cyclophane (2). In the TCNQ‐F~4~ (1:1) complex of 1, the donor (D) and the acceptor (A) are stacked alternately, with partial and complete D‐A overlaps being observed in the solid state (−170 °C) in the forms of partial D‐A overlap of the methyl‐substituted benzene face and TCNQ‐F~4~ and of nearly complete D‐A overlap of the methyl‐unsubstituted benzene face and TCNQ‐F~4~. The former type of overlap is generally observed in the TCNQ‐F~4~ complexes of the [3~n~]cyclophanes, and the transannular D‐A distance (3.22 Å) is much shorter than that in the latter (3.58 Å). This supports the idea that the methyl‐substituted benzene ring interacts more strongly than the methyl‐unsubstituted benzene ring with the acceptor. Consistently with this, two types of acceptor columns are observed, and the transannular distances between acceptors are 3.45 Å for the methyl‐unsubstituted side and 3.26 Å for the methyl‐substituted side. In the 2,11,20‐trithia3~3~cyclophane (4)‐TCNQ‐F~4~ (1:1) complex, an alternating D‐A stacking similar to that in 3~3~cyclophane (2)‐TCNQ‐F~4~ (1:1) is observed. The acceptors are stacked in a parallel fashion and form an infinite column, the A−A distance in the (4)‐TCNQ‐F~4~ (1:1) complex being 3.10 Å, and the acceptors in the unit cell are arranged parallel in a plane, the A‐A distance being 3.12 Å. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)