Complexation of Crown Ethers and Podands with Tropylium Cations: Determination of Stability Constants and Crystal Structure of the Dibenzo-24-Crown-8-Tropylium Cation Complex.

Molecular recognition and supramolecular chemistry in the gas phase

“…Crown ether complexes with alkali, earth alkali, and ammonium ions are not only the classics of supramolecular chemistry, but also have the advantages to be easy to generated by different ionization methods; i.e., mainly FAB and ESI, but also 252 Cf plasma desorption (Malhotra et al, 1990). Furthermore, crown ether complexes with more extraordinary cations, such as pyridinium (Lämsä et al, 1998a), tropylium (Lämsä et al, 1998b), benzenediazonium (Laali & Lattimer, 1989;Laali, 1990;Kuokkanen, 1997), transition metals (Alvarez et al, 1997), Fe(CO) n þ (Gren et al, 1995), and others (Bose et al, 1983) have been described. Also, oxygen binding to perfluorinated crown ethers was described (Brodbelt et al, 1991a,b), although it is not clear whether the O 2 À. anion radical is non-covalently bound at all.…”

Synthesis of podands bearing aromatic end groups and complex formation with tropylium tetrafluoroborate in 1,2-dichloroethane

“…Similar characteristics were also displayed by the optimized 1,7-bis(phenyl)-1,4,7-trioxaheptane-tropylium and 1,7-bis(3-methoxyphenyl)-1,4,7-trioxaheptanetropylium cation structures derived from the unsatisfactorily solved structure of the 2B18C6-tropylium tetrafluoroborate complex. 4 The observed edge-to-face interaction between the aromatic units in the calculated structures differs from the interaction in the crystal structures of the complexes formed between dibenzocrown ethers and tropylium cation, where the face-toface stacking is observed. 4 The calculated structures emphasize the importance of the interactions between oxygen atoms in the podand framework and tropylium cation.…”

“…4 The observed edge-to-face interaction between the aromatic units in the calculated structures differs from the interaction in the crystal structures of the complexes formed between dibenzocrown ethers and tropylium cation, where the face-toface stacking is observed. 4 The calculated structures emphasize the importance of the interactions between oxygen atoms in the podand framework and tropylium cation. The lower stability constant of the 1,8-diphenoxyoctane (two oxygen atoms) than P1 (four oxygen atoms) complexes in DCE solution (Table 1) agrees well with the importance of direct interactions between oxygen atoms and the tropylium ion.…”

“…18 As a starting point we took the crystal structure of the 2B24C8-tropylium tetrafluoroborate complex. 4 The cyclic structure of the crown ethers was broken by removing one of the polyether chains and the counter ion was also taken away. Figure 4 shows the geometry-optimized structure of the P1-tropylium ion complex.…”

“…2 Recently, investigations in host-guest chemistry have focused on molecular recognition and the potential of pp interactions to secure strong and selective binding for organic molecules. We have demonstrated that p-p stacking and cation-p interactions play a significant role in the host-guest complexation between benzene-substituted crown ethers and electron-deficient aromatic carbenium ions such as tropylium 3,4 and pyridinum. 5 Tropylium ion has been shown to be an ideal guest for investigation of p-p interactions.…”