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Abstract Insights into structure‐conductivity mechanisms are investigated for a series of six (dinitrile)2LiPF6 molecular crystals with varied alkyl chain lengths, N≡C─(CH2)n─C≡N, n = 2, 3, 4, 5, 6, and 2Me‐glutaronitrile. The molecular crystals have separate Li+ and channels, with the Li+ions weakly coordinated by four ─C≡N groups. The following correlations are observed: i) shorter Li+⋯ Li+ hopping distances (5.72–8.08 Å) increase ionic conductivity (3.1 × 10−4–0.15 × 10−4 S cm−1 at 25 °C) for all (dinitrile)2LiPF6; ii) when there are unrestricted anion channels, the lithium ion transference number increases ( = 0.39–0.62) as the void volume (565–250 Å3) and Li+⋯ Li+ hopping distance (7.15–5.72 Å) decrease, since a greater fraction of the charge is contributed by the Li+ions; this correlates with n= 2, 4, 5, 6; iii) the exceptions are Gln (n = 3) and 2Me‐Gln, where there are restricted channels for anion migration, and in this case: iv) conductivity decreases (0.57–0.15 × 10−4 S cm−1 at 25 °C), since contributions to the conductivity from anion migration decrease, but v) increases (0.64–0.7) since a greater fraction of the charge is carried by the Li+ ions.
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Gated, Selective Anion Exchange in Functionalized Self‐Assembled Cage Complexes
Abstract Appending functional groups to the exterior of Zn4L4self‐assembled cages allows gated control of anion binding. While the unfunctionalized cages contain aryl groups in the ligand that can freely rotate, attaching inert functional groups creates a “doorstop”, preventing rotation and slowing the guest exchange rate, even though the interiors of the host cavities are identically structured. The effects on anion exchange are subtle and depend on multiple factors, including anion size, the nature of the leaving anion, and the electron‐withdrawing ability and steric bulk of the pendant groups. Multiple exchange mechanisms occur, and the nature of the external groups controls associative and dissociative exchange processes: these bulky groups affect both anion egress and ingress, introducing an extra layer of selectivity to the exchange. Small changes can have large effects: affinities for anions as similar as PF6−and SbF6−can vary by as much as 400‐fold between identically sized cavities.
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- Award ID(s):
- 2002619
- PAR ID:
- 10398160
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 29
- Issue:
- 11
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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