Organic ammonium halides as analogues of main-group amide/imide complexes in the solid state: Extension of ring-laddering and ring-stacking principles
✍ Scribed by Andrew D. Bond
- Publisher
- Elsevier Science
- Year
- 2005
- Tongue
- English
- Weight
- 1000 KB
- Volume
- 249
- Category
- Article
- ISSN
- 0010-8545
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✦ Synopsis
The structural chemistry of primary, secondary and tertiary ammonium halides is reviewed with emphasis on application of ring-laddering and ring-stacking concepts in the organic solid state. Similarities between motifs observed in the crystal structures of the ammonium halides and in amide/imide complexes of main-group elements suggest a general analogy between R x NH 4-x + X -(X = Cl, Br, I) and R x N (3-x)-M (3-x)+ (M = principally Group 1/Group 2 cations and derivatives of Group 13 elements, e.g. [AlR] 2+ , [AlR 2 ] + , [GaR] 2+ , [GaR 2 ] + , etc.). The origin of the analogy lies in comparable directional preferences for association of the cations and anions in both the organic and main-group systems. Although similar motifs are observed amongst the organic and main-group structures, directly comparable ammonium and amide/imide moieties (i.e. R x NH 4-x + and R x N (3-x)-with identical R groups) rarely form comparable motifs. This is attributed primarily to different metric features: N + (-H)• • •X -distances in the organic sample are significantly longer than N• • •M distances in the main-group complexes. This affects the balance between electrostatic forces that promote further association of the cationic and anionic moieties and the (principally steric)