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Understanding the Role Structural Changes Play in the Formation of Strong and Weak Hydrogen Bonds in Tetramethylalkyldiammonium Dithiocyanate Salts

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journal contribution
posted on 07.01.2009, 00:00 by David J. Wolstenholme, Jan J. Weigand, Elinor M. Cameron, T. Stanley Cameron
Structural analyses for a series of tetramethylalkyldiammonium dithiocyanate salts have been carried out on low-temperature and high-resolution X-ray diffraction data. This series of organic salts contains both strong and weak hydrogen bonds which vary depending on the number of methylene groups bridging the two ammonium portions of the molecules. The S−N···H angles associated with the strong N−H···N hydrogen bonds in this series progressively decrease as the length of the alkyl bridge increases (ethylene > propylene > butylene). This results in less linear interaction between the N−H donor groups and the lone pair of the N acceptor atoms. The N,N,N′,N′-tetramethylpropylenediammonium and N,N,N′,N′-tetramethylbutylenediammonium dithiocyanate salts also produce weak C−H···N hydrogen bonds. The C−H···N and N−H···N interactions in this series undergo bifurcation, while one set of C−H···N and N−H···N hydrogen bonds in the propylene salt appears to experience a cooperative effect. A comparison of the topological properties of the electron density has shown a number of similarities and differences in the electronic nature of the strong and weak interactions in all three salts. This has all led to a better understanding of the electronic nature of these interactions and how they logically distribute themselves in the crystalline state.