The progression of strong and weak hydrogen bonds in a series of ethylenediammonium dithiocyanate derivatives—a new bonding protocol for macromolecules?

Abstract

The experimental charge densities for a series of sym-N-methyl-substituted ethylenediammonium dithiocyanate salts have been investigated based on low-temperature and high-resolution X-ray diffraction data. This series of organic dications provides both strong and weak hydrogen bonding networks that vary depending on the N-H : SCN(-) (donor/acceptor) ratios. The number of N-HN hydrogen bonds connected to each cation increases (linear to bifurcated) as the number of N-H donor groups increases. The bifurcated thiocyanate anions also form a less energetic N-HS hydrogen bond. The presence of more than one hydrogen bond acceptor on each thiocyanate anion results in a competition between the sulfur and nitrogen atoms in forming both strong and weak hydrogen bonds. The formation of a significant number of weak hydrogen bonds is shown to play a crucial role in stabilizing these organic ionic crystals. The progression of these organic dications (smaller to larger N-H : SCN(-) ratios) results in the weaker hydrogen bonds playing a smaller role in stabilizing the crystalline structures. In addition, the electron density along the saddle point has been shown to vary significantly from weak hydrogen bonds to van der Waals interactions. This has led to a better understanding of the progression of hydrogen bonding in the crystalline states of sym-N-methyl substituted ethylenediammonium dithiocyanate salts and provides insight into the relationship between strong and weak hydrogen bonds in organic ionic crystals.

Hierarchical Photothermal Fabrics with Low Evaporation Enthalpy as Heliotropic Evaporators for Efficient, Continuous, Salt-Free Desalination

“…At the interface of the CuS nanosheets, S atoms are exposed on the ridges and Cu atoms are embedded in the grooves (Figure b). The exposed S atoms have much weaker hydrogen bonding with H 2 O molecules, compared with that between O atoms and H 2 O molecules. − As a result, the PAN@CuS fabric shows a lower water-evaporation enthalpy (Figure b). In addition, the sunflower-inspired hierarchical PAN@CuS fabric is further equipped in a heliotropic evaporation model.…”

Synthesis and Structural Characterization of N,N´- Dipropyl-N,N,N´,N´-tetramethyl-1,2- ethylenediammonium Dichloride and Dibromide

“…2(b). It is interesting to note that the thiocyanate anion in {Me 3 N(CH 2 ) 2 NMe 3 }(SCN) 2 behaves the same way by showing close contacts between the nitrogen atom of the thiocyanate and the methyl hydrogens on one hand, and also between the sulfur atom and methylene hydrogens on the other hand [18].…”

“…Structural information on hexaalkyl-1,2-ethylenediammonium salts containing simple anions such as halides or pseudohalides is rather sparse comprising {Me 2 BuN(CH 2 ) 2 NMe 2 Bu}Br 2 · 2H 2 O [14], {Me 3 N(CH 2 ) 2 NMe 3 }I 2 [15], {Me 2 [Et(CH 2 ) n ]-N(CH 2 ) 2 NMe 2 [(CH 2 ) n Et]}X 2 (X = Br, n = 10 [16]; X = I, n = 10, 14 [17]), and {Me 3 N(CH 2 ) 2 NMe 3 }-(SCN) 2 [18]. In some of these crystals, hydrogen bonding networks lead to the formation of extended supramolecular structures.…”

The CH‥O H-Bond as a Determining Factor in Molecular Structure

“…Despite the generic weakness of CH as a proton donor, computations have shown that it is strong enough to engage F as an acceptor [79,103,[124][125][126][127][128][129][130][131]. Other proton-accepting atoms are S [100, [132][133][134][135][136], even as strong as 7 kcal/mol [137,138], Cl [139][140][141][142] or I [143]. Even an atom as weakly basic as P [144,145] can serve this function as can carbenes [146].…”