Solvation of SCN^- and SeCN^- Anions in Hydrogen-Bonding Solvents

Abstract

The primary solvation sphere surrounding the thiocyanate or the selenocyanide anion in protic solvents, such as methanol, N-methylformamide and formamide, forms intimate hydrogen bonds with these anions. These interactions perturb the electron density and vibrational modes of these anions and can therefore be studied by NMR and infrared spectroscopies. In neat solutions, these solvents form hydrogen bonds to the nitrogen end along the molecular axis and nonaxially to the π cloud of the C−N bond, although a substantial proportion of the anions is not hydrogen bonded. In nitromethane solutions, the thiocyanate and selenocyanide anions form weak complexes with methanol and the amide solvents (K < 1 M-1), which is an order of magnitude smaller than that of OCN- with the same solvents, determined in our previous investigation of the cyanate anion. The remarkable differences in the solvation of these singly charged anions can be understood by theoretical calculations of their electrostatic potentials.

Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations

“…Since the linear absorption at a given frequency depends on the population and the second power of the transition dipole moment at that frequency, 11 an excess of solvent structures giving rise to red frequencies or enhanced transition dipole strength on the red side of the line relative to the blue side can generate a red wing. Simulations [41][42][43] and experiments 49,50 have found that the transition dipole of nitriles in hydrogen bonding solvents is frequency dependent, i.e., the non-Condon effect. Indeed, this is reflected in the DFT-derived data for the frequency and transition dipole derivative shown in Fig.…”

“…A comparison of the CN stretch of SeCN in the polar aprotic solvent dimethylformamide (DMF) versus the polar protic solvent formamide (FA) found an increase in the peak frequency (2066.5 cm 1 vs. 2068 cm 1 ) and linewidth (12.5 cm 1 vs. 24.0 cm 1 ), respectively. 50 This suggests that SeCN oscillators involved in stronger hydrogen bonds are shifted to the blue side. 49 This is supported by gas phase harmonic frequency calculations at the B3LYP/aug-cc-pVDZ level of a single SeCN and a SeCN • • • H 2 O complex.…”

Effects of molecular association on mutual diffusion: A study of hydrogen bonding in dilute solutions

“…Recently, there has been a considerable amount of interest in the study of the role that hydrogen bonding plays in solvation. [4][5][6][7][8][9] In previous work, 10,11 we developed a method of using diffusion measurements to determine the relative strength of hydrogen bonding and the number of solvent molecules associated with an aromatic solute containing one polar functional group in dilute solution. This method, however, is unable to provide more insights into the solute-solvent interactions.…”

Influence of Selenocyanate Ligands on the Transition Temperature and Cooperativity of bapbpy-Based Fe(II) Spin-Crossover Compounds

“…In principle, indeed, N−H···X hydrogen bonding, and thus cooperativity, should be weaker with X = Se than with X = S, as the negative charge on the selenium atom is lower than that on sulfur. 50,51 We hypothesize that structural effects might play a role in this compound: if the intermolecular N···Se and N···S distances are almost identical, the larger ionic radius of Se (184 pm) compared to S (170 pm) might increase the strength of the N−H···Se hydrogen-bonding network, leading to higher cooperativity compared to the thiocyanate case. Alternatively, other intermolecular interactions may play a role (e.g., π−π stacking), which will only be discovered by obtaining the crystal structures of both compounds.…”