Vibrational Spectra, Crystal Structures, Constitutional and Rotational Isomerism of FC(O)SCN and FC(O)NCS

Abstract

Fluorocarbonyl thio- and isothiocyanate, FC(O)SCN and FC(O)NCS, were fully characterized by IR (gas, Ar and N(2) matrixes), Raman (liquid and solid), UV (gas), and (13)C NMR (liquid) spectroscopy, as well as single-crystal X-ray diffraction. Their vibrational and conformational properties were analyzed using matrix isolation techniques guided by quantum chemical calculation at the ab initio [MP2 and CCSD(T)], density functional theory B3LYP, and CBS-QB3 levels of theory. A complete assignment of the fundamental modes of FC(O)SCN was performed. In both the gas and liquid states, FC(O)SCN and FC(O)NCS were found to exist as two conformers (C(s) symmetry), in which the carbonyl double bond (C═O) adopts a synperiplanar (syn) and an antiperiplanar (anti) orientation with respect to either the SCN or NCS group. For FC(O)SCN, the conformational enthalpy difference, ΔH° = H°(anti) - H°(syn), was determined by matrix IR experiments to be 0.9 ± 0.2 kcal mol(-1). The conformational equilibria were evaluated by fast-cooling gaseous samples highly diluted in argon at different temperatures as cryogenic matrixes. The conformational properties of both molecules were analyzed in terms of the hyperconjugative electronic effect applying the natural bond orbital method. The kinetics of the thermal conversion of the high-energy anti into the syn FC(O)NCS conformer was studied in Ar and N(2) matrixes at cryogenic temperatures. The reversed syn → anti photoisomerization was observed using UV-vis light. Rearrangement of FC(O)SCN into FC(O)NCS was observed in the neat liquid and in solution. Under 193 nm (ArF excimer laser) irradiation, FC(O)NCS isolated in cryogenic Ar matrixes forms FC(O)SCN. At low temperature, single crystals of the two constitutional isomers were obtained using a miniature zone melting procedure. According to X-ray diffraction, they exclusively crystallize in their syn forms (C(s) symmetry) in the orthorhombic crystal system.

σ-Hole interactions in small-molecule compounds containing divalent sulfur groups R 1—S—R 2

“…They found that S atoms of the methionine residues exhibit a directed SÁ Á ÁO intramolecular interaction with an average distance of 3.6 Å . Ramos et al (2010) reported that the SCNÁ Á ÁSCN ( = 3.156 Å ) and C OÁ Á ÁSCN ( = 3.165 Å ) interactions in AMOREA stabilize its molecular layers.…”

“…All calculations were performed on the model systems using F 2 S, Cl 2 S and Br 2 S as donors of -hole and NH 3 , HCN and (CH 3 ) 2 O as acceptors of -hole, as well as the following molecules derived from CSD entries and highlighted in Fig. 1: (FOC,CN)S (from CSD entry AMOREA; Ramos et al, 2010), (CH 3 O) 2 S (from CSD entry KUYRIF; Buschmann et al, 1992), (Cl,(CH 3 ) 2 N)S (from CSD entry VAMPEF; Mitzel, 2003), methionine (from CSD entry FITLID; Dalhus & Gö rbitz, 1999) and (CN) 2 S (from CSD entry GOJZUC; Ilyukhin et al, 2014). The r S +r O (3.32 Å ), r S +r N (3.35 Å ), r S +r Cl (3.55 Å ) and r S +r S (3.60 Å ) sums of van der Waals radii were used to calculate Á using, respectively, the van der Waals radii values of 1.80 Å , 1.52 Å , 1.55 Å and 1.75 Å for the S, O, N and Cl atoms (Bondi, 1964).…”

“…3 feature electropositive areas (seen in dark blue colour) on the outer sides of the S atoms, with the most positive electrostatic potential (V S,max ) located along the extensions of their covalent bonds. This should allow nucleophiles approaching the S atom to form nearly linear -hole interactions (Rosenfield et al, 1977;Pal & Chakrabarti, 2001;Ramos et al, 2010;.…”

Chalcogen Bonds in Small-Organic Molecule Compounds Derived from the Cambridge Structural Database (CSD)

“…There are numerous computational studies reporting on interactions of divalent chalcogen atoms (acting as σ-hole bond donors), mostly in small-inorganic molecule compounds (Pal, D. & Chakrabarti, P., 2001 [1]; Politzer, P. et al, 2007 [2]; Bleiholder, C. et al, 2006 [3]; Clark, T. et al, 2007 [4]; Ramos, L. A. et al, 2010 [5]; Politzer, P. et al, 2010 [6]; Politzer, P. et al, 2013 [7]; Politzer, P. & Murray, J. S., 2013 [8]; Politzer, P. et al, 2014 [9]; Pandiyan, B. V. et al, 2016 [10]; Zabardasti, A. et al, 2017 [11]; Bauza, A. & Frontera A., 2018 [12]; 2019 [13]; 2020 [14]).…”

Preparation and Spectroscopic Studies of FC(O)SSCl

“…In particular, our research group has prepared different molecular species through the reaction of XC(O)S–Cl (X = halogen). FC(O)SNSO, ClC(O)SNSO, FC(O)SNCO, FC(O)SN, FC(O)SCN, ClC(O)SCN, FC(O)SSCN, FC(O)OSO 2 CF 3 , ClC(O)OSO 2 CF 3 and FC(O)SSC(O)F are examples of molecules synthesized either from FC(O)SCl or ClC(O)SCl.…”