H2S Complexes Research Articles

Mixed H2S and H2O Clusters─New Insights into Dispersion-Dominated Hydrogen Bonding.

Here, we report the results of an IR spectroscopy study on heteroclusters of H2S and H2O and several of their isotopomers using mass-selective IR spectroscopy in superfluid helium nanodroplets in the range of 2560-2800 cm-1. Based on DFT calculations on the B3LYP-D3/6-311++G(d,p) level of theory, we were able to assign the experimentally observed O-D stretching bands to heterodimer and heterotrimer clusters. Since no bands of the S-H-bound conformer HSH···OH2 could be observed, we were able to determine the O-H-bound conformer HOH···SH2 to be the global minimum structure. A trapping of the local minima in helium nanodroplets was not observed. This is in line with the weaker hydrogen bond expected for H2S complexes. In these clusters, the interaction energy is expected to be more dominated by dispersion and less dictated by highly directional electrostatic forces.

Assessing the pollution level of a subtropical lake by using a novel hydrogen sulfide fluorescence technology

Hydrogen sulfide (H2S) is an important environmental toxin with bi-directional biological effects on organisms. In natural waters, H2S complexes with heavy metal ions in an anaerobic environment influence heavy metals' bioavailability and induce phosphorus release and eutrophication in water columns. Traditional detection techniques, such as colorimetric, electrochemical, and chromatographic, cannot simultaneously detect H2S and pollution assessment of subtropical lakes. To address these technical defects, we developed small-molecule fluorescent probes to evaluate the pollution level in natural water bodies. This method relies on the combination of the probes’ response signals to raw water and the water quality index, thereby enhancing the accuracy and reliability of water quality assessments. Furthermore, this novel material has a large Stokes shift. It can detect complex levels of H2S concentrations in natural water bodies by correlating the degree of contamination and fluorescence signals. The development of this visual research tool for detecting environmental H2S levels in natural water bodies is expected to have meaningful, practical applications.

Structures and Energetics of Elemental Sulfur in Hydrogen Sulfide

Severe safety concerns arise from sulfur deposition that occurs frequently in the development of high sulfur-content natural gas formation. Solubility reduction of elemental sulfur in H2S is the main reason of sulfur deposition. To understand how elemental sulfur, which exists in the form of sulfur clusters (Sn), interacts with H2S, quantum chemistry calculations are performed to study the structures and thermodynamic properties of Sn–H2S complexes. Weak interaction resulting mainly from intermolecular sulfur–sulfur interaction is revealed for these complexes. The complexes formed by S4, S6 and S8 have similar binding energies that are relatively higher than that of S2–H2S. Because of their small binding energies and Gibbs free energies, these complexes may coexist in formation, but are however easily decomposed or formed depending on stratigraphic or pipeline conditions. Our calculations reveal the status of elemental sulfur in H2S, which is useful for subsequent predictions on sulfur solubility and sulfur deposition in high sulfur-content natural gas formation.

The nature of the Sulfur-Metallic bonds (Metal = Ni, Pd and Pt) in doped gold nanoclusters: A density functional approach

“Atomically precise gold nanoparticles” that constitute single guest atom doped gold cores besides being protected by ligands, have drawn much attention in the fields of biology, chemistry and physics. To investigate the foundation of organic-metallic interface, metallic alloy- H2S complexes are used to model the core-ligand interactions. In this work, simulation of platinum group doped gold dimers and triangular trimers bonded to H2S, are investigated. To simulate experimental results, features including bond lengths, vibrational frequencies and binding energies were calculated for the dimers of platinum group metals and gold, via DFT. The Au-M dimers have minimum magnetic dipole moments compared to the dimers of two platinum group metals. Among the three platinum group atoms simulated, the relativistic effect prevents Pd from being tightly bonded to other metallic atoms. The “donor-acceptor” model is put forward for the complexes of H2S molecules and dimer/trimers, to explain the interaction of sulfur-metal bonds. The possibility of neighboring metallic atoms affecting the acceptor, Au or platinum group metallic atoms is distinct. A neighboring acceptor may improve the S-M interaction such as S-Ni bond while a neighboring weak donor may reduce the S-M interactions such as S-Pd/Pt bonds. With the isosurface plot of densities of electrons/holes at binding, one can identify that such an interaction involves both electrostatic and covalent features. The complexes having H2S as ligand and cores of the real gold clusters verified the reliability of the donor-acceptor model qualitatively.

Raman spectroscopic study of polysulfanes (H2Sn) in natural fluid inclusions

Sulfur-bearing methane inclusions with up to 68 mol% H2S in metamorphic quartzite from Bastar Craton (India) exhibit common ν1 vibration modes of H2S and CH4 at 2609 cm−1 and 2919 cm−1, respectively, associated with unknown Raman bands at 2488, 2503, 2574, and 2899 cm−1. The fluid inclusions generate molecular hydrogen and surplus sulfur during irradiation with a 532 nm, 25 mW laser, thus indicating photolytic breakdown of polysulfanes – H2Sn. Quantum chemistry modeling based on the density functional theory was conducted to better understand the origin of the unusual Raman bands in the SH-stretching region. Vibrations of simple H2S, H2S2, H2S3, H2S4, H2S5, S6–8 molecules were simulated together with selected complexes of n = 1–4 polysulfanes with the crown-shaped, orthorhombic cycloocta-sulfur identified in the fluid inclusions according to intense Raman bands at 60–62, 79–80, 149–151, 218–220, 441–442, and 472–474 cm−1. Theoretical calculations confirmed that the vibrations at 2488, 2503, and 2574 cm−1 reflect symmetric and asymmetric, H-bonded and non-H-bonded H2S2…S8…H2S2, H2S2…S8 and H2S…S8…H2S complexes in the crystallized sulfur melt. A small band at 2899 cm−1 is tentatively attributed to CH3–S8– and/or –CH2–S8– bonds, which also diminished during irradiation with green laser. “Phantom” bands occasionally occurring at >2580 cm−1 were identified as artificial bands, resulting from an imprecise angle of incidence of laser beam to rotatable holographic grating. Another small 2579 ± 1 cm−1 band in Raman spectra recorded using longer acquisition times represents a combination band of host quartz, rather than the A12ν4 resonant vibration of CH4 located at the same frequency.

Acid-Base Formalism Extended to Excited State for O-H···S Hydrogen Bonding Interaction.

Hydrogen bond can be regarded as an interaction between a base and a proton covalently bound to another base. In this context the strength of hydrogen bond scales with the proton affinity of the acceptor base and the pKa of the donor, i.e., it follows the acid-base formalism. This has been amply demonstrated in conventional hydrogen bonds. Is this also true for the unconventional hydrogen bonds involving lesser electronegative elements such as sulfur atom? In our previous work, we had established that the strength of O-H···S hydrogen bonding (HB) interaction scales with the proton affinity (PA) of the acceptor. In this work, we have investigated the other counterpart, i.e., the H-bonding interaction between the photoacids with different pKa values with a common base such as the H2O and H2S. The 1:1 complexes of five para substituted phenols p-aminophenol, p-cresol, p-fluorophenol, p-chlorophenol, and p-cyanophenol with H2O and H2S were investigated experimentally and computationally. The investigations were also extended to the excited states. The experimental observations of the spectral shifts in the O-H stretching frequency and the S1-S0 band origins were correlated with the pKa of the donors. Ab initio calculations at the MP2 and various dispersion corrected density functional levels of theory were performed to compute the dissociation energy (D0) of the complexes. The quantum theory of atoms in molecules (QTAIM), noncovalent interaction (NCI) method, natural bonding orbital (NBO) analysis, and natural decomposition analysis (NEDA) were carried out for further characterization of HB interaction. The O-H stretching frequency red shifts and the dissociation energies were found to be lower for the O-H···S hydrogen bonded systems compared to those for the O-H···O H-bound systems. Despite being dominated by the dispersion interaction the O-H···S interaction in the H2S complexes also conformed to the acid-base formalism, i.e., the D0 and the O-H red shift scaled with the pKa of the donor, similar to that observed in the O-H···O interaction. However, the two classes of H-bonds follow different correlations. In addition we also discuss the nuances associated with the similarity and differences in the hydrogen bonding properties of the two classes in the ground electronic state as well as in the excited state.

Dissociation Energies of Sulfur-Centered Hydrogen-Bonded Complexes.

In this work we have determined dissociation energies of O-H···S hydrogen bond in the H2S complexes of various phenol derivatives using 2-color-2-photon photofragmentation spectroscopy in combination with zero kinetic energy photoelectron (ZEKE-PE) spectroscopy. This is the first report of direct determination of dissociation energy of O-H···S hydrogen bond. The ZEKE-PE spectra of the complexes revealed a long progression in the intermolecular stretching mode with significant anharmonicity. Using the anharmonicity information and experimentally determined dissociation energy, we also validated Birge-Sponer (B-S) extrapolation method, which is an approximate method to estimate dissociation energy. Experimentally determined dissociation energies were compared with a variety of ab initio calculations. One of the important findings is that ωB97X-D functional, which is a dispersion corrected DFT functional, was able to predict the dissociation energies in both the cationic as well as the ground electronic state very well for almost every case.

Structural, energetic and vibrational properties of some van der Waals complexes of CO2, OCS and OCSe

As part of a study of the properties of some chalcogen-bonded complexes with NH3, H2O, PH3 and H2S, we have investigated the oxygen-bound species containing CO2, OCS and OCSe by means of molecular orbital calculations at the ab initio level. The structures of the NH3, H2O and PH3 complexes are all similar, with a primary C…X interaction (X = N, O, P) and one of the hydrogen atoms approaching an oxygen atom in a weak secondary attraction. The H2S complexes show a greater variety of alternative structures. The changes in the monomer geometrical parameters, the interaction energies and the harmonic vibrational spectra vary in general in a systematic way as the acid and the base are changed. Deviations from this systematic behaviour have been rationalised.

The hydrogen bond: a molecular beam microwave spectroscopist’s view with a universal appeal

In this manuscript, we propose a criterion for a weakly bound complex formed in a supersonic beam to be characterized as a 'hydrogen bonded complex'. For a 'hydrogen bonded complex', the zero point energy along any large amplitude vibrational coordinate that destroys the orientational preference for the hydrogen bond should be significantly below the barrier along that coordinate so that there is at least one bound level. These are vibrational modes that do not lead to the breakdown of the complex as a whole. If the zero point level is higher than the barrier, the 'hydrogen bond' would not be able to stabilize the orientation which favors it and it is no longer sensible to characterize a complex as hydrogen bonded. Four complexes, Ar2-H2O, Ar2-H2S, C2H4-H2O and C2H4-H2S, were chosen for investigations. Zero point energies and barriers for large amplitude motions were calculated at a reasonable level of calculation, MP2(full)/aug-cc-pVTZ, for all these complexes. Atoms in molecules (AIM) theoretical analyses of these complexes were carried out as well. All these complexes would be considered hydrogen bonded according to the AIM theoretical criteria suggested by Koch and Popelier for C-H...O hydrogen bonds (U. Koch and P. L. A. Popelier, J. Phys. Chem., 1995, 99, 9747), which has been widely and, at times, incorrectly used for all types of contacts involving H. It is shown that, according to the criterion proposed here, the Ar2-H2O/H2S complexes are not hydrogen bonded even at zero kelvin and C2H4-H2O/H2S complexes are. This analysis can naturally be extended to all temperatures. It can explain the recent experimental observations on crystal structures of H2S at various conditions and the crossed beam scattering studies on rare gases with H2O and H2S.

Estimates of the second dissociation constant of H2S from the surface sulfidation of crystalline sulfur

The adsorption of hydrogen sulfide (ΓH2S) and protons (ΓH+) on the surface of crystalline sulfur was investigated experimentally in H2S-bearing solutions at temperatures of 25, 50, and 70°C, NaCl concentrations of 0.1 and 0.5 mol/dm−3 and log CH+ values in the range −2.3 to −5. At all temperatures, the dominant process on the surface of the sulfur was deprotonation, and the average values of ΓH2S were very close to the highest values determined for ΓH+. This finding, combined with the lack of detectable proton adsorption in H2S-free solutions, suggests that proton adsorption/desorption on the surface of sulfur occurs through formation of S − H2S complexes in the presence of H2S.We propose that this complexation represents sulfidation of the sulfur surface, a process analogous to hydroxylation of oxide surfaces, and that the sulfidation can be described by the reaction: S + H2S = SSH20 β° The deprotonation of the SH° complex occurs via the reaction: SSH20 = SSH− + H+ β− Values of 2.9, 2.8, and 2.9 (± 0.23) were obtained for −log β− at 25, 50, and 70°C, respectively. These data were employed to estimate the second dissociation constant for hydrogen sulfide in aqueous solutions using the extrapolation method proposed by Schoonen and Barnes (1988) and yielded corresponding values for the constant of 17.4 ± 0.3, 15.7, and 14.5, respectively. The value for 25°C is in very good agreement with the experimentally determined values of Giggenbach (1971) at 17 ± 0.1; Meyer et al. (1983) at 17 ± 1; Licht and Manassen (1987) at 17.6 ± 0.3; and Licht et al. (1990) at 17.1 ± 0.3.

On the efficient generation of Arn–SH free-radical clusters via ultraviolet photolysis of closed-shell Arn–H2S complexes

Detailed investigations are described for the generation of open-shell radical complexes formed by unimolecular photolysis of closed-shell van der Waals precursors. As a specific test case, ultraviolet photolysis of slit-jet cooled Arn–H2S (n⩽2) complexes at both 248 and 193 nm are shown to yield Ar–SH and Ar2–SH radical cluster species with surprisingly high efficiencies. Analysis of the laser induced fluorescence (LIF) spectra indicates that the radical complexes are produced with extensive van der Waals stretch/bend and overall rotational excitation, which is consistent with a simple ballistic model of the dissociation dynamics. The LIF spectra obtained as a function of expansion distance downstream provide clear evidence for remarkably efficient cooling of the newly formed radical cluster species by low-energy collisions with jet-cooled inert gas atoms at ≈10 K. Spectrally resolved Ar–SH and Ar2–SH LIF signals have been investigated as a function of Ar composition, which yields information on relative branching ratios for fragmentary (e.g., Ar2–H2S→Ar–SH+H+Ar) and nonfragmentary (e.g., Ar2–H2S→Ar2–SH+H) photolysis events.

Extension of the Karplus relationship to vicinal coupling within the P–Ru–S–H moiety of the H2S complexes cis-RuX2(P–N)(PPh3)(SH2) {X = Cl, Br; P–N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine}

The Ru(II)–H2S complexes cis-RuX2(P–N)(PPh3)(SH2) {X = Cl, Br; P–N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine} are characterised crystallographically and by 31P{1H}, 1H and 1H{31P} NMR spectroscopies; the 1H NMR spectra at –50 °C show three-bond coupling of only one H-atom of the coordinated H2S to the P-atom of the P–N ligand, and this represents an extension of the Karplus relationship to vicinal coupling within a P–Ru–S–H system.

Ab initio molecular orbital calculations on hydrogen- and non-hydrogen-bonded complexes. H2CO·H2O and H2CO·H2S

Different complexes between H2CO and H2O and H2CO and H2S have been investigated using large basis set SCF calculations. It is found that in both cases a hydrogen-bonded complex is the most stable. Estimates of the dispersion contribution to the binding energies have been made. It is found that the dispersion interaction is of the same order of magnitude as the SCF-binding energy for the H2CO·H2S complexes. The results are discussed in comparison with matrix infrared spectroscopic data.