Ab Initio Investigation of Tetrel Bonds in Isolated Complexes Formed Between a Lewis Acid H3MX, M-O or M-S (M = Si, Ge, or Sn) and the Lewis Bases B = N2, CO, HCCH, PH3, C2H4, HCN, CS, HNC, NP, H2O, and NH3.

Isolated complexes of the type B⋯A in which the noncovalent interaction is a tetrel bond have been characterized by ab initio calculations at the CCSD(T)(F12c)/cc-pVDZ-F12 level. The Lewis bases B involved were N2, CO, HCCH, PH3, C2H4, HCN, CS, HNC, NP, H2O and NH3. Two types of Lewis acid A were examined, each containing one of the tetrel atoms M = Si, Ge or Sn, The Lewis acids in the first series were the H3MX (X = F, Cl, CN, H), in each of which the most electrophilic region was found to lie on the C3 axis of the C3v molecules, near to the tetrel atom M. In the second series the Lewis acids were M-O and M-S. Graphs, consisting of calculated equilibrium dissociation energies De of each B⋯H3MX complex plotted against the nucleophilicities NB of the Lewis bases B, were used to obtain the electrophilicity EH3MX of each molecule H3MX (M = Si, Ge, Sn). The molecular electrostatic surface of potentials of the molecules M-S and M-O (M = Si, Ge, Sn) revealed that many of the B⋯M-S and B⋯M-O complexes should have a tetrel bond to M in which the axis of the M-S or M-O subunit should be approximately perpendicular to the axis of the nonbonding or π-bonding electron pair carried by B, a novel type of tetrel bond confirmed by geometry optimizations of the complexes.

Monohydrides of the Group 13 Elements M=B, Al and Ga: Axial Bi-Nucleophilicity and the Propensity to Form Both H-M⋠⋠⋠HX and M-H⋠⋠⋠HX Hydrogen Bonds (X=F, Cl, Br, I, CN, CCH, CP).

Equilibrium dissociation energies De of the hydrogen-bonded complexes HAl⋅⋅⋅HX and HGa⋅⋅⋅HX (X=F, Cl, Br, I, CN, CCH, and CP) were calculated ab initio at the CCSD(T)-(F12c)/cc-pVDZ-F12 level of theory. The gradients of graphs of De versus the electrophilicity EHX of the Lewis acids HX yielded the nucleophilicities NM-X of the Group 13 atoms M in these diatomic molecules. Molecular electrostatic surfaces potentials reveal that H-Al and H-Ga are bi-nucleophilic and that the H ends of these H-M molecules are more nucleophilic than the M ends for M=Al and Ga, but not when M=boron. Therefore, the complexes M-H⋅⋅⋅HX were investigated using the same approach. It was concluded for M=Al and Ga that, for a given X, the M-H⋅⋅⋅HX complexes were more strongly bound than the corresponding H-M⋅⋅⋅HX complexes for both M=Al and Ga but the reverse order applies for M = boron. The effects of substituting the H atoms in the M-H molecules by F atoms and by methyl groups were investigated to measure the -I and +I inductive effects relative to H, respectively, on the nucleophilicities of the molecules M-H when M is acting as hydrogen-bond acceptor in complexes H-M⋅⋅⋅H-X.

Radial Potential Energy Functions of Linear Halogen-Bonded Complexes YX···ClF (YX = FB, OC, SC, N2) and the Effects of Substituting X by Second-Row Analogues: Mulliken Inner and Outer Complexes.

Energies of linear, halogen-bonded complexes in the isoelectronic series YX···ClF (YX = FB, OC, or N2) are calculated at several levels of theory as a function of the intermolecular distance r(X···Cl) to yield radial potential energy functions. When YX = OC, a secondary minimum is observed corresponding to lengthened and shortened distances r(ClF) and r(CCl), respectively, relative to the primary minimum, suggesting a significant contribution from the Mulliken inner complex structure [O═C-Cl]+···F-. A conventional weak, halogen-bond complex OC···ClF occurs at the primary minimum. For YX = FB, the primary minimum corresponds to the inner complex [F═B-Cl]+···F-, while the outer complex FB···ClF is at the secondary minimum. The effects on the potential energy function of systematic substitution of Y and X by second-row congeners and of reversing the order of X and Y are also investigated. Symmetry-adapted perturbation theory and natural population analyses are applied to further understand the nature of the various halogen-bond interactions.

An Assessment of Radial Potential Functions for the Halogen Bond: Pseudo-Diatomic Models for Axially Symmetric Complexes B⋠⋠⋠ClF (B=N2 , CO, PH3 , HCN, and NH3 ).

The radial potential energy is calculated ab initio at the explicitly correlated level of theory CCSD(T)(F12c)/cc-pVTZ-F12 for the five axially symmetric, halogen-bonded complexes B⋅⋅⋅ClF (B=N2 , CO, PH3 , HCN, and NH3 ) as a function of the intermolecular distance r. The PE curves are fitted by the Hulburt-Hirschfelder analytical function under the assumption of a pseudo-diatomic model. The spectroscopic constants ω σ and ω σ x σ , and α σ of the intermolecular stretching mode υ σ are calculated by two closely related approaches. The first involves derivatives of a polynomial fitted to the ab initio calculated points near to re and evaluated at r=re . The second uses the constants of the fitted H-H function. Both procedures are tested on 35 ClF by fitting (a) its RKR-type function and (b) the CCSD(T)(F12c)/cc-pVTZ-F12 version. The complexes OC⋅⋅⋅ClF and H3 P⋅⋅⋅ClF behave differently from the other three. A point of inflection/secondary minimum with a shortened r(C⋅⋅⋅Cl) and an increased r(Cl-F) detected for B=CO, suggests a second isomer with a significant contribution from the valence-bond structure OC+ Cl⋅⋅⋅F- . The shape of the ab initio calculated function for H3 P⋅⋅⋅ClF is different from those involving B=N2 , HCN, or NH3 , a difference attributed to H3 PCl+ ⋅⋅⋅F- character. The ab initio generated curve for H3 P⋅⋅⋅ClF is, nevertheless, satisfactorily fitted by the three-parameter H-H function.

A test of ab initio-generated, radial intermolecular potential energy functions for five axially-symmetric, hydrogen-bonded complexes BHF, where B = N2, CO, PH3, HCN and NH3.

The radial potential energy functions for five axially symmetric, hydrogen-bonded complexes BHF (B = N2, CO, PH3, HCN and NH3) have been calculated ab initio at the explicitly correlated level of theory CCSD(T)(F12c)/cc-pVTZ-F12 as a function of the hydrogen-bond distance r(ZH), where Z is the hydrogen-bond acceptor atom of B. The remaining geometric parameters were optimised at each point in the calculation. The functions so generated were then used to estimate the spectroscopic constants ωσ, ωσxσ,ασ, and the vσ = 1 ← 0 transition wavenumber associated with the intermolecular stretching mode νσ of each BHF by using two equivalent approaches. Both involved the assumption that the vibrational modes of the B and HF molecules were sufficiently stiff relative to the intermolecular stretching mode that BHF could be treated in a pseudo-diatomic approximation. One approach used derivatives of the potential evaluated at the distance r = re while the other used the potential constants obtained by non-linear regression fits of three analytical functions (Morse, Rydberg and Hulburt-Hirschfelder) to the ab initio calculated points. The two approaches would give exactly the same results if the functions were a perfect fit. The H-H function gave the best fit. The determined spectroscopic constants were found to be in reasonable agreement with the limited number available by experiment. The efficacy of the approach was tested for the diatomic molecule H35Cl by taking advantage of both an accurate RKR-type potential and an accurate set of spectroscopic constants. It was also established that the relationship De = kσ/(2a2) between two measures (De and kσ, both calculated ab initio) of the strength of the hydrogen bond in the BHF complexes (and required if the H-H function were an accurate representation of the BHF potential functions) holds to an excellent level of approximation, and supports the conclusion that this function is appropriate to represent the hydrogen bond in the complexes investigated.

The rotational spectrum of H2S⋯HI and an investigation by ab initio calculations of the origins of the observed doubling of rotational transitions in both H2S⋯HI and H2S⋯F2.

The rotational spectrum of the complex H2S⋯HI observed with a pulsed-jet, Fourier-transform microwave spectrometer shows that each rotational transition is split into a closely spaced doublet, a pattern similar to that observed earlier for the halogen-bonded complex H2S⋯F2. The origin of the doubling has been investigated by means of ab initio calculations conducted at the CCSD(T)(F12*)/cc-pVDZ-F12 level. Two paths were examined by calculating the corresponding energy as a function of two angles. One path involved inversion of the configuration at S through a planar transition state of C2v symmetry via changes in the angle ϕ between the C2 axis of H2S and the line joining the H and I nuclei [the potential energy function V(ϕ)]. The other was a torsional oscillation θ about the local C2 axis of H2S that also exchanges the equivalent H nuclei [the potential energy function V(θ)]. The inversion path is slightly lower in energy and much shorter in arc length and is therefore the favored tunneling pathway. In addition, calculation of V(ϕ) for the series of hydrogen- and halogen-bonded complexes H2S⋯HX (X = F, Cl, or Br) and H2S⋯XY (XY = Cl2, Br2, ClF, BrCl, or ICl) at the same level of theory revealed that doubling is unlikely to be resolved in these, in agreement with experimental observations. The barrier heights of the V(ϕ) of all ten complexes examined were found to be almost directly proportional to the dissociation energies De.

An ab initio investigation of alkali-metal non-covalent bonds BLiR and BNaR (R = F, H or CH3) formed with simple Lewis bases B: the relative inductive effects of F, H and CH3.

The alkali-metal bonds formed by simple molecules LiR and NaR (R = F, H or CH3) with each of the six Lewis bases B = OC, HCN, H2O, H3N, H2S and H3P were investigated by ab initio calculations at the CCSD(T)/AVTZ and CCSD(T)/awCVTZ levels of theory with the aim of characterising this type of non-covalent interaction. In some complexes, two minima were discovered, especially for those involving the NaR. The higher-energy minimum (referred to as Type I) for a given B was found to have geometry that is isomorphous with that of the corresponding hydrogen-bonded analogue BHF. The lower-energy minimum (when two were present) showed evidence of a significant secondary interaction of R with the main electrophilic region of B (Type II complexes). Energies DCBSe for dissociation of the complexes into separate components were found to be directly proportional to the intermolecular stretching force constant kσ The value of DCBSe could be partitioned into a nucleophilicity of B and an electrophilicity of LiR or NaR, with the order ELiH ⪆ ELiF = ELiCH3 for the LiR and ENaF > ENaH ≈ ENaCH3 for the NaR. For a given B, the order of the electrophilicities is ELiR > ENaR, which presumably reflects the fact that Li+ is smaller than Na+ and can approach the Lewis base more closely. A SAPT analysis revealed that the complexes BLiR and BNaR have larger electrostatic contributions to De than do the hydrogen- and halogen-bonded counterparts BHCl and BClF.

Isolation of a Halogen-Bonded Complex Formed between Methane and Chlorine Monofluoride and Characterisation by Rotational Spectroscopy and Ab Initio Calculations.

A halogen-bonded complex formed between methane and chlorine monofluoride has been isolated in the gas phase before the reaction between the components and has been characterised through its rotational spectrum, which is of the symmetric-top type but only exhibits K = 0 type transitions at the low effective temperature of the pulsed-jet experiment. Spectroscopic constants for two low-lying states that result from internal rotation of the CH4 subunit were detected for each of the two isotopic varieties H4C···35ClF and H4C···37ClF and were analysed to show that ClF lies on the symmetry axis with Cl located closer than F to the C atom, at the distance r0(C···Cl) ≅ 3.28 Å and with an intermolecular stretching force constant kσ ≅ 4 N m-1. Ab initio calculations at the explicitly correlated level CCSD(T)(F12c)/cc-pVTZ-F12 show that in the equilibrium geometry, the ClF molecule lies along a C3 axis of CH4 and Cl is involved in a halogen bond. The Cl atom points at the nucleophilic region identified on the C3 axis, opposite the unique C-H bond and somewhere near the C atom and the tetrahedron face centre, with re(C···Cl) = 3.191 Å. Atoms-in-molecules (AIM) theory shows a bond critical point between Cl and C, confirming the presence of a halogen bond. The energy that is required to dissociate the complex from the equilibrium conformation into its CH4 and ClF components is only De ≅ 5 kJ mol-1. A likely path for the internal rotation of the CH4 subunit is identified by calculations at the same level of theory, which also provide the variation of the energy of the system as a function of the motion along that path. The barrier to the motion along the path is only ≅ 20 cm-1.

Systematic behaviour of electron redistribution on formation of halogen-bonded complexes BXY, as determined via XY halogen nuclear quadrupole coupling constants.

Equilibrium nuclear quadrupole coupling constants associated with the di-halogen molecule XY in each of 60 complexes BXY (where B is one of the Lewis bases N2, CO, HCN, H2O, H2S, HCCH, C2H4, PH3, NH3 or (CH3)3N and XY is one of the di-halogens Cl2, BrCl, Br2, ICl, IBr or I2) have been calculated ab initio. The Townes-Dailey model for interpreting the changes in the coupling constants when XY enters the complex was used to describe the electron redistribution in the di-halogen molecule in terms of the fraction δi of an electron transferred from the Lewis base B to atom X and the fraction δp of an electron transferred simultaneously from atom X to atom Y. Systematic relationships between the δi values for the six series are established. It is shown that, in reasonable approximation, δi decays exponentially as the first ionisation energy IB of the Lewis base B increases, that is δi = A exp(-bIB). It is concluded from the results for the series BBrCl, BBr2, BICl, BIBr and BI2 that the coefficients A and b in regression fits to the corresponding logarithmic version ln(δi) = ln(A) -b(IB) of the equation are not strongly dependent on either the halogen atom X directly involved in the halogen bond in BXY or, for a given X, on the nature of Y. The behaviour of PH3 as a Lewis base appears to be anomalous. Values of δi and δp calculated by the quantum theory of atoms-in-molecules and natural bond orbital methodologies are very close to those from application of the Townes-Dailey approach described.

A chalcogen-bonded complex H3N⋯S=C=S formed by ammonia and carbon disulfide characterised by chirped-pulse, broadband microwave spectroscopy.

Ground-state rotational spectra were observed for ten symmetric-top isotopologues H3N⋯S=C=S, H3N⋯34S=C=S, H3N⋯S=C=34S, H3N⋯S=13C=S, H3 15N⋯S=C=S, H3 15N⋯34S=C=S, H3 15N⋯S=C=34S, H3 15N⋯S=13C=S, H3 15N⋯33S=C=S, and H3 15N⋯S=C=33S, the first five in their natural abundance in a mixture of ammonia and carbon disulphide in argon and the second group with enriched 15NH3. The four asymmetric-rotor isotopomers H2DN⋯S=C=S, H2DN⋯34S=C=S, H2DN⋯S=C=34S, and HD2N⋯S=C=S were investigated by using a sample composed of ND3 mixed with CS2. Rotational constants, centrifugal distortion constants, and 33S nuclear quadrupole coupling constants were determined from spectral analyses and were interpreted with the aid of models of the complex to determine its symmetry, geometry, one measure of the strength of the intermolecular binding, and information about the subunit dynamics. The complex has C3v symmetry, with nuclei in the order H3N⋯S=C=S, thereby establishing that the non-covalent interaction is a chalcogen bond involving the non-bonding electron pair of ammonia as the nucleophile and the axial region near one of the S atoms as the electrophile. The small intermolecular stretching force constant kσ = 3.95(5) N m-1 indicates a weak interaction and suggests the assumption of unperturbed component geometries on complex formation. A simple model used to account for the contribution of the subunit angular oscillations to the zero-point motion leads to the intermolecular bond length r(N⋯S) = 3.338(10) Å.

An Ab Initio Investigation of the Geometries and Binding Strengths of Tetrel-, Pnictogen-, and Chalcogen-Bonded Complexes of CO2, N2O, and CS2 with Simple Lewis Bases: Some Generalizations.

Geometries, equilibrium dissociation energies (De), and intermolecular stretching, quadratic force constants (kσ) are presented for the complexes B⋯CO2, B⋯N2O, and B⋯CS2, where B is one of the following Lewis bases: CO, HCCH, H2S, HCN, H2O, PH3, and NH3. The geometries and force constants were calculated at the CCSD(T)/aug-cc-pVTZ level of theory, while generation of De employed the CCSD(T)/CBS complete basis-set extrapolation. The non-covalent, intermolecular bond in the B⋯CO2 complexes involves the interaction of the electrophilic region around the C atom of CO2 (as revealed by the molecular electrostatic surface potential (MESP) of CO2) with non-bonding or π-bonding electron pairs of B. The conclusions for the B⋯N2O series are similar, but with small geometrical distortions that can be rationalized in terms of secondary interactions. The B⋯CS2 series exhibits a different type of geometry that can be interpreted in terms of the interaction of the electrophilic region near one of the S atoms and centered on the C∞ axis of CS2 (as revealed by the MESP) with the n-pairs or π-pairs of B. The tetrel, pnictogen, and chalcogen bonds so established in B⋯CO2, B⋯N2O, and B⋯CS2, respectively, are rationalized in terms of some simple, electrostatically based rules previously enunciated for hydrogen- and halogen-bonded complexes, B⋯HX and B⋯XY. It is also shown that the dissociation energy De is directly proportional to the force constant kσ, with a constant of proportionality identical within experimental error to that found previously for many B⋯HX and B⋯XY complexes.

What's in a name? 'Coinage-metal' non-covalent bonds and their definition.

Many complexes of the type BMX, (where B is a Lewis base such as H2, N2, ethyne, ethene, cyclopropane, H2O, H2S, PH3, or NH3, M is a coinage-metal atom Cu, Ag or Au, and X is a halogen atom) have now been characterised in the gas phase through their rotational spectra. It is pointed out that, for a given B, such complexes have angular geometries that are isomorphous with those of their hydrogen- and halogen-bonded counterparts BHX and BXY, respectively. Since the MX are, like the B, HX and XY referred to, closed-shell molecules, the complexes BMX also involve a non-covalent bond. Therefore, the name 'coinage-metal' bond is suggested for the non-covalent interaction in BMX, by analogy with hydrogen and halogen bonds. A generalised definition that covers all non-covalent bonds is also presented.

Dispersion and polar flattening: noble gas-halogen complexes.

High-level ab initio calculations on the complexes between noble gas atoms (He, Ne, Ar, Kr, and Xe) and dihalogen molecules (F2, Cl2, Br2, and I2) reveal trends, both in interaction energies and the energy difference between the linear and T-shaped structures, that can be explained well in terms of dispersion interactions enhanced by polar flattening of the halogens. The partial discrepancies with experimental findings are discussed. Graphical abstract The molecular electrostatic potential (red positive, blue negative) of Cl2...Br2 projected onto the 0.003 a.u. isodensity surface.

Molecular geometries and other properties of H2O⋯AgI and H3N⋯AgI as characterised by rotational spectroscopy and ab initio calculations.

The rotational spectra of H3N⋯AgI and H2O⋯AgI have been recorded between 6.5 and 18.5 GHz by chirped-pulse Fourier-transform microwave spectroscopy. The complexes were generated through laser vaporisation of a solid target of silver or silver iodide in the presence of an argon gas pulse containing a low concentration of the Lewis base. The gaseous sample subsequently undergoes supersonic expansion which results in cooling of rotational and vibrational motions such that weakly bound complexes can form within the expanding gas jet. Spectroscopic parameters have been determined for eight isotopologues of H3N⋯AgI and six isotopologues of H2O⋯AgI. Rotational constants, B0; centrifugal distortion constants, DJ, DJK or ΔJ, ΔJK; and the nuclear quadrupole coupling constants, χaa(I) and χbb(I) - χcc(I) are reported. H3N⋯AgI is shown to adopt a geometry that has C3v symmetry. The geometry of H2O⋯AgI is Cs at equilibrium but with a low barrier to inversion such that the vibrational wavefunction for the v = 0 state has C2v symmetry. Trends in the nuclear quadrupole coupling constant of the iodine nucleus, χaa(I), of L⋯AgI complexes are examined, where L is varied across the series (L = Ar, H3N, H2O, H2S, H3P, or CO). The results of experiments are reported alongside those of ab initio calculations at the CCSD(T)(F12*)/AVXZ level (X = T, Q).

Nucleophilicities of Lewis Bases B and Electrophilicities of Lewis Acids A Determined from the Dissociation Energies of Complexes B⋯A Involving Hydrogen Bonds, Tetrel Bonds, Pnictogen Bonds, Chalcogen Bonds and Halogen Bonds.

It is shown that the dissociation energy D e for the process B⋯A = B + A for 250 complexes B⋯A composed of 11 Lewis bases B (N2, CO, HC≡CH, CH2=CH2, C3H6, PH3, H2S, HCN, H2O, H2CO and NH3) and 23 Lewis acids (HF, HCl, HBr, HC≡CH, HCN, H2O, F2, Cl2, Br2, ClF, BrCl, H3SiF, H3GeF, F2CO, CO2, N2O, NO2F, PH2F, AsH2F, SO2, SeO2, SF2, and SeF2) can be represented to good approximation by means of the equation D e = c ' N B E A , in which N B is a numerical nucleophilicity assigned to B, E A is a numerical electrophilicity assigned to A, and c ' is a constant, conveniently chosen to have the value 1.00 kJ mol-1 here. The 250 complexes were chosen to cover a wide range of non-covalent interaction types, namely: (1) the hydrogen bond; (2) the halogen bond; (3) the tetrel bond; (4) the pnictogen bond; and (5) the chalcogen bond. Since there is no evidence that one group of non-covalent interaction was fitted any better than the others, it appears the equation is equally valid for all the interactions considered and that the values of N B and E A so determined define properties of the individual molecules. The values of N B and E A can be used to predict the dissociation energies of a wide range of binary complexes B⋯A with reasonable accuracy.

Cooperative hydrogen bonds form a pseudocycle stabilizing an isolated complex of isocyanic acid with urea.

The shapes of macromolecules and their complexes with small molecules are often determined by extended networks of hydrogen bonds. Here, for the first time, we provide a detailed description of a cooperative pair of hydrogen bonds to an individual molecule of urea. The structure and properties of a gas phase complex formed between urea and isocyanic acid are characterised through microwave spectroscopy and ab initio calculations at the CCSD(T)(F12*)/aug-cc-pVTZ level.

Tetrel, pnictogen and chalcogen bonds identified in the gas phase before they had names: a systematic look at non-covalent interactions.

The terms tetrel bond, pnictogen bond and chalcogen bond were coined recently to describe non-covalent interactions involving group 14, 15 and 16 atoms, respectively, acting as the electrophilic site that seeks a nucleophilic region of another molecule, for example a non-bonding electron pair or π-electron pair of a Lewis base. Many complexes containing these non-covalent bonds were identified and characterised in isolation in the gas phase by rotational and vibrational spectroscopy long before they were given these names. In this article, the geometries so determined for selected examples of complexes of each type are rationalised in terms of the molecular electrostatic surface potentials of the component molecules. Examples of chalcogen-bonded complexes considered are based mainly on sulfur dioxide, with the region near the sulfur atom as the electrophilic site that interacts with n-electron and π-electron pairs for a range of simple Lewis base molecules. For tetrel bonds, the examples discussed involve the carbon atom of carbon dioxide as the electrophilic centre, while for pnictogen bonds the central nitrogen of the closely related molecule nitrous oxide is chosen. Geometrical similarities within each series allow simple definitions of each type of non-covalent bond that are conformal with that recently advanced for the halogen bond, a related non-covalent interaction.

Geometries of H2S⋯MI (M = Cu, Ag, Au) complexes studied by rotational spectroscopy: The effect of the metal atom.

Complexes formed between H2S and each of CuI, AgI, and AuI have been isolated and structurally characterised in the gas phase. The H2S⋯MI complexes (where M is the metal atom) are generated through laser vaporisation of a metal rod in the presence of a low concentration of H2S and CF3I in a buffer gas of argon undergoing supersonic expansion. The microwave spectra of six isotopologues of each of H2S⋯CuI, H2S⋯AgI and three isotopologues of H2S⋯AuI have been measured by chirped-pulse Fourier transform microwave spectroscopy. The spectra are interpreted to determine geometries for the complexes and to establish the values of structural parameters. The complexes have Cs symmetry at equilibrium and have a pyramidal configuration about the sulfur atom. The local C2 axis of the hydrogen sulfide molecule intersects the linear axis defined by the three heavy atoms at an angle, ϕ = 75.00(47)° for M = Cu, ϕ = 78.43(76)° for M = Ag, and ϕ = 71.587(13)° for M = Au. The trend in the molecular geometries is consistent with significant relativistic effects in the gold-containing complex. The force constant describing the interaction between the H2S and MI sub-units is determined from the measured centrifugal distortion constant, ΔJ, of each complex. Nuclear quadrupole coupling constants, χaa(M) and χaa(I) (where M denotes the metal atom), are determined for H2S⋯CuI and H2S⋯AuI for the first time.