Hydrogen Bonding and Molecular Geometry in Isolated Hydrates of 2-Ethylthiazole Characterised by Microwave Spectroscopy

Broadband microwave spectra of the isolated 2-ethylthiazole molecule, and complexes of 2-ethylthiazole⋅⋅⋅H2O and 2-ethylthiazole⋅⋅⋅(H2O)2 have been recorded by probing a gaseous sample containing low concentrations of 2-ethylthiazole and water within a carrier gas undergoing supersonic expansion. The identified conformer of the isolated 2-ethylthiazole molecule and the 2-ethylthiazole sub-unit within each of 2-ethylthiazole⋅⋅⋅H2O and 2-ethylthiazole⋅⋅⋅(H2O)2 have C1 symmetry. The angle that defines rotation of the ethyl group relative to the plane of the thiazole ring, ∠(S-C2-C6-C7), is -98.6(10)° within the isolated 2-ethylthiazole molecule. Analysis of molecular geometries and non-covalent interactions reveals each hydrate complex contains a non-linear primary, N⋅⋅⋅Hb-O, hydrogen bond between an O-H of H2O and the nitrogen atom while the O atom of the water molecule(s) interacts weakly with the ethyl group. The ∠(Hb⋅⋅⋅N-C2) parameter, which defines the position of the H2O molecule relative to the thiazole ring, is found to be significantly greater for 2-ethylthiazole⋅⋅⋅H2O than for thiazole⋅⋅⋅H2O. The distance between the O atoms is determined to be 2.894(21) Å within the dihydrate complex which is shorter than observed within the isolated water dimer. The primary hydrogen bond within 2-ethylthiazole⋅⋅⋅(H2O)2 is shorter and stronger than that in 2-ethylthiazole⋅⋅⋅H2O as a result of cooperative hydrogen bonding effects.

Equivalent and Complement of the ω-Bonding Model and Charge-Shift Bonding Model: A Natural Bond Orbital/Natural Resonance Theory/Atoms in Molecules Investigation via Cu/Ag/Au Bonding in BMX (B = H2O, H2S, NH3, and PH3; M = Cu, Ag, and Au; and X = F, Cl, Br, and I)

Chemical bonding is the language of logic for chemists. Two new resonance bonding models, ω-bonding and charge-shift (CS) bonding, are gaining popularity among chemists. This study investigated the Cu/Ag/Au bonding in BMX (B = H₂O, H₂S, NH₃, and PH₃; M = Cu, Ag, and Au; and X = F, Cl, Br, and I) complexes using natural bond orbital (NBO) analysis, natural resonance theory (NRT), and atoms in molecules (AIM) method. The main aim is to reveal the relation between ω-bonding model and CS bonding model via Cu/Ag/Au bonding. Our studies demonstrate that the Cu/Ag/Au bonds exhibit the characteristics of both ω-bonding and CS bonding. Further studies found that ω-bonding and CS bonding models are equivalent and complement each other in understanding the studied Cu/Ag/Au bonding. Another interesting finding is the implication of the omega symbol in the ω-bonding model. These findings could help to promote the communication and CS bonding understanding of many more similar ω-bonded complexes.

Theoretical investigation on the nature of substituted benzene⋯AuX interactions: covalent or noncovalent?

The nature of interactions between AuX (X = F, Cl, Br, CN, NO2, CH3) and aromatic moieties with different electronic properties has been investigated for possible tuning of coinage–metal bonds by varying the substituents.

Non-Covalent Interactions of the Lewis Acids Cu–X, Ag–X, and Au–X (X = F and Cl) with Nine Simple Lewis Bases B: A Systematic Investigation of Coinage–Metal Bonds by Ab Initio Calculations

The equilibrium geometry and two measures (the equilibrium dissociation energy in the complete basis set limit, De(CBS) and the intermolecular stretching force constant kσ) of the strength of the non-covalent interaction of each of six Lewis acids M–X (M = Cu, Ag, Au) with each of nine simple Lewis bases B (B = N2, CO, HCCH, CH2CH2, H2S, PH3, HCN, H2O, and NH3) have been calculated at the CCSD(T)/aug-cc-pVTZ level of theory in a systematic investigation of the coinage–metal bond. Unlike the corresponding series of hydrogen-bonded B⋯HX and halogen-bonded B⋯XY complexes (and other series involving non-covalent interactions), De is not directly proportional to kσ. Nevertheless, as for the other series, it has been possible to express De in terms of the equation De = cNB.EMX, where NB and EMX are the nucleophilicities of the Lewis bases B and the electrophilicities of the Lewis acids M–X, respectively. The order of the EMX is determined to be EAuF > EAuCl > ECuF > ECuCl > EAgF ≈ EAgCl. A reduced electrophilicity defined as (EMX/σmax) is introduced, where σmax is the maximum positive value of the molecular electrostatic surface potential on the 0.001 e/bohr3 iso-surface. This quantity is, in good approximation, independent of whether F or Cl is attached to M.

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.

Rotational spectra and theoretical study of tetramers and trimers of 2-fluoroethanol: dramatic intermolecular compensation for intramolecular instability

Cooperativity and chirality dominate in stabilizing the 2-fluoroethanol tetramer, thanks to a fully bifurcated C–H⋯F H-bond network.

The covalent interaction between dihydrogen and gold: A rotational spectroscopic study of H2-AuCl

The pure rotational transitions of H2-AuCl have been measured using a pulsed-jet cavity Fourier transform microwave spectrometer equipped with a laser ablation source. The structure was found to be T-shaped, with the H-H bond interacting with the gold atom. Both 35Cl and 37Cl isotopologues have been measured for both ortho and para states of H2. Rotational constants, quartic centrifugal distortion constants, and nuclear quadrupole coupling constants for gold and chlorine have been determined. The use of the nuclear spin-nuclear spin interaction terms Daa, Dbb, and Dcc for H2 were required to fit the ortho state of hydrogen, as well as a nuclear-spin rotation constant Caa. The values of the nuclear quadrupole coupling constant of gold are χaa=-817.9929(35) MHz, χbb=504.0(27) MHz, and χcc=314.0(27). This is large compared to the eQq of AuCl, 9.63 312(13) MHz, which indicates a strong, covalent interaction between gold and dihydrogen.

H3PAgI: generation by laser-ablation and characterization by rotational spectroscopy and ab initio calculations

The new compound H₃P···AgI has been synthesized in the gas phase by means of the reaction of laser-ablated silver metal with a pulse of gas consisting of a dilute mixture of ICF₃ and PH₃ in argon.

The new compound H₃P···AgI has been synthesized in the gas phase by means of the reaction of laser-ablated silver metal with a pulse of gas consisting of a dilute mixture of ICF₃ and PH₃ in argon. Ground-state rotational spectra were detected and assigned for the two isotopologues H₃P···¹⁰⁷AgI and H₃P···¹⁰⁹AgI in their natural abundance by means of a chirped-pulse, Fourier-transform, microwave spectrometer. Both isotopologues exhibit rotational spectra of the symmetric-top type, analysis of which led to accurate values of the rotational constant B₀, the quartic centrifugal distortion constants D_J and D_JK, and the iodine nuclear quadrupole coupling constant χ_aa(I) = eQq_aa. Ab initio calculations at the explicitly-correlated level of theory CCSD(T)(F12*)/aug-cc-pVDZ confirmed that the atoms P···Ag–I lie on the C₃ axis in that order. The experimental rotational constants were interpreted to give the bond lengths r₀(P···Ag) = 2.3488(20) Å and r₀(Ag–I) = 2.5483(1) Å, in good agreement with the equilibrium lengths of 2.3387 Å and 2.5537 Å, respectively, obtained in the ab initio calculations. Measures of the strength of the interaction of PH₃ and AgI (the dissociation energy D_e for the process H₃P···AgI = H₃P + AgI and the intermolecular stretching force constant F_P···Ag) are presented and are interpreted to show that the order of binding strength is H₃P···HI < H₃P···ICl < H₃P···AgI for these metal-bonded molecules and their halogen-bonded and hydrogen-bonded analogues.