Cooperative hydrogen bonding in thiazole⋯(H2O)2 revealed by microwave spectroscopy

Abstract

Two isomers of a complex formed between thiazole and two water molecules, thi···(H2O)2, have been identified through Fourier transform microwave spectroscopy between 7.0 and 18.5 GHz. The complex was generated by co-expansion of a gas sample containing trace amounts of thiazole and water in an inert buffer gas. For each isomer, rotational constants, A0, B0 and C0, centrifugal distortion constants, DJ, DJK, d1, d2, and nuclear quadrupole coupling constants, and , have been determined through fitting of a rotational Hamiltonian to the frequencies of observed transitions. The molecular geometry, energy, and components of the dipole moment of each isomer have been calculated using Density Functional Theory (DFT). The experimental results for four isotopologues of isomer I allow accurate determinations of the atomic coordinates of the oxygen atoms by r0 and rs methods. Isomer II has been assigned as the carrier of an observed spectrum on the basis of very good agreement between DFT-calculated results and spectroscopic parameters (including A0, B0 and C0 rotational constants) determined by fitting to measured transition frequencies. Non-covalent interaction (NCI) and natural bond orbital (NBO) analyses reveal that two strong hydrogen bonding interactions are present within each of the identified isomers of thi···(H2O)2. The first of these binds an H2O to the nitrogen of thiazole (OH···N) and the second binds the two water molecules (OH···O). A third, weaker interaction binds the H2O sub-unit to the hydrogen atom that is attached to C2 (for isomer I) or C4 (for isomer II) of the thiazole ring (CH···O).

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

“…[39] In order to perform the r 0 fit, geometrical parameters internal to each of the subunits, 2-ET and H 2 O, were assumed equal to their r e values calculated at the ωB97X-D/aug-cc-pVQZ level of theory. The r 0 fits of previous works [3,11,4] 5. The good agreement between r 0 and r e parameters is perhaps surprising.…”

“…The magnitude of E (2) indicates that the N•••H 1b -O1 hydrogen bond is stronger than the O1•••H 2b -O2 interaction which is consistent with an earlier study of thiazole•••(H 2 O) 2 . [11] The NBO analysis computed interaction energies of weaker hydrogen bonds between O atoms of the water molecules and hydrogen atoms on the ethyl group. The lone pair of O2 interacts principally with the antibonding orbital, σ*(C6-H6), with a much lesser contribution made by σ*(C7-H7).…”

“…In context of the described studies of monohydrates of methylated heteroaromatics, the significance of the present work is that it extends the range of systems characterised to include the mono-and dihydrate of a heteroaromatic that contains an alkyl group in the 2-position which is able to interact with the coordinating (isomer I). [11] The broad picture is that H 2 O molecules which hydrate imidazole and thiazole significantly affect the conformational and internal dynamics of substituents in the 2-and 4-positions of these heterocycles through weak hydrogen-bonding interactions.…”

Noncovalent interactions of aromatic heterocycles: rotational spectroscopy and theoretical calculations of the thiazole–CF4 and thiazole–SF6 complexes

“…[12][13][14] A number of model molecular complexes formed by aromatic heterocycles and associated counterparts have been investigated by rotational spectroscopy, aiming to determine the preferred non-covalent bonding topologies. Hydrogen bonds are usually the preferred interaction topologies in water or formic acid complexes with thiazole, 15,16 pyridine and its derivatives, [17][18][19][20] and thiophene derivatives. [21][22][23] The np* or pp* interactions overwhelm HBs in the formaldehyde complexes with pyridine 24 or benzofuran.…”

“…Thiazole is taken as the model heteroaromatics because of the multiple non-covalent bonding sites including the p-electrons and the N or S lone pairs as nucleophiles, and the C-H groups as electrophiles. 15,16,26,36…”