Rotational spectra and properties of complexes B⋯ICF3 (B = Kr or CO) and a comparison of the efficacy of ICl and ICF3 as iodine donors in halogen bond formation

Abstract

The ground-state rotational spectra of two weakly bound complexes B···ICF(3) (B = Kr or CO) formed by trifluoroiodomethane have been observed in pulsed jets by using two types of Fourier-transform microwave spectroscopy (chirped-pulse and Fabry-Perot cavity). Both complexes exhibit symmetric-top type spectra, thus indicating that the Kr atom in Kr···ICF(3) and both the C and O atoms in OC···ICF(3) lie along the C(3) axis of ICF(3). The rotational constant B(0), the centrifugal distortion constants D(J) and D(JK), and the iodine nuclear quadrupole coupling constant χ(aa)(I) were determined for each of the isotopologues (84)Kr···ICF(3), (86)Kr···ICF(3), (16)O(12)C···ICF(3), (16)O(13)C···ICF(3), and (18)O(12)C···ICF(3). Interpretation of the spectroscopic constants reveals that the carbon atom of CO is adjacent to I and participates in the weak bond in OC···ICF(3). Simple models based on unperturbed component geometries lead to the distances r(Kr···I) = 3.830(1) Å and r(C···I) = 3.428(1) Å in Kr···ICF(3) and OC···ICF(3), respectively, and to the quadratic force constants for stretching of the weak bond k(σ) = 2.80 N m(-1) and 3.96 N m(-1), respectively. The distances r(Z···I) (Z is the acceptor atom in B), the k(σ) values, and the angular geometries of the pair of complexes B···ICF(3) and B···ICl for a given B are compared when B = Kr, CO, H(2)O, H(2)S, or NH(3). The comparison reveals that the iodine bond in B···ICF(3) is systematically longer and weaker than that of B···ICl, while the angular geometry of the B···I moiety is isomorphic in B···ICF(3) and B···ICl for a given B. It is concluded that -CF(3) is less effective than -Cl as an electron-withdrawing group when attached to an I atom and that the angular geometries of the B···ICF(3) can be predicted by means of a simple rule that holds for many hydrogen- and halogen-bonded complexes.

The halogen bond between ethene and a simple perfluoroiodoalkane: C2H4⋯ICF3 identified by broadband rotational spectroscopy

“…It was recently shown that the complexes formed between CF 3 I and each of NH 3 and N(CH 3 ) 3 respectively contain halogen bonds, IÁ Á ÁN, with linear CAIÁ Á ÁN arrangements of atoms [2]. The length of the halogen bond in (CH 3 ) 3 NÁ Á ÁICF 3 is very similar to that associated with NÁ Á ÁI halogen bonds in crystal structures.…”

“…In each case, the iodine atom acts as electron acceptor for the coordinating NH 3 or N(CH 3 ) 3 Lewis base. It was shown [1,3] that H 2 S, H 2 O and CO respectively form halogen bonds to the iodine atom of CF 3 I in H 2 SÁ Á ÁICF 3 , H 2 OÁ Á ÁICF 3 and OCÁ Á ÁICF 3 . There are striking similarities between the structures of the BÁ Á ÁICF 3 complexes described above and comparators from the BÁ Á ÁIACl series where halogen bonding interactions result in the angle, \(CAIÁ Á ÁB)=180, in every case.…”

“…Recent work [1][2][3] in our group has examined complexes that contain prototypes of halogen bonding interactions that are significant in crystal engineering. Iodoalkanes and iodoperfluoroalkanes are attractive intermediates for use in synthetic chemistry owing to the ability of an iodine substituent to act as a leaving group [4].…”

“…The length of the halogen bond in (CH 3 ) 3 NÁ Á ÁICF 3 is very similar to that associated with NÁ Á ÁI halogen bonds in crystal structures. Spectra of OCÁ Á ÁICF 3 and KrÁ Á ÁICF 3 were interpreted to reveal similarities [3] between trends in BÁ Á ÁICl (where B is a simple Lewis base) and BÁ Á ÁICF 3 . The described OCÁ Á ÁICF 3 , KrÁ Á ÁICF 3 , H 3 NÁ Á ÁICF 3 and (CH 3 ) 3 NÁ Á ÁICF 3 complexes are either linear or symmetric tops containing a linear halogen bond such that \(CAIÁ Á ÁB) is equal to 180°.…”

Infrared and Raman Measurements of Halogen Bonding in Cryogenic Solutions

“…Before discussing the methodology used and the results obtained during the cryospectroscopic experiments, it is worth noting that, since the first experiments reported in 2009 [48], a variety of complexes strongly related to those studied in the cryosolutions have now also been investigated using traditional and chirped-pulsed microwave studies [49][50][51][52][53][54][55], and that additional information on complexes between more complex perfluoro alkyl iodides and pyridine has also been obtained using low-temperature IR and NMR experiments [56].…”