Hebi Bai

Coupling of a corona discharge to matrix isolation for the production of intermediates: the CCl4 system

Abstract An apparatus to couple a high voltage, low power corona discharge to a matrix isolation system has been designed and tested by application to the CCl 4 system. Argon was used as the discharge/expansion gas as well as the matrix material. A very high yield of the CCl 3 radical was obtained, along with a moderate yield of the CCl + 3 cation and related cationic species, along with several minor products. The results obtained here compare very favorably with earlier results from microwave discharge and excimer laser irradiation studies. The corona discharge is thus a simple, inexpensive and effective source of intermediates for matrix spectroscopic study.

Infrared spectroscopic investigation of complexes of ClF and Cl2 with crown ethers and related cyclic polyethers in argon matrices

Abstract The matrix isolation technique is employed to isolate and characterize 1:1 molecular complexes of 18-crown-6 and related cyclic polyethers with the reactive halogens ClF and Cl 2 in an inert environment. The dominant spectral feature noted for these complexes is the perturbed, red-shifted stretching mode of the halogen ion in the complex. Shifts are of the order of 100 cm −1 , which is similar to those observed for complexes of ClF with bases containing a single oxygen atom. The results suggest that there is no obvious reorganization of the host nor is there significant cooperativity of the oxygen atoms in the ring upon complexation. The absorption of the halogen in the complex is relatively broad compared to earlier studies of ClF complexes with simple bases.

Infrared matrix isolation of the 1:1 complexes of HCl and ClF with sulfur and nitrogen-containing macrocycles

Abstract The matrix isolation technique has been combined with IR spectroscopy to isolate and characterize 1 : 1 complexes of HCl, ClF and SO2 with cyclam, tetramethylcyclam and 1,4,8,11-tetra-thiacyclotetradecane (TTP). Each complex was characterized by a red shift of the acid subunit in the complex; for example the HCl stretch in its complex with TTP was observed at 2386 cm−1 while the ClF stretch in its complex with TTP came at 468 cm−1. These shifts, particularly for the ClF complex, were comparable to complexes with the monomer unit of the macrocycle (i.e. containing a single donor atom), which indicates that cooperativity is not an important factor in the formation of these complexes, in agreement with earlier studies of crown ether complexes.

Infrared spectroscopic characterization of molecular complexes of dimethylcadmium with Group V and VI hydrides in inert matrices and cryogenic thin films

Abstract Molecular complexes of (CH3)2Cd with H2S, H2Se, NH3, PH3 and AsH3 have been formed, isolated and characterized in argon matrices and cryogenic thin films. Infrared spectra of the 1:1 and, in some cases, the 1:2 complexes showed perturbations to a number of vibrational modes of the acid ((CH3)2Cd) and base subunits. Shifts between 6 and 22 cm−1 to the red of the CdC2 antisymmetric stretch were noted, suggesting that these complexes are someewhat less strongly bound than analogous complexes of (CH3)2Zn. This conclusion is supported by the relatively small shift of the symmetric deformation mode of NH3 complexes to (CH3)2Cd compared with many known complexes of NH3. Nonetheless, the magnitudes of the shifts correlate well with the proton affinities of the bases employed here. Cryogenic thin film experiments involving (CH3)2Cd and NH3 permitted initial formation and trapping of the 1:1 complex, and warming the film from 14 K towards room temperature led to formation of the 1:2 complex and then ultimately dissociation. The dissociation temperature correlated well with the shift of the CdC2 antisymmetric stretch, suggesting that both are related to the bond strength in the complex.

Infrared matrix isolation and cryogenic thin film spectroscopic study of molecular complexes of dimethylcadmium with group VI organics

Abstract Molecular complexes of (CH 3 ) 2 Cd with a series of alkyl derivatives containing different organic functional groups of the group VI elements have been formed, isolated and characterized in argon matrices and cryogenic thin films. For each system, a 1:1 complex was identified based on band positions and the product yield as a function of the concentrations of the two precursors in the reaction. For several systems, a 1:2 complex was observed as well at relatively high base/acid concentration ratios. Each complex was characterized by several perturbed vibrational modes, including the shifted CdC 2 antisymmetric stretching mode for all the complexes. Comparison of the band positions with those obtained in previous studies of related complexes indicates that (CH 3 ) 2 Cd is a very weak Lewis acid, yet these complexes are still stable under cryogenic conditions whether in solid argon or in solid thin films.

Matrix isolation study of the products and reactions pathways in the corona excited discharge of C6F6

Abstract Reactions and intermediates of C 6 F 6 and C 12 F 10 after exposure to a corona excited discharge have been studied by the trapping of products into an argon matrix at 14 K. Infrared spectroscopy was employed to identify product species. Several were known chemical species while assignments for several new species are proposed. Both isomerization and fragmentation reaction products were observed. All of the evidence points to formation of the very reactive C 6 F 5 radical as the initial product of excitation of C 6 F 6 although no product bands could definitively associated with this species.