Microwave Spectra and Gas-Phase Structural Parameters of Bis(η⁵-cyclopentadienyl)tungsten Dihydride

Abstract

Microwave spectra for 11 isotopomers of bis(η 5 -cyclopentadienyl)tungsten dihydride ((C 5 H 5 ) 2 WH 2 ) were recorded in the 5-14 GHz region using a Flygare-Balle-type pulsed beam spectrometer. Spectra arising from four tungsten isotopomers of both the (C 5 H 5 ) 2 WH 2 and (C 5 H 5 ) 2 WHD species and three W isotopomers for the (C 5 H 5 ) 2 WD 2 complex have been measured. The ∼250 b-type transition frequencies assigned for these near-prolate asymmetric top molecules were accurately described (σ fit ) 2-4 kHz) using the rotational parameters A, B, and C and one centrifugal distortion constant, ∆ J . The small value obtained for ∆ J indicates a fairly rigid structure. From a least-squares fit using the resulting 33 rotational constants to obtain the molecular structure, we were able to determine the W-H bond length, r(W-H) ) 1.703(2) Å, the H-W-H bond angle, ∠(H-W-H) ) 78.0(12)°, the W-Cp centroid distance, r(W-Cp) ) 1.940(8) Å, the angle made by the Cp centroids with tungsten, ∠(Cp-W-Cp) ) 155(2)°, and the average C-C bond length, r(C-C) ) 1.429(8) Å. The hydrogen atom separation is r(H-H) ) 2.14(2) Å, indicating that this is clearly a "classical dihydride" rather than an "η 2 -dihydrogen" complex. The WH 2 moiety parameters determined from Kraitchman's equations (r(W-H) ) 1.682(2) Å, ∠(H-W-H) ) 78.6(2), r(H-H) ) 2.130(2) Å) agree well with the least-squares results. Furthermore, the r e parameters obtained from DFT calculations agree well with the experimental r 0 structural parameters. To our knowledge, this work marks the first microwave study of a bent-metallocene complex. The present measurements were made with a pulsed-beam Fourier transform spectrometer employing a homodynetype detection system, and this configuration is described. This homodyne system greatly simplifies the microwave circuit, with no apparent loss in sensitivity.

Microwave spectra and structure of the cyclopropanecarboxylic acid-formic acid dimer

“…Microwave measurements were made using a Flygare-Balle type pulsed-beam Fourier transform (PBFT) microwave spectrometer described previously. 21,22 The CPCA (95%) and FA (98%) samples were purchased from Sigma Aldrich and the FA-d 1 (99.2% d) was purchased from CDN isotopes; each sample was used without further purification. The samples were transferred to separate glass sample cells.…”

Identification and characterization of 1,2-BN cyclohexene using microwave spectroscopy

“…The spectrometers are similar to the Flygare-Balle microwave spectrometer system, but employ homodyne (zero-IF) detection method, the details of which can be found in previous papers. 22,23 . Initial scans were made from 7200 to 6700 MHz covering the J″=0→J′ =1 a-dipole and b-dipole transitions using the low resolution transverse beam spectrometer.…”

Gas phase measurements of mono-fluoro-benzoic acids and the dimer of 3-fluoro-benzoic acid

“…This spectrometer was described previously. 20,21 The microwave pulses, for microwave transmit, tune the cavity and trigger the acquisition, and valve pulses are produced by custom boards that use transistor-transistor logic (TTL) off-the-shelf chips. The control of the spectrometer and these pulses is made in either manual or computer controlled mode.…”