M. L. Caste, C. J. Cairns, J. S. Church, W. K. Lin, J. C. Gallucci, D. H. Busch

A low-spin cobalt(II) complex of an unsaturated, 16-membered tetradentate macrocycle containing four imine donors has been synthesized by reaction of the protonated ligand with cobalt(II) under basic conditions. The tetradentate ligand rapidly rearranges in the presence of cobalt(II) to give a product in which one of the secondary amines, which are usually peripheral substituents, becomes coordinated as an appended axial imine group. An X-ray crystal structure determination has confirmed the nature of this rearrangement. [3-(1-(Methylamino)ethylidene)-11-(1-(methylimino)ethyl)-2,12-dimethyl-1,5,9,13- tetraazacyclohexadeca-1,4,9,12-tetraene-κ4N]cobalt(II) hexafluorophosphate-acetonitrile crystallizes in the monoclinic space group P2₁/n with a = 18.186 (2) Å, b = 7.296 (1) Å, c = 25.279 (3) Å, and β = 110.66 (1)°. The structure was solved by the heavy-atom method and refined to final agreement indices of R = 6.0% and Rw = 11.6% for 2922 reflections. The macrocyclic ligand occupies five vertices of a slightly distorted square pyramid, with an acetonitrile of solvation weakly interacting at the sixth coordination site. Spectroscopic and electrochemical studies on the cobalt(II) complex, and on the chemically oxidized cobalt(III) product, confirm that the cyclidene ligand retains its structure in solution.

P. Groner, J. S. Church, Y. S. Li, J. R. Durig

The microwave spectrum of ethyldifluorophosphine, CH₃CH₂PF₂, has been investigated in the region from 18.0 to 39.5 GHz. The spectra of two conformers have been identified. The ground state and seven vibrationally excited states have been assigned for the more stable gauche conformer (phosphorus lone pair with respect to CH₃ group), whereas the ground state and one excited state have been assigned for the trans form. Rotational and most quartic centrifugal distortion constants have been determined with A=6784.501(3), B=2930.156(2), C=2352.576(2) MHz for gauche and A=5444.910(3), B=3290.133(3), C=2871.915(3) MHz for trans, both in the ground state. Electric dipole moments were obtained from ground state Stark effect measurements: ‖ μ_a‖=1.990(4), ‖ μ_b‖=0.855(4), ‖ μ_c‖=0.091(7), ‖ μ_t‖=2.168(2) D for gauche and ‖ μ_a‖=1.780(10), ‖ μ_b‖=0, ‖ μ_c‖=1.077(10), ‖ μ_t‖=2.081(10) D for trans. Using a new computer program, a diagnostic least‐squares fit of the structural parameters suggests significant structural differences between the conformers, notably the C–C–P angle which changes from 110.7° in the gauche form to 114.9° in the trans form. From a temperature study of the microwave spectrum, it was found that the gauche conformer is at least 80 cm⁻¹ (229 cal/mol) more stable than the trans conformer. These results are compared to similar quantities in some corresponding molecules.

J. R. Durig, Y. S. Li, J. F. Sullivan, J. S. Church, C. B. Bradley

The microwave spectra of CH₃CH₂SnH₃ and CH₃CH₂SnD₃ for the five most abundant isotopes of naturally occurring tin, ¹¹⁶Sn, ¹¹⁷Sn, ¹¹⁸Sn, ¹¹⁹Sn, and ¹²⁰Sn, have been recorded in the range 18.0–40.0 GHz. Only a‐type transitions were identified and R‐branch assignments have been made for the ground vibrational state. The components of the dipole moment were determined from the Stark effect to be ‖μ_a‖=0.86±0.01 D, ‖μ_b‖=0.48±0.04 D, and ‖μ_t‖=0.99±0.02 D. No splittings in the ground state were observed due to the internal rotation of either the SnH₃ or CH₃ tops. Based on this observation, lower limits to the barriers to internal rotation of 1.12 and 2.12 kcal/mol are estimated for the SnH₃ and CH₃ tops, respectively. The following five structural parameters were determined from a least‐squares fit of the 20 rotational constants (B and C only): r(Sn–C)=2.143±0.003 Å; r(C–C) =1.552±0.025 Å; ∢HSnC=109.5±0.1°; ∢HCH=107.5±3.9°; ∢SnCC=112.6±0.9°. The Raman spectra (3200–10 cm⁻¹) were obtained for all three phases and infrared spectra (3200–80 cm⁻¹) were obtained for the gas and solid. An assignment is proposed based on band contours, depolarization values, isotopic shifts, and group frequencies for all the normal modes except the two internal torsions; however, the methyl torsion in CH₃CH₂SnD₃ has been tentatively assigned to a band observed at 242 cm⁻¹ in the infrared spectrum of the solid. A normal coordinate calculation was carried out by utilizing a modified valence force field with 30 internal coordinates and 21 force constants. The observed frequencies are fit to better than 1%. The observed splitting of the normal modes in the spectra of the solids along with the number of observed lattice modes is consistent with two molecules per primitive cell. The results are compared to corresponding quantities in some similar molecules.

J. R. Durig, J. S. Church, Y. S. Li

The microwave spectra of H₃SiSiH₂I and D₃SiSiD₂I have been recorded from 26.5 to 38.5 GHz. a-Type transitions were observed, and R-branch assignments have been made for the ground vibrational state. The rotational constants were found to have the following values: for H₃SiSiH₂I, A = 8602.22 ± 8.63, B = 1179.79 ± 0.02, C = 1062.47 ± 0.02 MHz; for D₃SiSiD₂I, A = 6571.01 ± 5.80, B = 1078.87 ± 0.03, C= 969.96 ± 0.06 MHz. From a diagnostic least-squares adjustment to fit the six rotational constants, the following structural parameters were obtained: r(Si-H₃) = 1.491 ± 0.010 Å, r(Si-H₂)= 1.478 ± 0.010 Å, r(Si-Si) = 2.336 ± 0.007 Å, r(Si-I) = 2.440 ± 0.009 Å, ∠SiSiI = 106.7 ± 0.3°, ∠SiSiH(I) = 111.8 ± 1.8°, ∠SiSiH = 111.3 ± 1.9°. These parameters are compared to the corresponding ones in some other silanes. The quadrupole coupling constants were found to have the values χ_a = -938, χ_bb = 255, and χ_cc = 683 MHz with η = -428 MHz. The infrared (3500-20 cm^-1) and Raman spectra (3500-0 cm^-1) have been recorded for both the gas and solid. Additionally, the Raman spectra of the liquids were recorded and qualitative depolarization values were obtained. All of the normal modes except the SiH₃ torsion have been assigned on the basis of band contours, depolarization values, and group frequencies. A normal-coordinate calculation has been carried out by utilizing a modified valence force field to calculate the frequencies and the potential energy distribution. Some mixing was found among the SiH₃ symmetric deformation, the SiH₂ scissors, and the SiH₂ wagging motions. These results are compared to similar quantities in some corresponding molecules.

J. R. Durig, P. A. Brletic, J. S. Church, Y. S. Li

The microwave spectra of SiH₃SiH₂¹²C¹⁴N and SiH₃SiH₂¹²C¹⁵N have been recorded from 18.0 to 26.5 GHz. Only a‐type transitions were observed and R‐branch assignments have been made for the ground vibrational state. The rotational constants were found to have the following values: for SiH₃SiH₂¹²C¹⁴N, A = 8996.72±5.91, B = 2203.95±0.05, and C = 1844.03±0.05 MHz; for SiH₃SiH₂¹²C¹⁵N, A = 8896.08±5.70, B = 2145.15±0.04, and C = 1798.63±0.03 MHz. From a diagnostic least‐squares adjustment to fit the six rotational constants, the following structural parameters were obtained: r(Si–Si) = 2.332±0.014 Å; r(Si–C) = 1.841±0.015 Å; r(C≡N) = 1.156±0.010 Å; and ∢SiSiC = 107.4±0.1°. These parameters are compared to the corresponding ones in some other silanes and cyanide molecules. The infrared (2500 to 80 cm⁻¹) and the Raman (2500 to 10 cm⁻¹) spectra of the solid phase have been recorded for disilanyl cyanide‐d₀ and ‐d₅. Additionally, the infrared spectrum of the gaseous phase and the Raman spectrum of the liquid phase were recorded and qualitative depolarization values were obtained. All of the normal modes have been assigned based upon band contours, depolarization ratios, and group frequencies but the assignment of the SiH₃ torsional mode must be considered tentative. A normal coordinate calculation has been carried out by utilizing a modified valence force field to calculate the frequencies and the potential energy distribution. These results are compared to similar quantities in some corresponding molecules.

J. R. Durig, P. A. Brletic, J. S. Church

The infrared (3500-40 cm^-1) and Raman (3500-10 cm^-1) spectra have been recorded for the gaseous and solid phases of methacryloyl fluoride. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. The asymmetric potential function for internal rotation of the O=C-F top has been determined from far infrared data, and the following potential constants have been evaluated: V₁ = 257±4; V₂ = 1582±6; and V₃ = 173±3 cm^-1. From these data, the s-trans conformer was determined to be the predominant rotamer at ambient temperature with the other conformer being the s-cis; the enthalpy difference between the s-trans and s-cis conformers is 430 cm^-1 (1230 cal/mol). This value compares well with the value of 444 cm^-1 (1270 cal/mol) obtained for the liquid from a variable temperature study of the Raman spectrum. The methyl torsional barrier was also calculated from the far infrared data to be 1.77 kcal/mol. A vibrational assignment and values for the thermodynamic functions of gaseous methacryloyl fluoride are presented.

J. R. Durig, J. S. Church

The vibrational spectra of gaseous and crystalline CH₃CH₂OCH₂CH₃ and CD₃CD₂OCH₂CH₃ have been investigated below 500 cm⁻¹. Assignments of the low frequency fundamentals of the trans-trans and trans-gauche conformers are presented. Several torsional series were observed for the methyl groups in the far infrared spectra of the gaseous compounds. These series were analyzed using both coupled and uncoupled top treatments. No potential coupling was found; however, kinetic coupling of the two tops is evident. The low frequency spectra of the two crystalline phases were recorded. That of the stable modification was interpreted in terms of the non-centric space group P2₁2₁2₁ ≡ D⁴₂. In the metastable phase, there are two molecules per unit cell each of which occupy equivalent sites of C_s, C₂ or C₁ symmetry. Several lattice modes have been observed in the Raman spectra of each crystalline phase and tentative assignments are proposed.

J. R. Durig, J. S. Church

The Raman spectra of gaseous disilane and disilane-d₆ as well as the Raman and infrared spectra of their crystalline solids at 20 K have been recorded from 25 to 3500 cm^-l. Two quantum torsional transitions of the SiH, moiety were observed at 233 and 251 cm^-1 in the Raman spectrum of gaseous disilane. A barrier to internal rotation of 439± 10 cm^-1 (1.26 kcal/mol) has been calculated based on these frequencies. The crystalline modification of disilane at 20 K was shown to belong to the monoclinic space group P₂₁/c ≡ C_2h⁵. There are two molecules per unit cell each of which sits on identical C_i sites. The results of normal coordiante analyses of H₃SiSiH₃ H₃SiNCO, and H₃SiNCS are presented and the force fields obtained for the H₃Si moieties are compared.