Spectra and structure of gallium compounds: Part VII. Microwave,infrared and raman spectra and normal coordinate analysis of trimethylamine-trimethylgallane

The infrared (100–3500 cm^?1) and Raman (25–3200 cm^?1) spectra of the solid phases of (CH₃)₃NGa(CH₃)₃ and (CH₃)₃¹⁵NGa(CH₃)₃ have been recorded near liquid nitrogen temperatures as well as the Raman spectrum (100–3200 cm^?1) of the liquid phase at ~50°C and the low resolution microwave spectrum (26.5–39.0 GHz) of (CH₃)₃NGa(CH₃)₃. The spectra have been interpreted on the basis of C_3v molecular symmetry and a vibrational assignment is proposed for all but the torsional modes. The B value calculated from the microwave spectrum is consistent with published structural parameters reported from an electron diffraction study. A modified valence force field has been used to calculate the observed frequencies and the potential energy distribution. The force constants presented are consistent with changes in the structural parameters of the Lewis acid and base upon adduct formation. Extensive mixing has been observed among the low-frequency modes. The Ga-N stretching force constant (1.6 mdyn A^?1) has a value intermediate between those of (CH₃)₃NGaH₃ and H₃NGa(CH₃₃).The lack of apparent factor group splitting indicates that only one molecule occupies each primitive cell, situated on either a C₃ or C_3v site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

Spectra and structure of gallium compounds: Part VI. Infrared and Raman spectra of trimethylgalliumtrimethylphosphine

The infrared (50–4000 cm^?1 ) and Raman (50–3500 cm^?1) spectra of (CH₃)₃GaP(CH₃)₃ have been recorded for the solid state at the temperature of boiling liquid nitrogen. The spectra have been interpreted on the basis of C_3v molecular symmetry and a complete vibrational assignment except for the methyl torsional modes is presented. A modified valence force field model has been utilized in calculating the frequencies and potential energy distribution. The calculated potential constants for the adducts are compared to those previously reported for the Lewis acid and the Lewis base moieties and the differences are shown to be consistent with structural changes upon adduct formation. Extensive coupling has been observed between the Ga-P stretching mode and the PtC₃ and GaC₃ deformational modes. Substantial coupling is also observed between the PC₃ and the GaC₃ rocking motions. The magnitude of the Ga-P stretching force constant is found to be much smaller (0.88 mdyn Å^?1) than that reported for (CH₃)₃PGaH₃ and the difference possibly reflects the relative stabilities of the donor-acceptor bond in the two complex species.The fact that none of the A, modes appear as doublets in the spectra, nor are any of the E modes split except for the GaC₃ antisymmetric stretch, which is believed to be due to the two isotopes of gallium, indicates that there is only one molecule per primitive cell sitting on a C_3v or C₃ site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCF?MO?LC?(LCGO) Methode. X. Das Methylkation (CH3)+

The (CH₃)⁺ has been investigated ab initio, taking all 8 electrons into account, using the Allgemeines Programmsystem/SCF ? MO ? LC (LCGO ) Verfahren. After varying the C? H distance and the position of the C atom, it was found that the (CH₃)⁺ ion is planar with a bond distance of R_CH = 2.05 a.u. The force constants (C? H stretching, angular vibration) were computed to be k₁ = 18.9 mdyn/Å, and the associated frequencies to be ω₁ = 3256 cm^?1 and ω₂ = 1526 cm^?1. The ionization energy was found to be I = 25.75 eV. The electron affinity was estimated to be A = 5.4 eV.     

Vibro-conformational behaviour and normal coordinate analysis of fluorocarbonyl isocyanate,FC(O)NCO

Vibrational data of vapour, liquid and matrix-isolated fluorocarbonyl isocyanate, FC(O)NCO, were investigated. A subsequent normal coordinate analysis was performed for the A′ species of the predominant planar cis conformer (CO double bond cis with respect to the vicinal NC double bond). The following internal force constants were derived: f_CO= 12.88 mdyn Å⁻¹, f_CF=6.20 mdyn Å⁻¹ and F_CN= 4.42 mdyn Å⁻¹.     

Spectra and structure of phosphorus-boron compounds: VII. Vibrational analysis of solid phosphine-borane

The infrared (70–2700 cm^?) and Raman (25–2500 cm^?1) spectra of H₃PBH₃, H₃PBD₃, D₃PBH₃ and D₃PBD₃ in the solid state at ?196 °C have been recorded. The shift associated with the boron-10 and boron-11 isotopes was observed for the P-B stretching motion. A complete vibrational assignment is proposed and a normal coordinate calculation utilizing a valence force field model has been carried out. The force constant of 1.97 mdyn Å^?1 for the phosphorus-boron stretching mode is consistent with the relatively long phosphorus-boron bond; this constant is compared to the similar quantity for several other phosphorus-boron compounds. None of the E modes for the “free” molecule were found to be split. The number of observed lattice modes is not consistent with the crystal structure previously reported for this molecule. A possible explanation is discussed.     

A new approach to electron diffraction analysis of symmetric triatomic molecules with large-amplitude bending motion: The equilibrium geometry,force field and vibrational frequencies of BaI2 as determined by electron diffraction

Diffraction data on BaI₂, analyzed by a new approach, indicate an anharmonic potential with a barrier of 71(12) cm^?1 at a linear geometry. The structural and vibrational parameters were found to be r_e^h(Ba-I_o) = 3.150(7)Å, ∠_eIBaI = 148.0(9) °, f_q = 0.69(8) mdyn/Å,f_qq= 0.14(6) mdyn/Å, k₂ = ?0.0075(15) mdyn/Å, k₄ = 0.0025(9) mdyn/ų, v₁ = 106(12) cm^?1 and v₃ = 145(21) cm^?1. The bending frequency v₂ is predicted to be near 16 cm^?1.     

Vibrational force fields and amplitudes,and zero-point average structures of (CH3)3Y molecules (Y = N,P, As,Sb, Bi): A Combination of electron-diffraction and spectroscopic data

Following the development of methods for placing electron-diffraction and spectroscopic geometrical parameters on a common basis, available data on (CH₃)₃Y molecules (Y = N, P, As, Sb, Bi) have been used to derive force fields, r.m.s. amplitudes of vibration u along the internuclear vectors, and perpendicular amplitude correction coefficients K for these molecules. For trimethylamine, the amplitudes are similar whether or not off-diagonal elements are included in the force field; hence, only diagonal elements are considered for the other molecules. Among the interesting trends, as group V is descended, is that the C-Y r.m.s. amplitudes increase only from 0.049 to 0.058 Å, whereas the C-Y stretching force constant decreases by over 60% from 5.3 to 1.8 mdyn Å^?1. There is evidence for an increasing tendency for torsional motion of methyl groups, as group V is descended.For each of the molecules, the amplitude data were used to derive zero-point average (r^o_α) structures and to make estimates of a partial equilibrium (r_e) structure. For trimethylamine the results suggest a systematic error in the electron-beam wavelength of the literature study, and the structural parameters were appropriately revised. The r^o_α lengths of the C-Y bonds in the five molecules are 1.458 ± 0.002, 1.844 ± 0.003, 1.979 ± 0.010, 2.169 ± 0.010 and 2.263 ± 0.004 Å, respectively. The estimated r_e parameters for the bonds in trimethylamine agree well with the microwave r_s structure.     

The preparation and structures of Ph3AsGaI3 and [Ph3AsI][GaI4]

Colourless crystals of Ph₃AsGaI₃ (1) have been prepared by reaction of triphenylarsine with GaI₃·OEt₂ in diethyl ether. The structure of 1, in which the length of the AsGa donor-acceptor bond is 2.490(2) Å, has been determined by an X-ray diffraction study. In contact with the solvent phase, 1 is transformed into yellow crystals of [Ph₃AsI][GaI₄], 2 which has been structurally characterised by Raman spectroscopy (AsI stretching at 196 cm⁻¹) and by X-ray diffraction. The salt 2 is the first arsenic(V) iodo complex to have been examined crystallographically; the AsI bond distance is 2.485(1) Å.     

Investigations of the Nature of ZnII−SiII Bonds

A series of zinc(II) silylenes was prepared by using the silylene {PhC(NtBu)₂}(C₅Me₅)Si. Whereas reaction of the silylene with ZnX₂ (X=Cl, I) gave the halide‐bridged dimers [{PhC(NtBu)₂}(C₅Me₅)SiZnX(μ‐X)]₂, with ZnR₂ (R=Ph, Et, C₆F₅) as reagent the monomers [{PhC(NtBu)₂}(C₅Me₅)SiZnR₂] were obtained. The stability of the complexes and the Zn?Si bond lengths clearly depend on the substitution pattern of the zinc atom. Electron‐withdrawing groups stabilize these adducts, whereas electron‐donating groups destabilize them. This could be rationalized by quantum chemical calculations. Two different bonding modes in these molecules were identified, which are responsible for the differences in reactivity: 1) strong polar Zn?Si single bonds with short Zn?Si distances, Zn?Si force constants close to that of a classical single bond, and strong binding energy (ca. 2.39 Å, 1.33 mdyn Å^?1, and 200 kJ mol^?1), which suggest an ion pair consisting of a silyl cation with a Zn?Si single bond; 2) relatively weak donor–acceptor Zn?Si bonds with long Zn?Si distances, low Zn?Si force constants, and weak binding energy (ca. 2.49 Å, 0.89 mdyn Å^?1, and 115 kJ mol^?1), which can be interpreted as a silylene–zinc adduct.     

An electron-diffraction study of the molecular structure of gaseous perbromyl fluoride and calculation of its force field and vibrational amplitudes

The molecular structure of FBrO₃ has been studied by gas-phase electron diffraction. Least-squares refinements of the molecular geometry using fixed spectroscopic amplitudes revealed two geometrical minima. Initially, the amplitudes employed were derived from diagonal force fields obtained by spectroscopic least-squares refinements to fit observed and calculated wave numbers; for each geometry there are two spectroscopic minima. In the lowest geometrical minimum the wave number agreement is poor, however, the introduction of the ∠OBrO/∠FBrO interaction force constant removed the discrepancies; the resulting force field is F(Br-O) = 6.92 ± 0.02 mdyn Å^?1F(Br-F) = 3.22 ± 0.03 mdyn Å^?1, F(∠OBrO) = 1.06 ± 0.02 mdyn Å, F(∠FBrO) = 0.81 ± 0.03 mdyn Å, F(∠OBrO/∠FBrO) = ?0.19 ± 0.02 mdyn Å. In the corresponding geometrical minimum r_g(Br-O) = 1.582 ± 0.001 Å, r_g(Br-F) = 1.708 ± 0.003 Å, r_α(∠OBrO) = 114.9 ± 0.3°, r_α(∠FBrO) = 103.3 ± 0.3°. Perpendicular amplitude correction coefficients, calculated for each force field employed, were used throughout to relate the interatomic distances through the r_α-structure. The geometries of the r_α^o- and r_e-structures are estimated.     

Selenostannate aus wäßriger Lösung: Darstellung und Struktur von Na4SnSe4 · 16 H2O

Selenostannates from Aqueous Solutions: Preparation and Structure of Na₄SnSe₄ · 16 H₂0 Pure selenostannates(IV) are prepared from aqueous solutions by reaction of SnSe₂, with alkali selenides, strictly excluding oxygen. Na₄SnSe₄ · 16 H₂O, being obtained from stoicheo-metric 1:2 quantities, is characterized by a complete X-ray structure analysis and by vibrational spectra. The compound is monoclinic (P2₁/m) with a = 8.673(3), b = 16.563(4), c = 8.647(2) Å, β = 92.10(2)°, Z = 2; it contains isolated tetrahedral SnSe₄^4? ions [Sn? Se 2.504(2)?2.527(2) Å, Se? Sn? Se 106.6(1)?111.1(1)°] which are in contact to the hydrated octahedral [Na(OH₂)₆]⁺ ions through Se…?H? O bridges within an extensive hydrogen bridge system. The stretching vibrations of the SnSe₄^4? ion are observed at 195 (n?₁) and 252 cm^?1 (n?₃). The stretching force constant is approximately 1.59 mdyn/Å.     

Structural chemistry of bimetallic hydride complexes of titanium and aluminium: I. Crystal and molecular structure of [(η5-C5H5)2,Ti(μ-H)2AlH2]2(CH3)2NCH2CH2N(CH3)2C6H6

The structure of a titanium aluminium hydride complex of composition [(C₅H₅)₂TiAlH₄]₂(CH₃)₂NC₂H₄N(CH₃)₂C₆H₆ has been determined by X-ray diffraction. The complex forms triclinic crystals with unit cell dimensions a = 8.406(2), b = 10.117(2), c = 11.269(3) Å; α = 112.01(2)°, β = 109.25(2)°, γ = 87.04(2)°, space group P$\text{1}$, Z = 2 and density d = 1.21 g/cm³. The structure was refined to give a discrepancy index R = 0.056. The crystals are composed of centrosymmetric molecules of (Cp₂TiAlH₄)₂TMEDA (Cp = η⁵-cyclopentadienyl) and molecules of crystal benzene. Two moieties of Cp₂TiH₂AlH₂ are linked by a tetramethylethylenediamine molecule (r_AlN 2.11 Å). The aluminium atom is bonded to a titanium atom by a double hydride bridge (r_AlH b = 1.8, 1.6 Å, r_TiH b = 1.6 Å), and has trigonal bipyramidal stereochemistry, [H₄N] (r_AlH t = 1.6 Å).     

Piperazine Functionalization of C70 for Incorporation into Supramolecular Assemblies

The photochemical reaction of piperazine with C₇₀ produces a mono‐adduct (N(CH₂CH₂)₂NC₇₀) in high yield (67 %) along with three bis‐adducts. These piperazine adducts can combine with various Lewis acids to form crystalline supramolecular aggregates suitable for X‐ray diffraction. The structure of the mono‐adduct was determined from examination of the adduct I₂N(CH₂CH₂)₂NI₂C₇₀ that was formed by reaction of N(CH₂CH₂)₂NC₇₀ with I₂. Crystals of polymeric {Rh₂(O₂CCF₃)₄N(CH₂CH₂)₂NC₇₀}_n?nC₆H₆ that formed from reaction of the mono‐adduct with Rh₂(O₂CCF₃)₄ contain a sinusoidal strand of alternating molecules of N(CH₂CH₂)₂NC₇₀ and Rh₂(O₂CCF₃)₄ connected through Rh?N bonds. Silver nitrate reacts with N(CH₂CH₂)₂NC₇₀ to form black crystals of {(Ag(NO₃))₄(N(CH₂CH₂)₂NC₇₀)₄}_n?7nCH₂Cl₂ that contain parallel, nearly linear chains of alternating (N(CH₂CH₂)₂NC₇₀ molecules and silver ions. Four of these {Ag(NO₃)N(CH₂CH₂)₂NC₇₀}_n chains adopt a structure that resembles a columnar micelle with the ionic silver nitrate portion in the center and the nearly non‐polar C₇₀ cages encircling that core. Of the three bis‐adducts, one was definitively identified through crystallization in the presence of I₂ as ¹²{N(CH₂CH₂)₂N}₂C₇₀ with addends on opposite poles of the C₇₀ cage and a structure with C_2v symmetry. In ¹²{I₂N(CH₂CH₂)₂N}₂C₇₀, individual ¹²{I₂N(CH₂CH₂)₂N}₂C₇₀ units are further connected by secondary I2???N2 interactions to form chains that occur in layers within the crystal. Halogen bond formation between a Lewis base such as a tertiary amine and I₂ is suggested as a method to produce ordered crystals with complex supramolecular structures from substances that are otherwise difficult to crystallize.     

Transition-metal complexes of two valence tautomers of a bulky phenoxide, 2,6-Bu-t2-4-MeC6H2O− (ArO−); preparation and crystal and molecular structure of a phenoxytitanium(III) and a cyclohexadienonylrhodium(I) complex, [Ti(η-C5H5)2 OAr] and [Rh(ArO-η5)(PPh3)2]

The 2,6-di-t-butyl-4-methylphenoxo ligand (ArO^?) is ambidentate, giving rise to the O-bonded 15-electron d¹ [Ti(η-C₅H₅)₂OAr] and the η⁵ -[C(2)-C(6)]-bonded 18-electron d⁸ complex [Rh(ArO-η⁵)(PPh₃)₂], obtained from [{Ti(η-C₅H₅)₂Cl}₂]-LiO Ar and [Rh{N(SiMe₃)₂}(PPh₃)₂]-ArOH, respectively; the average TiC(η) distance is 2.362(10) Å, TiO 1.892(2) Å, and O:C(of Ar) 1.352(3) Å, and TiOC 142.3(2)°; in the Rh^I complex, C(2)C(6) are coplanar (with CC(av.) 1.38(2) Å). C(1)O 1.28 Å, and Rh to C(2) C(6) bond lengthsare in the range 2.19–2.65 Å.     

The enthalpies of formation of CH3Mn(CO)5 and of CH3Re(CO)5, and the strengths of the CH3Mn and CH3Re bonds

From measurements of the heats of iodination of CH₃Mn(CO)₅ and CH₃Re(CO)₅ at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔH^o_f[CH₃Mn(CO)₅, c] = ?189.0 ± 2 kcal mol^?1 (?790.8 ± 8 kJ mol^?1), ΔH^o_f[Ch₃Re(CO)₅,c] = ?198.0 ± kcal mol^?1 (?828.4 ± 8 kJ mo^?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn₂(CO)₁₀ and Re₂(CO)₁₀, values are derived for the dissociation energies: D(CH₃Mn(CO)₅) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol^?1 and D(CH₃Re(CO)₅) = 53.2 ± 2.5 kcal mol^?1. In general, irrespective of the value accepted for D(MM) in M₂(CO)₁₀, the present results require that, D(CH₃Mn) = $\text{1}\text{2}$D(MnMn) + 18.5 kcal mol^?1 and D(CH₃Re) = $\text{1}\text{2}$D(ReRe) + 30.8 kcal mol^?1.     

The preparation,properties and crystal structure of bis(η5-cyclopentadienyldicarbonyliron)dimethylgermyl]oxide, [(η5-C5H5)(CO)2FeGe(CH3)2]2O

One of the main products of oxidation of (η⁵-C₅-H₅)₂Fe₂(CO)₃Ge(CH₃)₂ by air has been shown to be [(η⁵-C₅H₅)(CO)₂FeGe(CH₃)₂]₂O. The infrared, NMR and mass spectra are consistent with this formula and the detailed structure has been established by X-ray crystallography. In polar solvents the NMR suggests the existence of major and minor conformers interconverting only slowly on the NMR time scale at ≈ 25°. The X-ray diffraction study has shown the compound to consist of two (η⁵-C₅H₅)(CO)₂FeGe(CH₃)₂ moieties joined by a bridging oxygen atom. Two rotational isomers are present in the unit cell in a disordered fashion. Some pertinent average distances and angles are: FeGe, 2.372 Å; GeO, 1.785 Å; GeOGe′, 134°. The compound crystallizes in the monoclinic system, space group P2₁/n, with a 8.056(2), b 12.506(2), c 22.631(3) Å, β 98.01(1)°, d_calc 1.692 g cm^?3. Counter data were collected using Mo-K_α radiation. The 1780 reflections above background were used in least-squares refinement which converged at R₁ = 0.051 and R₂ = 0.068.     

Antiferromagnetic complexes involving metalmetal bonds : I. Synthesis and molecular structure of an antiferromagnetic dimer with a CrCr bond

The binuclear complex (C₅H₅)₂Cr₂(S)(SCMe₃)₂ was prepared by refluxing a solution of chromocene and t-butylmercaptane in heptane. The structure of the product was determined by single crystal X-ray diffraction. The chronium atoms are linked by a sulphide bridge (SCr 2.24 Å;, <CrSCr 74.1° and two SCMe₃ bridges (CrS 2.38 Å;, <CrSCr 68.3–69.3°). The two cyclopentadienyl ligands (CC 1.41 Å;, CrC 2.23 Å;) are in apical positions, their ring planes being parallel to each other. The complex is an antiferromagnet (?2J cm^?1) despite the small CrSCr angles and short chromiumchromium distance (2.689 Å;) indicative of strong CrCr bonding.     

Studies on organometallic compounds with hetero multiple bridges : V. Crystal and molecular structure of the parent rhenium complex Re2Br2(CO)6(THF)2 and substituted products of tricarbonylrhenium(I) derived from it

Reactions of the tetrahydrofuran adduct Re₂Br₂(CO)₆(THF)₂ with some phosphorous- and nitrogen-containing donors under mild conditions are reported, which led to the formation of substituted products of tricarbonylrhenium(I). Bromide abstraction from the THF adduct by secondary amines and CS₂ produced the dithiocarbamato derivatives Re(S₂CNR₂)(CO)₃(HNR₂) whose behaviour in solution with CO was also investigated. Mass spectral data for some of the substituted products have been measured. The title compound crystallizes in the space group P2₁/n with cell constants a = 8.661(2), b = 11.251(3), c = 11.424(3) Å and β = 110.36(2)°, U = 1043.67 ų and D_calc = 2.686 g cm^?3, Z = 2. The molecule consists of a planar Re₂Br₂ moiety, as demanded by symmetry. The two THF groups are on opposite sides of this plane and the three CO groups around each rhenium atom are arranged in a fac arrangement. The unique ReBr distances are 2.642(5) and 2.644(4)Å, while the ReO distance is 2.129(31) Å. The ReBrRe and BrReBr angles are 97.3(2) and 82.7(1)°, respectively. The Re?Re nonbonding distance is 3.967(3) Å. The THF ligands consist of a nearly planar C₄ fragment (maximum deviation from planarity 0.06 Å), while the oxygen is 0.348 Å out of that plane, the angle defined by the C₄ plane and the COC fragment of the THF ligand being 24.99°. Final values of the discrepancy indices are R(F) = 0.074 and R_w(F) = 0.095.     

Synthesis and molecular structure of niobocene trimethylacetate and its π-complex with diphenylacetylene

Niobocene trimethylacetate Cp₂Nb(OOCCMe₃) (I) does not react with usual n-donors (pyridine and triphenylphosphine), but readily adds a π-acceptor molecule of diphenylacetylene (tolane) in benzene to form Cp₂Nb(OOCCMe₃)(π-Ph₂C₂) · 0.5 C₆H₆ (II). The structures of the diamagnetic complexes I and II have been determined by an X-ray diffraction study. These molecules represent wedge-like sandwiches wit dihedral angles between cyclopentadienyl ligands equal to 44.4 and 50.7°, and average NbC distances of 2.39 and 2.44 Å, respectively. The bisector plane of I contains the chelate trimethylacetate group (NbO bond lenghts 2.23 and 2.24 Å) and that of II contains the coordinated tolane molecule and the oxygen atom of the terminal trimethylacetate ligand (NbO 2.16, NbC 2.18 and 2.19, CC 1.29 Å, PhCC angles 141 and 146°). An unusually large splitting of OCO stretching frequencies is observed in the IR spectrum of I (1652?1305 = 347 cm^?1). Structural characteristics of the coordinated CC triple bond in II are similar to those found in Cp(π-Ph₄C₄)Nb(CO)(π-Ph₂C₂) studied earlier. The role played by the Nb^III lone pair in I and II is discussed.     

Structural and infrared spectroscopic characterization of Co6C(CO)12S2: a high-nuclearity carbido carbonyl cluster spontaneously formed from dicobalt octacarbonyl and carbon disulphide

Co₆C(CO)₁₂S₂ (I) has been isolated in crystalline form from the mixture of more than a dozen of carbonyl products formed when Co₂(CO)₈ reacts at room temperature with CS₂. Crystals of I are monoclinic with space group Cc, and lattice constants a  16.250(5), b  9.413(4), c  16.036(5) Å, β  116.77(4)°. Structure refinement gave R  0.034 for 1974 reflections. The CCo₆S₂ core of the molecule possesses idealized D_3h geometry. It is composed of a Co₆ trigonal prism, enclosing a C atom in the centre, and the triangular faces are capped symmetrically by the two S atoms. The core contains two sorts od CoCo distances: short one (2.432 Å) along the triangular edges, and long ones (2.669 Å) along the lateral edges. The average CoC distance is 1.94 Å, and the average CoS distance 2.192 Å.¹³CO-enriched samples were prepared photochemically and their IR spectra used in the assignment of the CO stretching frequencies. The CO stretching force constant was calculated to be 1670(2) Nm^-1.By the use of ¹³CS₂, I has also been obtained in a selectively carbido-¹³C-labelled form. The vibrational frequencies of the carbide atom were observed, and that at 819 cm^-1 (¹³C: 790 cm^-1) assigned to the species

, and that at 548 cm^-1 (¹³C: 535.5 cm^-1) to species E′. For the Co-C(carbide) force constant a value of 155 Nm^-1 was calculated. The cobalt—sulphur stretching frequencies were found at 309 cm^-1 (

) and 239 cm^-1 (E′). The CoS stretching force constant, 78 Nm^-1, is considerably lower than that obtained for SCo₃-(CO)₉, viz. 112 Nm^-1.