The cocondensation reactions of Co atoms with CO at 6-15 K are investigated for the first time using matrix infrared, Raman, uv-visible, and ESR spectroscopy. Using extremely low Co concentrations (Co:M ~1:104 to 1:10s) which are shown to favor the formation of mononuclear complexes, variable concentration l2Cl60-M experiments (where M = Ne, Ar, Kr, or Xe), 12C160-13Cl60 and ,2Cl60-l2C,80-M mixed isotopic substitution, in conjunction with matrix warm-up experiments, the reaction products are shown to be Co(CO)" (where = 1-4). The vibrational spectroscopic data and isotope frequency calculations for Co(12Cl60)"(,3Cl60),»_" (where = 0-4) in carbon monoxide matrices favor a Cy-trigonally distorted tetrahedral structure for Co(CO)4. The corresponding ESR spectrum supports the contention that the molecule has axial symmetry and 5 = % The spin-Hamiltonian parameters are g$ = 2.007 ± 0.010, g± = 2.128 ± 0.010, A||(S9Co) = (58 ± 1) X 10-4 cm-1, and A j_(s9Co) = (55 ± 1) X 10-4 cm-1 and are found to be consistent with a Cy trigonal distortion. Striking confirmation of the C3" distortion is obtained from the 13C hyperfine splitting of Co(l3C,60)4 in 93% ,3C160. The corresponding uv-visible spectrum displays ligand field and charge transfer bands in the region 200-350 nm. The appropriate relationship between the electronic and magnetic parameters of C3t Co(CO)4 provides an order of magnitude estimate for the ligand field parameter and predicts the 2Ai -2E d-d transition in the range 300-350 nm. The ESR data for Co(CO)4 in Ar matrices provide evidence for two forms of the molecule, Co(CO)4 (I) and Co(CO)4 (II). Both molecules appear to have axial symmetry and S = >/2 but with different spin-Hamiltonian parameters and different 13C hyperfine splittings. Co(CO)4 (I) is favored on deposition at 6-8 K while Co(CO)4 (II) predominates upon annealing the matrix to [30][31][32][33][34][35] K. An analysis of the data is not totally unambiguous, although the ESR parameters for Co(CO>4 in Ar matrices can be interpreted in terms of two isomeric forms of Co(CO)4, one having a Cy distortion (I) and the other a Did distortion (II). The observed higher stability of molecule II in Ar supports the conclusions drawn from minimum internal energy molecular orbital calculations which favor the Did configuration. Infrared isotope frequency calculations were performed for the C3,., (I) and Did (II) isomeric forms of Co( l2Cl60)"(13Cl60)4-n (where = 0-4) in Ar matrices. In contrast to the data for Co(CO)4 in CO matrices, the compared frequencies for Cy and Did Co(CO)4 in Ar matrices fit the experimental data equally well and reinforce the conclusions drawn from the corresponding ESR data. The vibrational data for Co(COb in inert gas matrices suggest that the molecule has a regular triangular planar Dy, structure. However, the absence of observable l3C hyperfine splitting in the corresponding Co(,3Cl60)3 ESR spectrum implies that Co(CO)3 is most probably distorted away from planar toward a Cy trigonal pyramidal structure. The vibrational data for ...

Using transition metal diatom synthetic techniques the elusive binuclear carbonyl complexes Rh2(C0)8 and Ir2(C0)8 are shown by infrared spectroscopy to be the products (along with the respective mononuclear complexes Rh(CO), and Ir(CO),) of the 15'K matrix cocondensation reactions of Rh and Ir atoms with pure CO, under conditions of high metal concentrations. The binuclear octacarbonyl complexes are also formed in the matrix dimerization reactions 2Rh(C0)4 -Rh2(C0)8 and 2Ir(C0)4 -Ir2(CO)* at 45-50'K. A simple analysis of the statistical and surface reaction pathways to M2(C0)8 and M(CO), is presented and leads to binuclear-mononuclear concentration ratios which are proportional to the metal/CO matrix ratio. Using these techniques, the effect of varying the metal/CO matrix ratio on the relative absorbances of the appropriate spectral bands was investigated for the Rh-CO reaction in the range 1/10 to l/lOOO. The results provide convincing evidence for the binuclear octacarbonyl formulation. By comparison with dicobalt octacarbonyl, the complexes Rh2(CO)s and Irp(CO)a are found to exist in the bridge bonded form, Rhn(C0)s disproportionating under dynamic vacuum conditions to bridge bonded Rh4(C0)12 at about -48°C and Ir2(CO)s similarly to bridged bonded Ir4(CO)12 at about -58'C, indicating that under comparable conditions Irs(CO)s is somewhat less stable than Rhn(C0)s. Evidence for the nonbridged (by analogy with Co.(CO)s, high temperature) isomer was not obtained for Rhp(C0)s or Ir,(CO)*, probably because of the instability of the bridge bonded (low temperature) isomer with respect to disproportionation to the tetranuclear cluster complex. The low temperature stability of Rh*(C0)8 and Ir2(CO)8 is certainly consistent with the difficulties previously experienced by various groups of workers who attempted to synthesize and characterize the complexes by room temperature techniques.ntil very recently, dicobalt octacarbonyl, in its

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