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The cocondensation reactions of nickel, palladium, and platinum atoms with gaseous oxygen or dilute oxygen-argon mixtures at 4.2-10 "K give rise to binary transition metal dioxygen complexes. Variable concentration and diffusion controlled warm up studies, 160/'80 isotopic substitution studies, normal coordinate and isotope intensity calculations establish the complexes to be of the types M(0,) and (Oz)M(02). Both the mono-and bisdioxygen complexes contain the dioxygen molecules coordinated to the metal atom in a side-on fashion, with a unique Dzd "spire"-type structure favored for the biscomplexes. Frequency and bond stretching force constant trends within the series of complexes are examined and suggest that the 0-0 and M-0 values increase with increasing coordination number, and thus with an increase in partial positive charge on the metal. This trend in 0-0 stretching frequencies is not in accord with the evaluation of metal-dioxygen bond strengths as based on the degree of reversibility of dioxygen coordination.

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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 ...

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