The nu(CO) vibrational spectra of planar transition metal carbonyl clusters

The nu(CO) vibrational spectra of planar transition cluster carbonyls containing M(CO)(4) groups are studied. It is possible to anticipate qualitatively, both for the infrared and Raman, the band intensity changes associated with increasing metallic nature of the cluster. These enable a unification of the band patterns shown by the species reported. As for (idealized) spherical clusters, the spherical harmonic model (SHM), suitably modified, becomes of more general applicability as cluster size increases, although for smaller species the tensor harmonic model (THM) makes a contribution.     

Application of the Spherical Harmonic Model to the ν(CO) Vibrational Spectra of Some Fe(CO)4 and M(CO)5 (M=Cr, W) Transition Metal Cluster Carbonyl Species

When the Fe(CO)₄ and M(CO)₅ (M=Cr, W) groups are co-ordinated in C_3v and C_4v fashion, respectively, in transition metal carbonyl cluster species they contain two sets of non-symmetry related carbonyl groups. In the application of the spherical harmonic model (SHM) to the interpretation of the infrared spectra of these compounds it proves necessary first to treat these as for a normal, isolated, M(CO)₄ or M(CO)₅ group and then apply the SHM. This recognition gives insights into the general application of the SHM.     

KARMEN time anomaly: search for a neutral particle of mass 33.9 MeV in pion decay

We have searched for the pion decay pi(+)-->&mgr;+X, where X is a neutral particle of mass 33.905 MeV. This process was suggested by the KARMEN Collaboration to explain an anomaly in their observed time distribution of neutrino induced reactions. Having measured the muon momentum spectrum of charged pions decaying in flight, we find no evidence for this process and place an upper limit on the branching fraction eta相似文献   

Gas-phase structures of 1-adamantylphosphines,PH<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>(1-Ad)<Subscript>3−<Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1–3)

The gas-phase structure of 1-adamantylphosphine has been determined by electron diffraction, supplemented with data from ab initio and DFT calculations. The adamantyl fragment was modeled with local C _3v symmetry and the phosphino group was found to be in a position almost bisecting a mirror plane of the adamantyl group, giving the molecule overall approximate C _s symmetry. There is a small displacement of the C–P bond from the local threefold axis of the adamantyl group. Geometry optimizations were also performed for bis-(1-adamantyl)phosphine (C ₁ point-group symmetry) and tris-(1-adamantyl)phosphine (C ₃ symmetry), demonstrating extremely crowded environments around the phosphorus atoms leading to adamantyl groups that were much less symmetric. The adamantyl groups were also found to twist by a significant amount to minimize the strain.     

Identification of the IR frequencies of the interstitial carbon atom in some M6C (M = Fe,Ru) carbonyl clusters by13 C-enrichment

¹³C-enriched carbido carbonyl clusters of the type [M₆C(CO) _n ] ^z? (M=Fe,n=16,z=2; M=Ru,n=16 ifz=2 andn=17 ifz=0) have been prepared and their IR spectra observed in the 900?600 cm^?1 region; the band shifts occurring upon¹³ C substitution enable the assignment to the stretching modes of the interstitial C atom. Band patterns reflect the symmetry of the M₆C core, but the frequencies seem dependent on other molecular features.     

Crystal and molecular structure of 2,2′-bipyridyl-(μ3-1-keto-2,3,4-triphenylcyclobutenyl) dicarbonylbromomolybdenum(1)benzene [(C6H5)3C3CO](C10H8N2)(CO)2MoBr·C6H6

The crystal structure of [(C₆H₅)₃C₃CO](C₁₀H₈N₂)(CO)₂MoBr·C₆H₆ has been determined. The complex crystallizes in the triclinic space groupP ¯1 witha=8.52(1),b=19.42(3),c=10.54(1) Å, =97.4(1), =74.6(1), and =87.5(1)°. There are two formula units per cell. A total of 2924 unique observed reflections was collected photographically using CuK radiation. The structure was refined toR=0.072. The molybdenum atom in this compound can be considered as situated at the center of a very distorted octahedron. The six coordination sites about the metal atom are occupied by two carbonyl groups which share with the bipyridyl the four equatorial positions. The bromine and a -bonded keto-triphenylcyclobutenyl ring take up the two axial positions. There is an ³ interaction between the cyclobutenyl ring and the molybdenum atom. The detailed geometry of the 1-keto-2,3,4-triphenylcyclobutenyl ligand is similar to that found by Coffey (1962) in a cobalt complex. In the present compound the cyclobutenyl ring is slightly puckered with a dihedral angle of 11.05° between the plane which contains the allylic carbon atoms and that containing the ketonic group. Two solvating benzene molecules are centered at the inversion sites in the unit cell.     

Vibrational frequencies associated with the inter-stitial carbon atoms in the large metal cluster complexes (NMe4)2[Os10C(CO)24] and H2Os10C(CO)24

Determination of the vibrational frequencies of the interstitial carbon atoms in the metal clusters [Os₁₀C(CO)₂₄]^2? and H₂Os₁₀C(CO)₂₄, confirmed in the latter by ¹³C enrichment, shows that the protonated cluster species exhibits considerable deviation from pseudo-cubic symmetry in the crystal, in contrast to the dianion.