Metal molecules, matrix isolation

The preparation of polysiloxane-V2 via microscaie metal vapor-matrix isolation as well as gram, synthetic-scale rotary solution reactor techniques is described. Consideration of the two different-scale processes reflects both the initial preparation of the molecule and demonstrates the utility of a combined, complementary matrix-/macrosynthetic approach. ... 

Work has also been conducted that involved the investigation, via infrared spectroscopy, of matrix-isolated, plutonium oxides (40), with the appropriate precautions being taken because of the toxicity of plutonium and its compounds. A sputtering technique was used to vaporize the metal. The IR spectra of PuO and PUO2 in both Ar and Kr matrices were identified, with the observed frequencies for the latter (794.25 and 786.80 cm", respectively) assigned to the stretchingmode of Pu 02. Normal-coordinate analysis of the PUO2 isotopomers, Pu 02, Pu 02, and Pu 0 0 in Ar showed that the molecule is linear. The PuO molecule was observed in multiple sites in Ar matrices, but not in Kr, with Pu 0 at 822.28 cm" in the most stable, Ar site, and at 817.27 cm" in Kr. No evidence for PuOa was observed. 

It is worth noting, prior to citing actual metal atom studies, the recent secondary ion mass spectrometry (SIMS) on an argon matrix-isolated propene sample, demonstrating the applicability of SIMS analysis to the characterization of matrix-isolated species. The same group h s reported the first C NMR spectra of organic molecules trapped in an argon matrix. ... 

Matrix isolation studies usually permit spectroscopic observation of the species M(CO), M(CO)2,. M(CO) , the coordinatively saturated molecule. In some early studies, species thought to be simple unsaturated carbonyls were in fact carbonyls of metal clusters Mx(CO) a very low concentration of metal in the matrix (e.g., I mol in 104 mol noble gas) has to be used to prevent clustering. All the partially coordinated carbonyls are only matrix species, that is, they only exist when completely isolated from other molecules of their own kind or from CO. The coordinately saturated carbonyls are of more interest in the context of this review. The following new molecules have been reported Au(CO)2 (84a) Ag(CO)3, Cu2(CO)6 (46, 87) Pd(CO)4 (22), Pt(CO)4 (69) Rh2(CO)g, Ir2(CO)g (37) M(CO)6[M = Pr, Nd, Gd, Ho, Yb (100), Ta (24), U (117)]. The Cu, Pd, Pt, Rh, and Ir carbonyls can be obtained by condensing the metal vapors with pure CO at 40 K and then pumping off excess CO to leave a film of the carbonyl. The Cu, Pd, and Pt carbonyls decompose under vacuum temperatures above -100°C, and the Rh and Ir carbonyls dimerize with loss of CO to give M4(CO)12 above -60°C. The gold and silver carbonyls are not stable outside matrix isolation conditions. Unfortunately, the literature is presently unclear about the stability of the Ta and lanthanide hexacarbonyls outside a matrix. 

Matrix isolation methods of synthesis have also been used to prepare and study coordination compounds. These involve the vaporization of a metal and a potential ligand, which are then rapidly carried in a stream of inert gas to a very cold surface, where the compound which has been formed is quickly trapped in the solid matrix. It is possible to determine the type of bonding, the structure and the thermodynamic properties of the compounds formed. Only small ligand molecules have been used thus far carbon monoxide, nitric oxide, nitrogen and oxygen, for example, but molecules of great interest have been formed. Some such are [Pd(C2H4)], [Pd(N2)3], [Ni(N2)202], [Ni(N2)4] and [Ni(CO)(N2)3].41... 

In 1975, Perutz and Turner reported the first detailed and systematic matrix-isolation study 28) of noble gas coordination to transition metal centers in an investigation that followed the UV/visible photochemistry of M(C0)6 (M = Cr, Mo, and W) in noble gas, methane, and otiier matrices at 4 and 20 K. By comparing the IR spectra obtained with CO-enriched metal hexacarbonyls with the results of EFFF calculations 29), it was deiuonstrated that, upon short-wavelength UV photolysis of M(CO)e in the matrix, a molecule of CO was ejected and a M(CO)6 fragment with square-pyramidal (C4 ) geometry was produced. The... 

In this paper we will present some examples of the application of resonance Raman spectroscopy to the study of transition metal diatomics. The application of Raman spectroscopy to matrix-isolated metal clusters was first reported by Schulze et al. (] ). Having observed only a single line in the Raman spectrum of Ag3, Schulze concluded that the molecule was linear since a bent triatomic and an equilateral triangular geometry would have, in principle, 3 and 2 Raman-active modes. The evidence, however, is not conclusive since many Czy molecules have very weak asymmetric stretches in the Raman ( ) (for example, the V3 mode of O3 is undetectable in the Raman (3 )). Moreover, the bend (V2) of Ag3 is expected to be a very low-frequency mode, perhaps lower than one can feasibly detect in a matrix Raman experiment. 

The matrix isolation technique has been applied, in conjunction with the salt/molecule reaction technique, to model the high temperature gas phase reactions of alkali halide salt molecules. The reactions with Lewis acids such as SiFi, HF and CO2 yielded ion pair products which were quenched into inert matrices for spectroscopic study. Difficulties arising from lattice energy considerations in alkali halide salt reactions are minimized by the initial vaporization of the salt reactant. The reaction of such salt molecules with Lewis bases, including H2O and NH3, yielded complexes similar in nature to transition metal coordination complexes, with binding through the alkali metal cation to the base lone pair. 

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