Matrix cocondensed

By use of quantitative, metal-atom, matrix-cocondensation techniques and the kinetic analysis previously discussed, the dimeric spe-... 

A report by Ozin et al. in 1977 describes the formation of Ti(CO)6 via matrix cocondensation techniques (11). This green complex, while not isolated, was characterized by its infrared and ultraviolet-visible spectra. In a pure CO matrix, a color change from green to reddish-brown was observed on warming from 10 K to about 40-50 K. The infrared spectrum of the reddish-brown material showed no evidence for coordinated CO, thus suggesting the extreme thermal instability of Ti(CO)6. 

G.A. Ozin, University of Toronto In our Cr/CO matrix cocondensation experiments (Angew. Chem., Int. Ed. Eng. 1975, 14, 292), we reported evidence for the facile formation of a binuclear chromium carbonyl complex Cr2(CO)i0 or Cr2 (CCOi x which could be described as square pyramidal Cr(CO)5 weakly interacting with either a Cr(CO)5 or Cr(CO)6 moiety in the vacant (sixth) site. As a result, the infrared spectrum of this "weakly-coupled" binuclear species closely resembled that of the mononuclear fragment Cr(CO)5. I would like to ask you, whether or not you have any evidence for the existence of such a binuclear species in your Cr(CO)6 /Xe cryogenic solutions following various photolysis treatments. 

A number of unstable and transient species have been synthesized via matrix cocondensation reactions, and their structure and bonding have been studied by vibrational spectroscopy. The principle of the method is to cocondense two solute vapors (atom, salt, or molecule) diluted by an inert gas on an IR window (IR spectroscopy) or a metal plate (Raman spectroscopy) that is cooled to low temperature by a cryocooler. Solid compounds can be vaporized by conventional heating (Knudsen cell), laser ablation, or other techniques, and mixed with inert gases at proper ratios [128]. In general, the spectra of the cocondensation products thus obtained exhibit many peaks as a result of the mixed species produced. In order to make band assignments, the effects of changing the temperature, concentration (dilution ratios), and isotope substitution on the spectra must be studied. In some cases, theoretical calculations (Sec. 1.24) must be carried out to determine the structure and to make band assignments. Vibrational frequencies of many molecules and ions obtained by matrix cocondensation reactions are listed in Chapter 2. 

Matrix cocondensation reactions are classified into the following five types ... 

Salt-Molecule Reaction. Tevault and Nakamoto [131] carried out matrix cocondensation reactions of metal salts such as PbF2 with L(CO, NO and N2) in Ar, and confirmed the formation of PbF2-L adducts by observing the shifts of IR bands of both components. These spectra are shown in Fig. 3.67 (of Sec. 3.18.6). 

Metal dioxides produced by sputtering techniques [371] in inert gas matrices take linear or bent O—M—O structures. Metal dinitrides produced by the same technique also take linear N—M—N (M = U [372] and Pu [373]) or bent N—M—N (M = Th [374]) structures. These structures are markedly different from those of molecular oxygen and nitrogen complexes of various metals produced by the conventional matrix cocondensation technique (Chapter 3 in Part B). 

Matrix cocondensation reactions of alkali halide molecules (M X ) with H2O diluted in Ar produce pyramidal [MOH2J ions that exhibit the v(OH2) and 5(OH2) in the 3300-3100 and 700-400cm regions, respectively [665]. These ions may serve as simple models of aquo complexes. 

Deeply colored polymers upon warming no compounds containing Si and N are formed Matrix cocondensation polymers Hexafluorodisiloxane and unidentified chain and cyclic fluorinated siloxanes... 

V(CO)e generated by cocondensing presynthesized V(CO)6 with N2 at 10 K has been observed (44, 45). As suggested in a metal-atom study (125), the results indicated that a static, Jahn-Teller distortion is present. Matrix MCD also proved useful in confirming the predicted paramagnetism of Fe(CO)4 (45) (produced by photolysis of Fe(CO)5). In addition, matrix MCD was used to detect such paramagnetic species as MnOaCU in the presence of MnOsCl (45). 

A number of investigations of the copper-group oxides and dioxygen complexes have been reported. The electronic spectra of CuO, AgO, and AuO were recorded in rare-gas matrices (9), and it was found that the three oxides could be formed effectively by cocondensation of the metal atoms with a dilute, oxygen matrix, followed by near-ultraviolet excitation. The effective wavelengths for CuO or AgO formation were X > 300 nm and for AuO was X > 200 nm. In addition, the laser fluorescence spectrum of CuO in solid Ar has been recorded (97). 

The vapor above molten Cu, Ag or Au contains predominantly atoms, but dimers are also present to ca. 0.1%. Study of these in the vapor is impeded by the high concentration of atomic metal. When these vaporized metals are cocondensed with an inert substanee, sueh as Ar, CH4, Kr, Xe at 10-12 K, a solid containing metal atoms in the inert matrix is obtained. As the proportion of metal to inert substance is... 

When Ag vapor is cocondensed with CO at 10-12 K the compound Ag(CO), is formed as separate molecules in a CO matrix. When this is warmed to 30-37 K for about 1 h dimerization takes place ... 

Huber et al. 189) have investigated cocondensation (4.2—10 °K) reactions between Ni, Pd and Pt and molecular oxygen in pure O2 and Oj/Ar matrices. These reactions were studied by matrix isolation infra-red spectroscopy, including isotopic and diffusion controlled warm-up studies. They established that both M(02) and (0j)M(02) species were present. The 0-0 bond order suggested significant back-bonding, and this led them to reject the monodentate stmcture. Fig. 8 (b). 

The stability of molecules depends in the first place on limiting conditions. Small, mostly triatomic silylenes and germylenes have been synthesized successfully at high temperatures and low pressures, 718). Their reactions can be studied by warming up the frozen cocondensates with an appropriate reactant, whereas their structures are determined by matrix techniques 17,18). In addition, reactions in the gas phase or electron diffraction are valuable tools for elucidating the structures and properties of these compounds. In synthetic chemistry, adequate precursors are often used to produce intermediates which spontaneously react with trapping reagents 7). The analysis of the products is then utilized to define more accurately the structure of the intermediate. 

FIG. 1. Schematic picture of the cocondensation-high-vacuum system for the generation of gaseous MX species and their trapping in a matrix of an organic solvent. 

The application of matrix isolation to organometallic chemistry has been extensively described elsewhere (4,5,6,7). Two methods have generally been employed. In the first, based on G.C. Pimentel s original development, the solid matrix environment is a frozen noble gas - usually Ar - at 10-20K and the unstable fragment is generated either by photolysis of a parent molecule already trapped in the matrix, or by cocondensation from the gas phase. In the... 

The constants of equations 6.16 and 6.17 are identical, on the basis of the principle of equal reactivity of cocondensing functional groups. Adopting Temkin s model for fused salts, and thus assuming that molar fractions represent activities over the appropriate matrix, we obtain... 

Cocondensation of a precursor with a reagent with which it will react in the matrix (usually during the condensation process). 

However, there are some exceptions. One of them is the possibility of (photo)-protonation or -deprotonation. If a matrix is doped with sufficient amounts of a proton donor or acceptor, chances are that the substrate will give up or accept a proton already on cocondensation or on subsequent photoexcitation. In fact, the higher noble gases (Ar, Kr, Xe) are themselves good proton acceptors, forming (NG H)+ complexes that can be identified by their characteristic IR vibrations. This feature allows occasionally to observe radicals formed by deprotonation of radical cations formed in noble gas matrices, for example, benzyl radical from ionized toluene. However, we know of no examples where a carbanion was formed by deprotonation in matrices. 

The ESR spectra of all zerovalent derivatives are consistent with the paramagnetism expected for 17-electron d5 compounds with one unpaired electron ([Nb(7/6-C6H5Me)2] (g) = 1.992, (A) = 45.9 G). Cocondensation of Nb atoms with N2 in an Ar matrix gave... 

To gain more insight into silver-dioxygen species, a matrix isolation study involving cocondensation of Ag atoms with 1602 and 1802 was initiated. Two products were obtained,... 

Disilene and its isomer silylsilylene were neither available by standard vacuum flash pyrolysis of precursors 59-63, nor by the more elaborate method of pulsed flash pyrolysis of 60-63, a pulsed discharge in mixtures of argon and mono- and disilane74 or by the matrix photolysis of educts 59-66 using various light sources (Hg lamps, excimer laser)69,70,72, the microwave discharge in disilane 66 or the cocondensation of silicon atoms with SiFLt. 

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