Transition metal complexes stretching frequencies

Pyridine 1-oxide, like pyridine, can act as a ligand in transition metal complexes, but unfortunately good stability constants are not known. However, Shupack and Orchin have found that the C===C stretching frequency of the ethylene ligand in trans-ethylene pyridine 1-oxide dichloroplatinum(II) varies linearly with the pA and hence with the C7-value (ct+ or a, respectively) of substituents in the pyridine oxide. The data for the above reaction series are included in Table V. 

Si—M Stretching Frequencies for Silicon-Transition Metal Complexes... 

The use of infra-red or ultraviolet spectroscopy to examine the molecular groups present in a chemical compound is familiar to any chemist. One of the main uses of this technique is to apply a range of electromagnetic frequencies to a sample and thus identify the frequency at which a process occurs. This can be characteristic of, say, the stretch of a carbonyl group or an electronic transition in a metal complex. The frequency, wavelength or wavenumber at which an absorption occurs is of most interest to an analytical chemist. In order to use this information quantitatively, for example to establish the concentration of a molecule present in a sample, the Beer-Lambert law is used ... 

Compounds of transition metal complexes possessing a nonbonding electron pair with boranes (BX3) can be regarded classically as boron complexes with a transition metal ligand. In a broader sense, however, boranes can be classified as acceptor ligands.154,155 Thus, coordination of a borane results in a decrease of the electron density on the metal atom. In the case of carbonyl complexes this effect is reflected in the increase, by 20-100 cm-1, of the CO stretching frequency.154-156 It follows from the foregoing that stable coordination of boranes is... 

The carbon dioxide molecule exhibits several functionalities through which it may interact with transition metal complexes and/or substrates. The dominant characteristic of C02 is the Lewis acidity of the central carbon atom, and the principle mode of reaction of C02 in its main group chemistry is as an electrophile at the carbon center. Consequently, metal complex formation may be anticipated with basic, electron-rich, low-valent metal centers. An analogous interaction is found in the reaction of the Lewis acid BF3 with the low-valent metal complex IrCl(CO)(PPh3)2 (114). These species form a 1 1 adduct in solution evidence for an Ir-BF3 donor-acceptor bond includes a change in the carbonyl stretching frequency from 1968 to 2067 cm-1. 

The CS2 complexes are prepared by the reaction of CS2 with transition metal complexes. The ligand in the M-rf-CSz and M-tj CSj coordination modes acts as a good 77-acceptor and a poor cr-donor as shown by the lower CS stretching frequencies found in the complexes relative to that of free CS2. 

In Table VII are recorded mean values for in a number of ethylene-metal carbonyl complexes and parent metal carbonyls as well as values for the double-bond infrared stretching frequency rc c the magnetic shielding parameter t for ethylene in those transition metal complexes for which data are available. Although with the metal carbonyl complexes, differences of geometry, oxidation state, etc., do not permit a correlation to be drawn between the absolute values of rco and for the various complexes, it is quite apparent from the tabulated data for the Mo, Mn, and Fe complexes that for a given metal. 

Haymore and Ibers (62) have developed a series of corrections to the observed i no stretching frequencies that take into account the position of the metal in the periodic table, the charge on the complex, the metal s coordination number, and the other ligands present. The resulting corrected i no are more successful in predicting the nitrosyl geometry in transition metal complexes. 

Fig. 11 B-H stretching frequencies of first-row transition metal complexes which have been characterised by X-ray diffraction. Complexes are presented from the left to the right of the periodic table, and classified according to coordination mode, first rj1, then r 2, followed by combined complexes with x 2 and r]3 BH4- and finally r]3 complexes. The highest frequency is represented as a black rhomboid, the second as a grey square, the third as a white triangle and so on...

A general discussion of the infrared spectra of transition metal complexes has been published (23). Although correlations of CO bending modes (24) and of band intensities (25,26) have appeared and vibrations of other ligands are often noted, the number of CO stretching modes and their exact frequencies are the data most frequently cited for metal carbonyl com-... 

For transition metal complexes, the metal-halogen stretching frequency has been found to be dependent on the trans influence of the ligand in the trans position (see page 292). 

The first examples of such studies that are relevant to solar energy conversion are those of transition metal complexes functioning as light harvesters and catalysts. For example, the ground state metal to nitrogen stretching frequency... 

The extent of metal-P coordination is reflected in the Raman C=C stretch frequency [72]. Uncoordinated dppa has a lower v(C=C) of 2,097 cm than most disubstituted acetylenes (v = 2,190-2,260 cm ) as the conjugated phosphorus lone pair causes 7i-electron depletion from the triple bond (Fig. 2.18). Transition metal complexation suppresses this effect. The magnitude of Av(C=C), i.e., v(complexed dppa) — v(free dppa), then reflects the degree of P M a-bonding. Electron depletion of the triple bond has been inadvertently attributed to the contribution of P(d,7i) orbitals, as well as M P 7r-bonding to the increase in Av(C=C) [72]. 

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