Macrocycle vibrational bands

Physicochemical properties of so-called Fe " " and Fe° porphyrins have been reviewed by Reed who pointed out a possibility of partial migration of the reducing equivalents to the macrocycle. Vibrations of the porphyrin are expected to reflect the extent of delocalization of the reducing equivalents. The RR spectra of mono- and di-anions of Zn(TPP) and VO(EP) were reported by Ksenofontova et al. and Yamaguchi et al. and appreciable low frequency shifts of RR bands compared with those of neutral porphyrins were pointed out. Contrary to it, Srivatsa et al. did not find any difference between the RR spectra of Fe(TPP) and [Fe(TPP)] both in DMF (DMF dimethylformamide). 

One of the most relevant evidences of a relatively significant interaction between the macrocycle complex and the metal surface is the appearance of a vibrational band. This kind of metal-ligand bands is better observed in the Raman spectrum below 500cm . Bands corresponding to the adsorbate-substrate interaction were observed in azabipiridyl, phthalocyanines, naphthalocyanines and... 

The complex [Ni(2,3-Me2[14]-l,3-diene-l,4,8,lI-N4)] [ZnCU] is square planar and low-spin. The visible spectra show bands near 21.3 kK (characteristic of square planar nickel(II)), near 26.1 kK (due to the imine functions), and near 35.1 kK. The infrared spectra of all of the nickel complexes prepared show absorptions near 3195 and 1595 cm assignable to the N—H stretching vibration and to the symmetric imine vibration, respectively. A strong sharp band also occurs near 1210 cm and is characteristic of the a-diimine function. The NMR spectrum of the perchlorate complex in nitromethane shows a methyl singlet at 2.33 ppm. The ligand can be hydrogenated on nickel(II) with Raney nickel and hydrogen to produce the fully saturated macrocyclic complex [Ni(2,3-Me2[14]-ane-1,4,8,1 1-N4] ... 

In porphyrin chemistry M(TPP) is rather more frequently used than M(OEP) due to its easy preparation. Therefore, the vibrational analysis of M(TPP) is important. Appearance of the meso-phenyl modes in RR spectra was first pointed out by Burke et al. The IR and RR spectra of Ar-matrix isolated Co(TPP) and its deuterated derivatives were reported by Kozuka and Nakamoto There was an argument about the RR band around 1240 cm", which was assigned to the Cm-phenyl stretching mode for Fe(TPP) by Burke et al. but to a phenyl internal mode for Co(TPP) by Fuchsman et al. To determine the alternative, normal coordinate calculations were carried out for the A g species of Co(TPP) with the force field obtained for Ni(OEP) and the RR band in question was assigned to the phenyl internal mode. This suggests the presence of appreciable mixing of the Jt system of the macrocycle with that of the phenyl group at the meso positions. 

The luminescent emission of Ru (bpy)3 is also very useful for signalling anion binding. In the emission spectra of 37-40 both a blue shift (of up to 16 nm for 40) and an increase in intensity of the Amax of the MLCT emission band was observed on addition of dihydrogenphosphate. It has been proposed that the conformational flexibility of the receptors is decreased by complexation of the anion guest thus reducing the rate of non-radiative decay through vibrational and rotational relaxation. Similarly, macrocyclic complexes 41-44 and 77-79 were also found to sense chloride by luminescence enhancement. 

In other words, the Q bands are forbidden and simply shouldn t exist. The fact that they do is because of molecular vibrations within the porphyrin macrocycle. These have the effect of marginally lifting the degeneracy of bj and b2 so that the difference in intensities represented by Qy and is no longer equal to zero, i.e. the Q bands become weakly allowed. Their weakness allows them to show vibrational fine structure. In the case of a porphyrin dication or metal complex, where the x and y directions for the components of the transition dipoles are equivalent, this gives rise to two Q bands. For porphyrin free bases, where the x and y directions are perpendicular to each other, each component has two associated Q bands, so the total number is four. 

This chapter has been organized by considering several aspects. An introduction concerning the relevance of the electronic properties and applications of the azamacrocycles related to surface phenomena as well as the general aspects and characteristics of the vibrational techniques, instruments and surfaces normally used in the study of the adsorbate-surface interaction. The vibrational enhanced Raman and infrared surface spectroscopies, along with the reflection-absorption infrared spectroscopy to the study of the interaction of several azamacrocycles with different metal surfaces are discussed. The analysis of the most recent publications concerning data on bands assignment, normal coordinate analysis, surface-enhanced Raman and infrared spectroscopies, reflection-absorption infrared spectra and theoretical calculations on models of the adsorbate-substrate interaction is performed. Finally, new trends about modified metal surfaces for surface-enhanced vibrational studies of new macrocycles and different molecular systems are commented. 

Ard " and Gladkov and Solovyov propose, from normal coordinate calculations performed for the copper porphin complex, that bands near 368, 234 and 206 cm contain important contributions of the vCuN mode. From a vibrational study on the non-macrocycle phenantroline copper complexes it has been proposed the vCuN modes near 410 and 288 cm In bipyridine complexes of Cu(II), the vCuN mode is proposed at 297cm " a similar assignment is proposed in bipyrimidine complexes. ... 

Macrocycle deformations are observed between 640 and 120 cm in NPcVO and in the range 510-350 cm in Pc VO the highest frequencies correspond to the ring deformations of benzene and pyrrole, while the lowest are macrocycle ring deformations. Bands at 570 and 457cm in PcVO and the band at 537 cm of NPcVO are characteristic of each macrocycle. Bands at 372, 308 and 235 cm observed only in the vanadyl compounds correspond to VO-N vibrations. Other bands in this region are mainly due to macrocycle ring out of plane deformations. 

The complex formation is verified in this spectral region by the appearance of several bands, see Figure 14.15. Bands about 430, 350 and 325 cm" - only observed in the complexes are ascribed to metal sensitive vibrations they are macrocycle ring deformations. The band at about 291 cm in the spectrum of... 

From the resonance Raman spectra of phthalocyanine monolayers on different metals and a normal mode analysis, Palys et al7, conclude that the Raman band at 678 cm" is described by an in-plane macrocycle mode coupled to an out of plane CH deformation. Moreover they conclude that the phthalocyanine molecule is bonded via nitrogen atoms to a glassy carbon surface, and through the metal ion when the molecule interacts with a gold surface. On this basis it was proposed that this band is due to an in and out of plane concerted tt electronic system motion, corresponding to the breathing mode coupled to the out of plane CH vibration (pCH). This assignment explains the presence of this band in the... 

The relative intensity enhancement of the out of plane bands suggests that the corresponding vibrations are mainly parallel to the normal of the incident radiation. Thus, the macrocycle complexes have a preferential face-on orientation... 

These excitation wavelengths span the Qy absorption bands of P, the accessory BChls, and the BPhs. The RR spectra obtained at all excitation wavelengths exhibit a number of bands. The bands in the 1400-1630-cm region are due to in-plane skeletal modes of the macrocycles whereas those above 1630 cm are due to carbonyl stretching vibrations of various substituent groups [1-3]. The frequencies of these modes are quite sensitive to the structure of the macrocycles in the protein matrix [1-3,10]. These structure-sensitive bands will be the focus of the discussion. 

The second conclnsion of this work is that calculated vibrational spectra and the Fukui reactivity indices give valuable information on the attribution of the experimental bands and understanding of local reactivity of macrocycle ligands as weU as the evolution of reactions involving several steps. 

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