Spectral and Electronic Properties

The infrared spectra revealed the dominance of the 2-oxo (153) and 5-0X0 (157) structures (amide or lactam tautomers) over the 2-hydroxy (154) and the 5-hydroxy (192) structures (imidic acid or lactim tautomers) 

The infrared spectrum of l,5-diamino-l,2,4-triazolo[l,5-c]quinazolinium bromide (75) showed two intense absorptions near 1700 cm . These absorptions were interpreted, on the basis of deuteration experiments, to be due to V C=N coupled with 8 NH2 and other ring modes [79JCS(P2)1708]. 

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The mixed-ligand complexes RNiX3B (B = PPh3, py and substituted pyridines) have been prepared in general by the reaction of RX and NiX2 in the presence of the Lewis base B in hot butanol.2223 "33,2234,2238,2239 2244 These complexes have a distorted tetrahedral structure2238,2239 and their spectral and electronic properties have been investigated in detail.2245... 

Liptak MD, Brunold TC. (2006) Spectroscopic and computational studies of Col-l-cobalamin spectral and electronic properties of the superreduced B12 cofactor. J Am Chem Soc 128 9144-9156. 

The chemical and electronic properties of elements at the interfaces between very thin films and bulk substrates are important in several technological areas, particularly microelectronics, sensors, catalysis, metal protection, and solar cells. To study conditions at an interface, depth profiling by ion bombardment is inadvisable, because both composition and chemical state can be altered by interaction with energetic positive ions. The normal procedure is, therefore, to start with a clean or other well-characterized substrate and deposit the thin film on to it slowly at a chosen temperature while XPS is used to monitor the composition and chemical state by recording selected characteristic spectra. The procedure continues until no further spectral changes occur, as a function of film thickness, of time elapsed since deposition, or of changes in substrate temperature. 

Crystal-field theory (CFT) was constructed as the first theoretical model to account for these spectral differences. Its central idea is simple in the extreme. In free atoms and ions, all electrons, but for our interests particularly the outer or non-core electrons, are subject to three main energetic constraints a) they possess kinetic energy, b) they are attracted to the nucleus and c) they repel one another. (We shall put that a little more exactly, and symbolically, later). Within the environment of other ions, as for example within the lattice of a crystal, those electrons are expected to be subject also to one further constraint. Namely, they will be affected by the non-spherical electric field established by the surrounding ions. That electric field was called the crystalline field , but we now simply call it the crystal field . Since we are almost exclusively concerned with the spectral and other properties of positively charged transition-metal ions surrounded by anions of the lattice, the effect of the crystal field is to repel the electrons. 

A few thioether-ligated copper(II) complexes have been reported, however (cf. Section 6.6.3.1.2) (417) (essentially square planar), (418) (two crystalline forms one TBP and other SP),361 (419) (SP),362 (420) (SP),362 (421) (TBP),362 (422) (SP),363 (423) (SP),363 (424) (two independent complexes SP and octahedral),364 (425) (TBP).364 In the complexes (420) and (421), EPR spectra revealed that the interaction between the unpaired electron and the nuclear spin of the halogen atom is dependent on the character of the ligand present. For (424) and (425), spectral and redox properties were also investigated. Rorabacher et al.365 nicely demonstrated the influence of coordination geometry upon CV/Cu1 redox potentials, and reported structures of complexes (426) and (427). Both the Cu1 (Section 6.6.4.5.1) and Cu11 complexes have virtual C3v symmetry. 

In this section we outline briefly the spectral and magnetic properties of complexes of the metals of Table 5. These are the properties that enable the stereo-chemical and electronic structures of metal complexes to be determined in solution and, hence in a biological environment. A study of these properties will be necessary to understand the nature of the interaction of the anti-tumour compounds with biological systems. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

The preparation of these materials led to a review by Ashe (78ACR153) of the spectral and chemical properties of the Group V heterobenzenes. He concluded that arsenin, antimonin and bismin were aromatic in character with the degree of aromaticity decreasing with increasing size of the heteroatom. This was supported by NMR, electron diffraction, microwave and UV photoelectron spectral studies and is discussed below. 

Interest in the interpretation of the spectral and magnetic properties of oxo-vanadium(iv) complexes has grown as it has become apparent that the general assumption of overall C4 symmetry for these complexes is unjustified. Bis-(2-methyl-8-quinolato)oxovanadium(iv), VO(quin)2,395 and bis(tetramethylurea)dichloro-oxo-vanadium(iv), VO(tmu)2Cl2,396 for example, have been found to be five-co-ordinate with a trigonal-bipyramidal co-ordination polyhedron about the vanadium atom. A crystal-field model has been developed which gives a good account of the electronic and e.p.r. spectra of VO(quin)2. 

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