Salicylidene Aniline Research Articles

Spectroscopic investigation of some salicylidene hydrazone derivatives and their chelates with Co(II), Ni(II) and Cu(II)

Spectroscopic studies on arylhydrazone derivatives are rather few, despite the fact that these compounds are rather interesting che- lating agents. For sake of comparison with Schiff bases, the spectra of some hydrazones are discussed I4. It was shown that the two com¬pounds showed strong H-bonding, which is stronger in hydrazones compared to Schi ff bases (4). Chelate formation with salicylidene aniline through C = N coor¬dination is confirmed from the analysis of the ir-spectra based on the shift of the C=N band to lower wavenumbers (5). On the contrary che¬late formation with salicylidene phenyl hydrazone leads to a shift of the C =N band to higher wavenumbers, which was explained on the hasis of electron feed back from the metal ion to the C =N linkage (6). As a matter of fact, the transfer of an electron from the metal ion to

Bis(indenyl)titanium(IV) and zirconium(IV) complexes of monofunctional bidentate salicylidimines

Dichlorobis(indenyl)-titanium(IV) and -zirconium(IV), (C 9H 7) 2TiCl 2 and (C 9H 7) 2ZrCl 2, react with bidentate Schiff bases such as salicylidene aniline, salicylidene- o-toluidine, salicylidene- m-toluidine and salicylidene- p-toluidine in a 1:1 molar ratio in refluxing tetrahydrofuran in the presence of triethylamine to yield complexes of the type (C 9H 7) 2Ti(SB)Cl and (C 9H 7) 2Zr(SB)Cl, respectively where SB is the anion of the corresponding Schiff base, SBH. The new derivatives have been characterised on the basis of their elemental analyses, conductance measurements and spectral (IR, 1H NMR and electronic) studies.

High pressure optical studies of crystalline anils and related compounds

High pressure optical studies have been made on a series of crystalline therochromic and photochromic anils and model compounds. Measurements include absorption and emission peak locations and the integrated intensities of various absorption peaks including the uv peak and visible peaks introduced thermally or by irradiation at various temperatures and pressures. Emission yields were also obtained. For the thermochromic compounds there was a large increase in the equilibrium yield of the thermally induced peak with pressure (piezochromism), corresponding to a volume decrease of ∼1.2 cc/mole for 5-bromosalicylidene aniline (5BrSA). The emission peak shifts to lower energy and decreases in intensity primarily because of increased rate of the radiationless conversion. For salicylidene aniline and related photochromic crystals the rate of photochromic conversion varied with both pressure and temperature in a manner which depends on the size of the energy barriers to the forward and reverse processes. The emission yield increases with pressure at low pressure, goes through a maximum, and decreases at high pressure. At low pressure the dominant feature is increase in occupation of the emitting state while at high pressure the increased rate of the radiationless process governs. For 2- (O-hydroxyphenyl) benzoxazole (OHBO) (see Fig. 1), where a keto–enol rearrangement is most probable, the changes in absorption and emission intensity can be related to the same diagram used for the anils. This diagram also describes the behavior of benzilidene aniline (BA), where only a cis–trans isomerization is possible.

Photochromism of Salicylidene Aniline

Photochromic properties of two crystalline forms of salicylidene aniline have been investigated, emphasizing properties not previously evaluated. A broad band with maximum absorbance at 480 mmu is induced by near uv radiation; 380 mmu is most effective. Occurring spontaneously, the reverse change is accelerated by visible radiation; 480 mmu is most effective. The two crystalline forms require similar energy for inducing the 480-mmu band, but differ markedly in energy for the reverse change and in the kinetics of spontaneous fading. For thin films, maximum absorbance change divided by thickness is about 0.5mu(-1). The compound resists fatigue excellently when cycled by radiation most effective for photochromic changes.

Photochromism. I. The Spectroscopy and Energy Levels of Salicylideneaniline

As a prerequisite to understanding the photochemistry of salicylideneaniline, its energy levels and their characteristics are deduced from absorption and emission spectra, and by comparison with related molecules. Theoretical calculations are used to help to establish relations between stilbene, benzylideneaniline, azobenzene, and salicylideneaniline (SA). It is concluded that all the ππ* bands observed in SA below 6 eV have analogs in the allowed or forbidden transitions of stilbene. From a study of solvent effects, it is concluded that the internal hydrogen bond of SA causes large changes of band intensity, but relatively small energy changes. The luminescence of SA appears to come from the second triplet rather than the first. This could be understood if the two lowest triplets have quite different geometries. The problem of the triplets is discussed further in the second part of this series.

The CN stretching frequency in the infrared spectra of Schiff's base complexes—I. Copper complexes of salicylidene anilines

The CN stretching frequency in seventeen substituted salicylidene aniline—copper (II) complexes is assigned both in the solid state and in solution. In Nujol mulls, the CN stretching frequency is found at 1603–1616 cm −1, while in methylene chloride solution, the band is shifted slightly to 1602–1612 cm −1. In the copper (II) complexes, the phenolic CO appears in the region 1310–1330 cm −1 as compared to 1265–1288 cm −1 in the free anils.

Piezoelectricity in Salicylidene Aniline Crystals

The resonance frequencies of various single crystals of salicylidene aniline were measured for different modes of vibration, and the velocities of sound waves in these materials were deduced. Values are given for the electric equivalent circuit parameters and elastic constants in such crystals.