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During the last 50 years a vast number of structural studies on Schiff bases derived from hydroxyaryl aldehydes and their coordination compounds have been undertaken. In this review we present a systematic and brief overview of the most important discoveries and achievements accomplished in this field. The occurrence of Schiff bases (and their complexes) derived from nine most commonly used hydroxyaryl aldehydes in the Cambridge Structural Database (CSD) has been investigated. Keto-enol tautomerism and intramolecular hydrogen bonding in salicylaldimines and naphthaldimines is discussed, with a comment of the most common errors in determining the correct tautomeric form. Also, the interrelationship of crystal packing and the substituents on the Schiff base is studied. Finally, we give a short overview of conformational differences between free Schiff bases and Schiff bases bonded to metal ions as well as some structural characteristics of Schiff base metal complexes.

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5121 (23) Clegg, H. P.; Rowlinson, J. S. Faraday SOC. Tram. 1955,51,1333. (24) Gugnoni, R. J.; Eldrige, J. w.; Okay, V. C.; Lee, T. J. AIChE J. 1974, (25) Aftienjew, J.; Zawisza, A. J. Chem. Thermodyn. 1977, 9, 153. (26) Haselden, G. G.; Newitt, D. M.; Shah, S. M. Proc. R. SOC. A 1951, (19) Prausnitz, J. M.; Lichtenthaler, R. N.; Gomes de Azevedo, E.Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times are used to investigate the guest and host molecular dynamics of solid 1 ,4-di-terr-butylbenzene-d4 (DTBB-d4), l,4-di-tert-butylbenzne-dl* (DTBB-d18), the thiourea/ 1 ,4-di-tert-butylbenzene-d4 inclusion compound (TUIDTBB-d4), the thiourea/ 1,4-di-tert-butylbenzene-d~ inclusion compound (TU/DTBB-dz2), the thiourea-d4/ 1,4-di-tert-butylbenzene inclusion compound (TU-d4/DTBB), and thiourea-d4 (TU-d4). X-ray crystallographic studies of TU/DTBB-d4 have been carried out at 291 K. In solid DTBB the phenyl ring is essentially static whereas the rert-butyl groups are undergoing rapid reorientation of both methyl and rert-butyl groups.Attempts to analyze the ' H spectra and Tl data for DTBB-dls suggest that the dynamics of the methyl and tert-butyl groups are nearly equivalent, and as a result, a satisfactory analysis, yielding methyl and tert-butyl rotational activation energies, was not possible. X-ray diffraction results for TU/DTBB-d4 suggest that, at 291 K, the phenyl ring is occupying three nearly equivalent sites. The ZH NMR line shapes between 186 and 392 K were interpreted using a model in which the phenyl ring is rapidly flipping between three positions, with one position less favored. At 296 and 186 K the populations are 0.81:1.00.1.00 and 0.201.00.1 .OO, respectively. Relaxation times obtained between 1 1 1 and 322 K show no mini", supporting the assumption of very rapid phenyl ring reorientation. For TU/DTBB-d2z a high-temperature T1 minimum is well-defined, and a second minimum, corresponding to tert-butyl group rotation, is reached at the lowest attainable temperatures. Lineshape simulations of the spectrum at 77 K yield methyl and tert-butyl group rotational rates of 1.0 X lo3 and 2.0 X 106 s-l, respectively. Analysis of the higher temperature spectra (109-172 K) and T1 data (167-300 K) yield methyl rotation activation energies of 12.7 and 12.3 kJ/mol, respectively. Deuterium line-shape studies of the thiourea dynamics in TU-d4 and TU-d4/DTBB yield activation energies for 180' flips about the C-S bond of 47 and 46 kJ/mol, respectively.Starting from the PY-like integral equation of RISM-1 type and using the Kirkwood-Buff theory, we evaluated the differences in the partial molar volumes of solute V : of cis and trans isomers. The system investigated consists of a tetratomic A-B-B-A fused hard sphere and a single hard sphere both of which are considered as solvent or solute. To compare the evaluated values with the actual values, the VTs were determined for cis-and trans-decahydronaphthalene dissolved in such solvents as carbon tetrachloride, hexane, and benzene, etc., as well as ...

Complexation of alkali-metal cations with calix[4]arene secondary-amide derivative, 5,11,17,23-tetra(tert-butyl)-25,26,27,28-tetra(N-hexylcarbamoylmethoxy)calix[4]arene (L), in benzonitrile (PhCN) and methanol (MeOH) was studied by means of microcalorimetry, UV and NMR spectroscopies, and in the solid state by X-ray crystallography. The inclusion of solvent molecules (including acetonitrile, MeCN) in the calixarene hydrophobic cavity was also investigated. The classical molecular dynamics (MD) simulations of the systems studied were carried out. By combining the results obtained using the mentioned experimental and computational techniques, an attempt was made to get an as detailed insight into the complexation reactions as possible. The thermodynamic parameters, that is, equilibrium constants, reaction Gibbs energies, enthalpies, and entropies, of the investigated processes were determined and discussed. The stability constants of the 1:1 (metal:ligand) complexes measured by different methods were in very good agreement. Solution Gibbs energies of the ligand and its complexes with Na(+) and K(+) in methanol and acetonitrile were determined. It was established that from the thermodynamic point of view, apart from cation solvation, the most important reason for the huge difference in the stability of these complexes in the two solvents lay in the fact that the transfer of complex species from MeOH to MeCN was quite favorable. That could be at least partly explained by a more exergonic inclusion of the solvent molecule in the complexed calixarene cone in MeCN as compared to MeOH, which was supported by MD simulations. Molecular and crystal structures of the lithium cation complex of L with the benzonitrile molecule bound in the hydrophobic calixarene cavity were determined by single-crystal X-ray diffraction. As far as we are aware, for the first time the alkali-metal cation was found to be coordinated by the solvent nitrile group in a calixarene adduct. According to the results of MD simulations, the probability of such orientation of the benzonitrile molecule included in the ligand cone was by far the largest in the case of LiL(+) complex. Because of the favorable PhCN-Li(+) interaction, L was proven to have the highest affinity toward the lithium ion in benzonitrile, which was not the case in the other solvents examined (in acetonitrile, sodium complex was the most stable, whereas in methanol, complexation of lithium was not even observed). That could serve as a remarkable example showing the importance of specific solvent-solute interactions in determining the equilibrium in solution.