D. Ajo

Heteropolymetallic complexes of 1,1′-Bis(diphenylphosphino)ferrocene (dppf). III. Comparative physicochemical properties of (dppf)MCl2 (M = Co, Ni, Pd, Pt, Zn, Cd, Hg)

Abstract 1,1′-Bis(diphenylphosphino)ferrocene (dppf) metal dichlorides (metal = Co, Ni, Pd, Pt, Zn, Cd, and Hg) are examined as a class of related complexes. Their electronic, infrared, mass, 31P NMR, and Mossbauer spectra as well as the HeI and HeII photoelectron spectra of dppf are presented and discussed. Cyclovoltammetric tests in dichloroethane indicate that the ferrocene moiety undergoes a strong stabilization towards oxidation, and the ferricinium derivatives are well characterized in the case of Pd(II) and Pt(II). Differential scanning calorimetric tests reveal that all the complexes are thermally very stable, particularly the Zn(II) and Cd(II) derivatives, which melt without previous decomposition in the temperature range 300–305 °C. Cyclovoltammetric and field desorption mass spectral tests reveal that the [(dppf)MCl2]+ species are stable only when M = Pd, Pt.

Crystal structure and conformational flexibility of 2-(acetylamino)prop-2-enoic acid (N-acetyldehydroalanine)

The molecular structure of N-acetyldehydroalanine (2-acetylaminoprop-2-enoic acid) has been determined from three-dimensional X-ray data. C5H7NO3 is monoclinic, space group P21/n, with Z= 4 in a cell of dimensions a= 14.904(7), b= 10.162(6), c= 3.943(3)A, β= 91.7(1)°. The structure was solved by direct methods and refined by full-matrix least-squares to R 0.060 for 1 350 observed reflections. The molecules exhibit a fully planar conformation and are linked by OH ⋯ O hydrogen bonds to form one-dimensional chains. The conformational flexibility is discussed on the basis of ab initio and empirical calculations.

Nature of the metal-meal bond in triangulo -Ru3(CO)12 from UVphotoelectro spectroscopy and quantum mechanical calculations

Abstract The HOMO nature of RuRu bonds in triangulo-Ru 3 (CO) 12 has been evidentiated by He(I) photo-electron spectroscopy and CNDO calculations. The bonding features of the three membered ring are compared to Walshs picture of the ‘isoelectronic’ ring of cyclopropane. Both 4d and 5s5p orbitals are significantly involved in the RuRu bonds.

Torsional potential barriers in conjugated molecules: unsaturated N-substituted amides

Abstract A theoretical study on torsional potential barriers in diformamide and N -vinylformamide is described. The mutual influence between π bonds with respect to the conformational rigidity is discussed on the basis of ab initio and PEM (Partition of Energy Method) calculations. The introduction of unidimensional torsional potentials in the PEM scheme provided good agreement with the ab initio results.

Electronic structure of xanthine and its biological methyl derivatives by u.v. photoelectron spectroscopy

Abstract He(I) excited photoelectron spectra of xanthine, theophylline, theobromine and caffeine are presented and discussed. The spectra are unequivocally assigned using CNDO calculations and comparison arguments to some related molecules. Methyl substitution effects proved to be a powerful tool for reliable assignments of the spectra.

Conformational analysis of malonic acid and its derivatives: ab initio, CNDO/2 and empirical calculations

Abstract Theoretical conformational analysis of malonic acid and α-substituted derivatives has been performed by ab initio, CNDO/2 and PEM (Partition of the Energy Method) techniques. For malonic acid, a high conformational flexibility, not substantially modified by the α-substitution, is predicted. Owing to the high flexibility, intermolecular interactions play an important role in determining the crystal state conformations of these compounds. The agreement between X-ray data and theoretical results is discussed.

Electronic structure of μ-methylene-bis-[dicarbonyl(η5-cyclopentadienyl)manganese] by UV photoelectron spectroscopy

Abstract The results of an investigation on μ-CH 2 -[(η 5 C 5 H 5 )Mn(CO) 2 ] 2 by means of UV vapour-phase photoelectron spectroscopy and CNDO quantum mechanical calculations are reported and discussed. Three distinct bands are assigned to ionizations from the MOs (27a, 26b, 22a) mainly contributing to the three membered ring bonding. In particular, 27a HOMO and 26b MO mainly represent MnMn and MnCH 2 Mn bonding interactions. On the contrary, 22a MO, reminiscent of the Walsh-type totally symmetric MO, is mainly localized on the methylene carbon atom.

The alkyne-cluster interaction in a ruthenium “butterfly” acetylenic carbonyl complex. An UV-PES and theoretical study

Abstract The electronic structure of “butterfly” Ru4(CO)12(RC2R) cluster complexes is discussed on the basis of He(I) PE spectroscopy and CNDO quantum mechanical calculations. The theoretical results contribute to the discussion of the PE data and provide novel insights into the alkyne-cluster bonding scheme. The most interesting feature emerging from this study is the different roles of the “hinge” and “wing” ruthenium atoms: the former are involved in both donation and back-donation with the alkyne, whereas the latter are primarily involved in the donation only. This gives rise to a particularly stable arrangement, because the two highly polarizable Ru3 triangles provide a mechanism for balancing the charges.

Electronic structure of imides by UV photoelectron spectroscopy and INDO/S calculations: hydantoin and urazole

He(I) excited photoelectron spectra of hydantoin, 1-methylhydantoin and urazole are presented and discussed. The spectra are assigned by comparison with the spectrum of succinimide and by INDO/S calculations. The electronic structure of the imido group of succinimide is not substantially perturbed by the replacement of one or two CH2 groups by NH groups. The HOMO is mainly localized on the additional nitrogen atoms in both the title compounds.

Investigation of the electronic structure of trans-cinnamic acid and cinnamamide by He(I) and He(II) photoelectron spectroscopy

Abstract He(I) and He(II) excited photoelectron spectra of trans -cinnamic acid and cinnamamide are presented and discussed. The spectra are assigned by comparison with related molecules and by analysis of the relative band intensities in the He(I) and He(II) spectra. The electronic effects of phenyl substitution are described.