Claudio Furlani

On the problem of the vibrational frequencies of water in complexes

Abstract An attempt has been made to calculate the vibrational frequencies of water in aquocomplexes, with particular regard to the shifts of the frequencies of the fundamental vibrations of the free water molecule. On the basis of the electrostatic model of a coordination molecule of the type MeH 2 O , two different types of calculations has been carried out: 1) A potential function of the Van Vleck-Cross type (J. Chem. Phys., 1 , 1933, 357) with additional terms corresponding to the electrostatic interactions between the metal ion and the coordinated water molecule has been developed in series of powers of the internal coordinates in order to obtaine equilibrium positions and values of the force constants; these numerical values have been used to solve the vibrational problem by the usual method of the F , G matrices. 2) A perturbation method with the eigenfunctions of the normal vibrations of the free water molecule as unperturbed wave functions and the operator of the electrostatic interaction metal-water as the perturbation operator has been also used. Both types of calculations have led to the prevision that the two stretching frequencies of water are lowered in the aquocomplexes by an amount of the order of 3–400 cm −3 , while the bending frequency is raised by few tens of cm −1 . Both expectations agree very well with the experimental data.

Electrolytic reoxidation after current reversal in chronopotentiometry

The authors present a theoretical treatment of the problem of determining the transition time of the reoxidation processes which occur after current reversal at the end of an electrolytic reduction in chronopotentiometry, when the reduced form is unstable and is being decomposed according to a first-order reaction. Assuming semi-infinite linear diffusion and equal diffusion coefficients for the reduced and the oxidized form a very simple relation is obtained, connecting the transition times of reduction and of reoxidation with the rate constant of the reaction, independently of all other experimental conditions. The validity of this relation has been tested in the case of the reduction and subsequent reoxidation of Fe3+ in alkaline triethanolamine solution, in the presence of hydroxylamine which acts as a regenerating agent for the oxidized form.

Absorption spectra of some tetrahalogenomanganates (II)

Abstract Tetrahalogenomanganate(II) salts of onium cations exhibit in nonaqueous polar solvents a spectrum which is characteristic of tetrahedral [MnHal 4 ] 2− anions, and consists of several bands grouped in three distinct absorption regions; experimental details on the measured spectra are reported. The observed form of the spectrum can be satisfactorily accounted for on the basis of ligand-field theory predictions for spin-forbidden transitions from the groundstate 6 S of Mn 2+ to excited quartet states of d 5 arising under a field of symmetry T d , assuming Δ∼ 3300 cm −1 . Absorption intensities are higher by a factor 10–100 than the intensities of octahedral Mn 2+ complexes.

Some new complexes of nickel(II) halides with N,N′-disubstituted thioureas

Abstract Some new complexes of nickel(II) halides with sym-diphenyl-, sym-di-n-butyl, symdiallyl-, sym-allylethyl-thioureas have been prepared having general formulas NiL2X2, NiL4X2 and NiL6J2. The compounds of 1:6 type is the first hitherto prepared with substituted thioureas and magnetic studies show that solid compound NiL2X2 have tetrahedral, NiL4X2 tetragonal and NiL6J2 octahedral structures. In all case the thioureas are probably bonded to nickel through their sulfur atom. Magnetic moments of solid 1:4 compound vary with temperature according to a tetragonal structure with a singlet ground state and a thermally populated triplet excited state. In acetone solution all these compounds lose ligands to give tetrahedral species NiL2X2 according to NiLnX2 → NiL2X2 + (n−2) L.

Absorption spectra of the nickel-stilbenediamine complexes

Abstract Absorption spectra of the blue paramagnetic of the yellow diamagnetic isomers of the nickel-stilbenediamine (1 : 2) complexes have been measured and compared with term systems, that have been calculated with the aid of Hartmanns theory of the electrostatic complexes (strong-field and weak-field case) for various possible structures (symmetries O h , T d , D 4 h , D 2 d and C 2 v ). Satisfactory agreement between calculated and observed form of the spectrum of the magnetically normal isomers is obtained if a distorted octahedral structure is supposed for the latters, i.e. a structure with two further ligand groups (probably two anions of the complex salts) in cis- or trans position; but also a distorted tetrahedral structure of symmetry D 2 d cannot be excluded a priori. Removal of the two weaker ligands (whereby the two stilbenediamine molecules are left in a planar tetragonal disposition) turns the complex into a diamagnetic one (yellow form) without any other modification of the geometry of the complex or of the distance central ion-ligand. In the spectrum of the yellow form three very near bands are expected, in substantial agreement with one large band observed. The quantitative agreement between calculated and observed frequency values is less satisfactory; it can be improved if a slight percent of covalent bonding between central ion and ligand groups is assumed.

Oxygenation and oxidation of CoII-chelates☆

Abstract Co II dihistidine and Co II diglycylglycine are known to bind oxygen reversibly (oxygen carriers) and to yield compounds containing the grouping X 2 CoO 2 CoX 2 . It is now shown that the product of the irreversible oxidation does not contain peroxo groups, but corresponds to the general formulae [Co III X 2 (OH) 2 ] − ,[Co III X 2 (OH)].

Crystal polarised spectra, and electronic structures, of some pseudotetrahedral cobalt(II) complexes with ‘soft’ bonding ligands

The crystal polarised spectra of some pseudotetrahedral CoII complexes having chromophores [CoS2Cl2] and [CoP2X2](X = Br–, I–), have been recorded. The spectra may be assigned assuming an effective C2ν symmetry and spin–orbit coupling is found to be less important than the low-symmetry ligand field in modifying the electronic structure derived from Td symmetry. The sequence of components derived from Td symmetry is found to be: 4T1(F) : B1 < A2 < B2; 4T1(P) : B2 < A2 < B1. Crystal-field calculations fit the observed spectra only if parameters of the low symmetry components are treated as merely empirical parameters. Qualitative σ- and π-bonding parameters for the different donor ligands are derived and compared.

Study of the electronic structure of some alkyltin derivatives by means of uv photoelectron spectroscopy

Abstract He(I) photoelectron spectra (UPS) provide data on the orbital energy levels in the valence shells of the following compounds: R 3 SnOR (R = methyl), R 3 Sn(acac) (R = methyl, ethyl, acac = acetylacetonate), R 2 SnCl 2 (R = methyl, n-butyl), R 2 Sn(acac) 2 (R = methyl, n-butyl, acac = acetylacetonate), R 2 Sn(Tacac) 2 (R = methyl, Tacac = trifluoroacetylacetonate). The results are discussed in the light of comparisons with the UPS spectra of simple tin compounds and of the β-diketonates of other metals.

Ultraviolet photoelectron spectroscopic investigation of electronic structure of some organic thio- and isothio-cyanates and their selenium analogues

He(I) photoelectron spectra of CH3SCN and CH3SeCN exhibit a series of five ionization bands < 15 eV, the first four being assigned to a sequence of n, π and σ orbitals of the S(Se)CN group on the grounds both of empirical correlations with simpler molecules, and of semi-empirical and ab initio quantum mechanical calculations. Theoretical calculations are reported and discussed also for the isomeric CH3NCS molecule, already reported in the literature, but re-examined here for comparison. In phenyl-substituted thio- and isothio-cyanates and their selenium analogues, photoelectron spectra are dominated by the presence of strong benzenoid bands, yet some general trends related to structural effects can be recognized.

Spectroscopic evidence of metal–metal interaction in tetrakis(dithiophenylacetato)dinickel(II)

The crystal polarised spectrum of the title compound has been recorded. The spectrum contains more bands than those predicted for a mononuclear diamagnetic square planar NiII complex, a series of five bands with different polarisation characteristics being observed between 13 and 18 kK(1 kK= 1000 cm–1). It is suggested that the spectra are indicative of substantial overlap of the d orbitals between the two nickel(II) atoms in the molecule, and an assignment of the spectrum in D4 symmetry (for the dimeric [Ni2S8] chromophore) put forward.