Charge transfer spectra of organometallic complexes—IX. Evaluation of solvent effects on the electron donor—acceptor interactions between trimethyltinisothiocyanate and iodine

Charge transfer energies of trimethyltinisothiocyanate—iodine complexes in solution are found to depend on the nature of the solvent. The relationship of these solvent shifts with various solvent properties, and is discussed. Stabilization energies of the excited states in the different solvents are determined using the Onsager theory of dielectrics.     

Charge transfer spectra of organometallic complexes—II. Determination of the donor site in trialkyltinhalides

The charge transfer spectra of several trialkyltiniodide- and bromide-iodine systems are presented. Interpretation of the blue shift, the charge transfer band maximum and the formation constant data leads to the conclusion that, on complexation with iodine, the halide atom is the preferred donor site in the trialkyltinhalide molecule.     

Molecular complexes of cyclophanes—XIII. Charge-transfer complexes of cyclophanes with fluoranil

The charge-transfer (CT) complexes of some methylated [2.2]para-, multibridged cyclo- and [2.2]indenophanes as π-donors with fluoranil (TFQ) as π-acceptor have been studied spectrophotometrically. The role of the molecular structure of the donors on their Lewis basicities and stability of their CT complexes with TFQ are discussed. Eight pure crystalline complexes were prepared. Their i.r. spectra indicate an increase of the electron density in the TFQ part of the CT complex.     

Infrared spectra of hexamethylbenzene—tetracyanoethylene complexes at high pressures

Infrared spectra of hexamethylbenzene(HMB)—tetracyanoethylene(TCNE), 1:1 and 2:1, complexes were measured under high pressures, 11̃4,000 bar. It was found that the CC stretching (A_g) band of TCNE became much stronger at high pressures than at 1 bar and that the intensity increase of this band was especially large for both of the complexes. Based on these facts the strong appearance of the CC band at 1 bar, which is inconsistent with the symmetry consideration derived from X-ray analysis, can be discussed.     

NMR study of donor—acceptor complexes—III. 31P resonance of arylphosphines and arylphosphine chlorides and their complexes with BBr3, and BCl3.

The ³¹P NMR spectra of (4X—C₆H₄)_nPCl_3—n, (3X—C₆H₄)_nPCl_3—n (X = F, Cl, H; n = 1, 2, 3) molecules and of their donor—acceptor complexes with BBr₃ and BCl₃ are reported. The chemical shift increments on complexation δ^P—B are interpreted in terms of increased charge on the P-atom and of concomitant charge delocalisations: π(p—p)A$\text{←}\text{r}$—P and P$\text{→}\text{—}$Cl and π(p—d)A$\text{→}\text{r}$—P and P$\text{←}\text{—}$Cl in general and of mesomeric contributions in the case of the (4FC₆H₄)_nPCl_3—n compounds and their complexes.     

Molecular complexes with aromatic cations as electron-acceptors—III. Charge-transfer spectra of substituted pyrylium thiocyanates,selenocyanates and iodides

Alkyl- and/or aryl-substituted pyrylium salts were converted, on grinding with the corresponding alkali salts, into thiocyanates, selenocyanates and iodides, whose electronic and vibrational absorption spectra were recorded. Charge-transfer bands were evidenced, even when they overlapped with absorption bands, by a compensation technique. A comparative discussion of charge-transfer spectra for pyrylium thiocyanates, selenocyanates and iodides is presented, accounting for the effect of one α- or γ-phenyl-substituent in thio- and selenocyanates which is opposite to that in the iodides. A pronounced negative solvatochromy of the CT band is observed. The donor ability of anions for the CT band of pyrylium salts increases in the order Br⁻<SCN⁻<SeCN⁻<I⁻. Correlations with ionization potentials I_D of these anions are presented, allowing an estimation of I_D's for SCN⁻ and SeCN⁻.     

Charge-transfer complexes of benzanilides with π-acceptors

Spectrophotometric studies of several substituted benzanilides as electron donors with tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) as electron acceptors have given results that are consistent with an interpretation of 1:1 charge-transfer (CT) complexes. The nature of interaction as well as the substituent effects on the CT complexation are discussed.     

New description of the substituent effect on electronic spectra by means of substituent constants—IV. Charge transfer spectra of EDA complexes of tetracyanoethylene with meta-disubstituted benzenes

Charge transfer spectra of EDA complexes composed of TCNE and various kinds of m-disubstituted benzenes are discussed on the basis of a general equation, theoretically derived to express the substituent effect on electronic spectra. Molecular orbital calculation shows that the HOMO of the substituted benzenes is divided into two groups. One has a₂-like character and the other b₂-like, so that the substituent effect on the CT spectra has been also classified into two groups, since the CT spectral character is different in the two. This viewpoint is supported by the application of the general equation to the CT spectra. Also, we have applied the equation successfully to the other typical π-π or n-σ type EDA complexes.     

Vibrational spectra of carboxylato complexes—IV. Mixed-metal and mixed-valence oxo-trinuclear complexes

Infrared spectra of mixed-metal complexes [Cr_3-nFe_nO(OOCR)₆L]⁺ (n = 1,2; R = H, CH₃; L = H₂O, γ-picoline, pyridine), and of mixed-valence complexes [Fe^III₂Fe^IIO(OOCCH₃)₆py₃], [Ru^III₂Ru^IIO(OOCCH₃)₆L₃] (L = H₂O, P(C₆H₅)₃) are reported and compared with analogous symmetrical (Cr^III)₃, (Fe^III)₃ and (Ru^III)₃ species. The effects of lowered symmetry are seen in the mixed-metal but not in the mixed-valence complexes.     

New description of the substituent effect on electronic spectra by means of substituent constants—VI. Utraviolet spectra of 4-substituted pyridine N-oxides and blue shifted iodine bands of their EDA complexes with iodine

Electronic spectra of 4-substituted pyridine N-oxides and their EDA complexes with iodine were studied. The substituent effect on the near u.v.¹A₁ intramolecular CT bands of the N-oxides and on the blue shifted iodine bands caused by CT complex formation are discussed in terms of a general equation, theoretically derived in order to describe the substituent effect on electronic spectra by means of substituent constants. The results are quite successful and supported by semi-empirical SCFMO-CI calculations. Based on the results mentioned above, the character of n-σ type N-oxide—iodine CT complexes is also examined. The complex formation constants (log K) and pK_a values of the N-oxides correlate especially well, indicating that the CT interaction mechanism cannot be neglected in proton addition reactions such as hydrogen bonding and pK_a values.     

Vibrational spectra of carboxylato complexes—II. Some oxo-tetranuclear complexes

The i.r. and Raman spectra of the compounds Be₄O(OOCCH₃)₆, Be₄O(OOCCD₃)₆, Be₄O(OOCH)₆ and Zn₄O(OOCCH₃)₆ have been analysed and assigned in detail. In particular, the vibrational modes of the O(MO₃)₄ subunits, and their interactions with the carboxylate ligand vibrations, have been identified. The compound Zn₄O(OOCC₂H₅)₆ has the same oxo-centred structure as the others.     

Unusual supramolecular donor—acceptor complexes of bis(crown)stilbenes and bis(crown)azobenzene with viologen analogs

The results of the comprehensive study of novel supramolecular donor-acceptor complexes of bis(crown)stilbenes and bis(crown)azobenzene with viologen analogs are generalized. The original methodology for self-assembling of the organic donor-acceptor complexes possessing a very high thermodynamic stability is described. The hydrogen bonds between the peripheral fragments of the donor and acceptor play the key role in the self-assembling. The influence of different structural factors on the thermodynamic stability of the supramolecular donor-acceptor complexes and the efficiency of charge-transfer interactions between the donor and acceptor are discussed. The driving forces of the reaction leading to exotic trimolecular charge-transfer complexes are considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 779–787, April, 2008.     

Modelling the molecular weight distribution in terpolymerization systems with donor–acceptor complexes

In this work we present, for the first time, a mathematical development of the moments of the molecular weight distribution in terpolymerization systems where donor–acceptor complexes are formed and the propagating reactions are carried out according to the complex participation model. The resulting set of equations is applied to the system formed by vinyl chloride (VC), vinyl acetate (VAc) and maleic anhydride (MA), in order to show the use of the equations and the type of information that might be obtained from them.     

The infrared spectra of complexes with planar dithiooxamides—III. The Ni(II) polymeric complexes

Thermal analysis, u.v. spectra and i.r. spectra are given for some nickel complexes and their isotopes of planar dithiooxamides, the results are explained by assuming planar and octahedral S,N conformations about the nickel atoms in a polymeric structure.     

Charge transfer spectra of organometallic complexes—VIII. Energy contributions to the formation of a donor—acceptor complex and to the electron transfer in the interaction between trialkyltindonors R3SnX and (X = NCS,Br) the acceptors,I2 and TCNE

The enthalpies of formation for charge transfer complexes of the type [R₃SnNCS-I₂] (R = Et, iPr), [Et₃SnNCSTCNE] and [R₃SnBrI₂] (R = Me, Et) have been determined by calorimetric measurements. The data are analyzed using Mulliken's resonance structure theory, to produce the different energy contributions to the charge transfer interaction in these complexes.     

Photoelectron spectroscopy of ƒ-element organometallic complexes: VII. Studies of di-cyclopentadienyluranium(IV) complexes containing tetrahydroborate,amido, pivalate and dithiocarbamate ligands

A study of gas phase photoelectron spectra of a series of U(η⁵-C₅H₅)₂X₂ (X = BH₄, NEt₂ O₂CC(CH₃)₃, S₂CNEt₂) complexes has revealed changes in the sequence of upper filled molecular orbitals along the series. In all cases the first ionization event corresponds to removal of uranium 5ƒ electrons. In the case of X = NEt₂, the next highest occupied ligand-based MO is an almost pure N2p lone pair, but in the other complexes this MO is π-ring in nature. The observations are consistent with the higher reactivity of the amido complexes toward molecules containing polar double bonds or acidic hydrogens and with the greater labilities of the UCp bonds in the other complexes.     

Complexation of hypocrellins and bivalent metals and one-electron reduction of the complexes with electron donor

The complexation of HA (or HB) with bivalent metals was examined by UV-Vis andNMR spectroscopy, and all of the complexes obtained have a metal-ligand ratio of 1:1.Thephotoinduced reduction of the complexes of HA-Zn~(2+) and HA Mg2+ (or HB-Zn~(2+), HB-Mg2+)in the presence of 1-benzyl-1,4-dihydro-nicotinamide as the electron donor was investigated byUV-Vis and ESR spectroscopy. The studies demonstrated that illumination of the complexes ofHA(HB)-Zn~(2+) and HA(HB)-Mg~(2+) led to the accumulation of the chelated semiquinone radicalanions.     

Unsymmetrical donor–acceptor oligothiophenes end-capped with triphenylamine and phenyldicyanovinyl units

Highly stable unsymmetrical donor–acceptor oligothiophenes equipped with terminal electron-donating triphenylamine and an electron-withdrawing phenyldicyanovinyl groups have been synthesized. An influence of the length of conjugated oligothiophene π-spacer between the donor and acceptor blocks on solubility, thermal, optical and electrochemical properties of such compounds has been revealed.