The chemistry of binuclear palladium(II) and platinum(II) complexes

The chemistry of binuclear palladium(II) and platinum(II) complexes has been reviewed. This review deals with complexes derived from various classes of ligands and covers various aspects, viz. synthesis, spectroscopic and structural features and chemical reactivity, of these complexes. Applications of these complexes are briefly described in the respected sections.     

Carbon-beryllium binding in CH2Be

Ab initio molecular orbital theory is used to study carbon-beryllium binding in the lowest singlet and triplet states of CH₂Be. When electron correlation is included, both singlet and triplet states are significantly bound relative to the ground states of CH₂ and Be fragments.     

The electronic structure of molecules by a many-body approach

The vertical valence ionization potentials of cyclopropane, ethylene oxide and ethylene imine are calculated by a many-body Green's function method. For C₃H₆ the ordering of the ionization potentials is 2e(), 1e(), 2a₁(), 1a₂(), 1e(). The assignment of the 2a₁ and the 1a₂ ionization potentials which has been controversial is thus clarified. The ordering is in agreement with the result obtained via Koopmans' theorem. For ethylene oxide and ethylene imine Koopmans' theorem fails in predicting the correct order of ionic states. For C₂H₄O the ordering of the ionization potentials is 2b ₁(), 4a ₁, 1a ₂(), 2b ₂,3a ₁, 1b ₁(), 1b ₂, 2a ₁ and for C₂H₅N 6a, 5a, 3a, 2a, 4a, 3a, 1a, 2a. The agreement of the computed ionization potentials with the experimental values is very satisfactory.     

Ab initio Calculations of the potential energy surface of the reaction of singlet methylene with the hydrogen molecule

The potential energy surface for the insertion of singlet methylene into H₂ has been computed on theab initio SCF level as well as with inclusion of electron correlation by means of the CEPA method. The results are compared with those of previous semiempirical,ab initio SCF and CI calculations. The system is a prototype of a reaction where an allowed and a symmetry-forbidden path can compete. The electron correlation energy was found to be very different for different regions of the surface, but did not have much influence on the optimum reaction path. From the computed heat of the reaction, the heat of formation of singlet methylene was estimated to be 101.5 kcal/mol. According to the calculations the reaction does not need any activation energy.     

Temperature deactivation of excited Tb3+ in the presence of 1,2-dioxetane in acetonitrile

Quenching the fluorescence (FL) of terbium perchlorate by 2,2-adamantane-2,2-dioxide (1) was shown to have a chemical character and was caused by the formation of the [1...Tb³⁺] complex. The dependence of the lifetime () of FL of Tb^*3+ in acetonitrile on the temperature and concentration of1 has been studied. The temperature dependence of is caused by a rearrangement of the inner sphere of the aquasolvate complexes of Tb³⁺, which leads to the replacement of H₂O with MeCN and1. The energy of replacing the H₂O molecule in the inner sphere of complexes with a solvent molecule has been calculated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1762–1766, October, 1994.     

Geometrical Changes and Their Energies in the Formation of Donor–Acceptor Complexes

We have mapped the energy demands of the geometrical changes in donor–acceptor complexes BH₃NH₃ and AlCl₃NH₃ and in the course of their formation from their monomers. We have varied the individual geometrical parameters systematically and performed ab initio quantum chemical calculations for these structures. We investigated the energy requirements to change bond lengths and bond angles in both the monomers and complexes and the angles of torsion in the complexes. The changes of bond lengths require more energy in the monomers than in the complexes. The energies to change the acceptor bond angles in the monomers are markedly higher than in the complexes. The changes in the geometrical parameters during the complexation process are more moderate in donors than in acceptors, in agreement with prior experimental observations. The geometry versus energy variations related to the process of complexation are in agreement with the notion of relative rigidity of the donor parts and the more compliant nature of the acceptor parts as well as with the notion of competing effects in the structures of the complexes.     

Intensity distribution in the vibronic side bands of the Γ7(2 T 2g ) → Γ8(4 A 2g ) origin of ReX 6 2- doped K2PtCl6-type crystals

Intensities of vibronic transitions are calculated using an electronic vibrational coupling scheme of symmetrized and localized interactions. The model consists of an active central ion subject to a valence force field originating from nearest-neighbor displacements. The intensities of vibronic fundamentals are obtained from a generalized Lorentzian line shape function which is applied to the ₇(² T _2g ) ₈(⁴ A _2g ) transition of ReCl ₆ ^2- and ReBr ₆ ^2- in various cubic host crystals A₂MX₆ (A = Rb, Cs; M = Te, Sn, Pb; X = Cl, Br). Relative intensities of the odd vibronic side bands are calculated without knowing actual values for ligand field and spin-orbit coupling parameters, and considering only octahedral vibrational frequencies. The sidebands acquire intensity by a coupling which is cubic in the electron coordinates and linear in the nuclear normal coordinates. With some necessary approximations the present model is able to reproduce the experimental intensity distribution satisfactorily.Dedicated to Professor Dr. H. Hartmann on the occasion of his 65th birthday     

Über die Synthese von Dihydro-1,2,3,5-thiatriazol-1,1-dioxiden, 2. Mitt.

By reaction of several N-phenyl-benzamidrazones with SO₂F₂ 2-phenyl-2,5-dihydro-1,2,3,5-thiatriazole-1,1-dioxides2 a–c are formed. By reaction of N,N-diethyl-N-chlorosulfonyl-chloroformamidine8 with hydrazines the corresponding 4-diethylamino-substituted derivatives9 a–d are obtained. Methylation of2 b yields two isomeric products5 and6, whereas by methylation of9 d only one product9 b is obtained.

     

Theoretical studies of atmospheric molecules: SCF and correlated energy levels for the NO2, NO 2 + and NO 2 − systems

SCF and MC-SCF/CI calculations were carried out on the low-lying electronic states of NO₂, NO ₂ ⁺ and NO ₂ ^– , using a double-zeta quality basis set of contracted Gaussian functions. The calculations were performed primarily at the equilibrium geometry (R _NO = 2.25 a_o, _ONO=134 °) of theX ² A ₁ state of NO₂. SCF calculations on NO ₂ ⁺ in a linear conformation were also performed. Results are presented and compared with experiment and other calculations.Research supported in part by Air Force Delivery Orders F33615-72-M-5015 and MIPR889474-00117 and Air Force Office of Scientific Research and in part by the United States Energy Research and Development Administration.     

Non-additivity in water-ion-water interactions

The three-body system Li⁺(H₂O)₂ was analyzed to study that non-additive part of the interaction potential which can be obtained by the Hartree-Fock approximation.For long and intermediate distances the three-body correction was found to be well represented by the induction energy, where bond dipoles are induced on each water molecule by point charges located on the (unpolarizable) lithium ion and on the other molecule respectively: for shorter distances this approximation was corrected by means of an exponential repulsive term. Such a potential model for non-additive interactions was extended to the more general situation Li⁺(H₂O)_n, and Monte-Carlo calculations were carried out on clusters containing up to six water molecules; comparison with other simulation results and with available data showed a significantly improved agreement with experiment. Tentative values for H are presented for n =7, 8,..., 20, where experimental data are not available.