NMR (195Pt and 13C) contribution to the study of some Pt(II), Pt(IV) and mixed-valence thioamido complexes

The ¹⁹⁵Pt and ¹³C chemical shifts (δ_Pt and δ_c) are reported for platinum(II), platinum(IV) and class II mixed-valence complexes, with general formula [PtL₄]X₂, cis- and trans-PtL₂X₂, PtL₂X₄ and Pt₂L₄X₆ (where L may be thiourea, 2-imidazolidine-thione, tetrahydro 2-pyrimidinethione, thiocaprolactam, pyridine-2-thione and tetramethylthiourea, and X may be Cl or Br). The ¹⁹⁵Pt chemical shifts can be understood in view of ¹³C data in terms of variations of electronegativities and σ-donor abilities of ligands attached to platinum.     

Effects of chemical shift anisotropy and 14N coupling on the 1H and 195Pt nuclear magnetic resonance spectra of platinum complexes

Broadening of the ¹⁹⁵Pt satellites in the ¹H NMR spectrum of trans-Pt(ethene)(2-carboxy-pyridine)Cl₂ at high field arises from relaxation of ¹⁹⁵Pt via the chemical shift anisotropy mechanism. We also demonstrate that well-resolved ¹⁴N-¹⁹⁵Pt couplings can be observed in ¹⁹⁵Pt NMR spectra of Pt(II) and Pt(IV) amine complexes, including anti-tumour agents, at elevated temperature where scalar coupling contributions to ¹⁹⁵Pt relaxation are much reduced.     

Some diels—alder reactions of η1-bonded cyclopentadienylmetal compounds

Bis(cyclopentadienyl)mercury readily undergoes Diels—Alder reactions with RCCR (R = CO₂Me or CF₃), CF₃CFCFCF₃, CF₃CFCF₂, (CF₃)₂CC(CN)₂, C₂(CN)₄ and Ph$\text{NCONNC}$O to give stable adducts characterised by¹H, ¹⁹F and ¹³C NMR, spectroscopy. Similar reactions of CF₃CCCF₃ and CF₃CFCFCF₃ with the cyclopentadiene derivatives Me₃MC₅H₅ and (Me₃M)₂C₅H₄ (M = Si, Sn) are also described.     

The 1A1 π→π* state of formaldehyde

The ¹A₁ π→π^* state of formaldehyde is predicted to be 11.2 eV above the ground state and not diffuse.     

31P and 195Pt NMR spectra of [Pt(PPh32(μ-η2-C2H4−nXn)] (n = 0 … 4; X = CN,COOMe)

³¹P and ¹⁹⁵Pt NMR measurements on compounds of the type [Pt(PPh₃)₂ (μ-η²-C₂H_4?nX_n)] (n = 0…4; X = CN, COOMe) are reported and discussed.     

Molecular relaxation processes in very dilute systems: A 13C NMR study of alcohols in alkanes

¹³C T₁ relaxation times have been determined for n-butanol in C₆D₁₂ in the concentration range 0.001 ? _x ? 1 (using ¹³C labelled alcohol) and for t-butanol in the range 0.01 ? _x ? 1. In the former case, this has allowed us to probe molecular mobility down to the region of monomeric alcohols. Comparison with previous results from measurements of ¹H chemical shifts, dielectric relaxation, and the picosecond dynamics of electron solvation allows us to build up a detailed picture of molecular clustering and liquid structure in alkane—alcohol mixtures. For n-butanol, the local liquid structure is established by x = 0.2 while t-butanol does not appear to form aggregates larger than trimers until x = 0.5.     

A preliminary investigation of the thermal and X-ray induced degradation of cellulose nitrates by FAB/SIMS and 13C NMR

Some surface aspects of the thermal and X-ray induced degradation of a cellulose nitrate have been studied by FAB/SIMS.The pristine material gives peaks at 30 and 46 amu, indicative of NO⁺ and NO₂⁺ originating from the nitrate ester groups. The thermally degraded material indicates these peaks at slightly lower intensities, whereas the X-ray degraded material shows little evidence for their appearance. These data complement recent ESCA data on the same systems.¹The conclusion is that electromagnetic degradation is predominantly a surface effect, whereas thermal degradation is a bulk oriented phenomenon. ¹³C nmr has been used to add further evidence for this last point.     

The rα-structure of thieno[2,3-b] thiophene. A 1H-NMR study in a nematic phase including 13C-satellites in natural abundance

The ¹H-NMR spectrum of thieno[2,3-b]thiophene in a nematic phase has been recorded and analysed. The ¹H,¹³C dipole—dipole couplings were obtained from ¹³C satellites in natural abundance. The indirect ¹H,¹H and ¹H,¹³C spin—spin coupling constants were determined from an isotropic sample. The dipole—dipole couplings were corrected for harmonic vibrational contribution. The corrected dipole—dipole couplings were used to evaluate the r_α-structure of the molecule.     

Charge-transfer absorption spectra between tetracyclo[3.2.0.02,7.04,6]heptane and π-type electron acceptors

Charge-transfer transition energies, association constants, and molar extinction coefficients of complexes between tetracyclo[3.2.0.0^2,7.0^4,6]heptane(quadricyclane) and olefine type or quinone type acceptors were measured in methylene chloride at 20°. An excellent linear relationship (r = 0·9938) with a slope of 0·96 was observed in plots of ν_max(CT) for a series of complexes of quadricyclane against ν_max(CT) for the corresponding complexes of N,N-dimethyl-aniline, indicating that quadricyclane forms electron donor-acceptor complexes of weak interactions. The first ionization potential, estimated from the hyperbolic relationship between the charge-transfer transition energy (E_CT) and the ionization potential, was an exceptionally low value (8·28–8·32 eV) for a saturated hydrocarbon and was indeed in the same order of magnitude with that of norbornadiene, which was well reproduced by EHM and MINDO/1 calculations applying Koopmans' theorem to the calculated HOMO energy.     

Assignment of the 13C NMR resonances in trialkylphosphines from spin-lattice relaxation time measurements

Analysis of the ¹³C NMR chemical shift and coupling constant data for a number of straight-chain aliphatic trialkylphosphines and their transition metal carbonyl complexes suggests that complexation leads to: (1) a deshielding of C(1) and an increase in ¹J(¹³C³¹P), (2) a slight shielding of C(2) and a decrease in ²J(¹³C³¹P), and (3) little or no change in the chemical shift for C(3) and a slight increase in ³J(¹³C³¹P). Application of these rules to the assignment of the ¹³C NMR spectrum of P(butyl)₃ led to conflict with prior work. A study of segmental motion in these derivatives via spin-lattine (T₁) relaxation time measurements was therefore performed, and these data are in complete agreement with the proposed assignments. These generalizations must be applied with care, however, since the presence of either unsaturation or branching near the phosphorus can interfere with this pattern.     

A non-empirical LCAO-SCF-MO investigation of cross sections through the potential energy surface for the [C2H2Cl]+ systems; comparison with the [C2H5+] and [C2H4F]+ systems

Non-empirical LCAO MO SCF calculations are reported on cross sections through the C₂H₄Cl⁺ system and comparisons are drawn with the C₂H₅⁺ and C₂H₄F⁺ systems. Barriers to rotation in the classical 1- and 2-substituted ethyl cations have been computed and an investigation made of the bridged chloronium and fluoronium ions. The results suggest that the relative stabilities of bridged ions with respect to the corresponding classical 2-substituted ethyl cations increase in the order H < F < Cl. The results are discussed in terms of available experimental data and consideration given to correlation and solvation energy effects.     

A sensitivity analysis of a diatomics-in-molecules model of the 1A′ states of H2O

A method for computing the sensitivity of diatomics-in-molecules (DIM) potential energy surfaces (PES) to variations in the parameters characterizing the diatomic fragment matrices is applied to the ¹A′ states of H₂O. The analysis, presented explicitly for 2 × 2 and 3 × 3 fragment matrices, identifies those parameters having the largest influence on local features of the PES. Estimates of the parameter alterations necessary to effect specific changes in the PES are easily provided, allowing manipulation of the DIM model so as to obtain a good overall representation of the PES. Local regions of the PES turn out to be sensitive to only a few parameters and are largely unaffected by the rest. This supports the notion, customary in reaction dynamics, that processes may be discussed qualitatively in terms of the local properties of a PES such as the position of a barrier or the type of energy release.     

Studies on the compounds in the BaFeS system. I. Linear chain antiferromagnetism of Ba2FeS3 and related compounds Ba2CoS3 and Ba2MnS3

Magnetic susceptibilities of Ba₂FeS₃, Ba₂CoS₃, and Ba₂MnS₃ show rounded maxima at 130, 125, and 100 K, respectively, which are due to quasi-one-dimensional antiferromagnetic short-range ordering. Intrachain interactions, $\text{J}\text{k}$, are estimated to be ?20, ?15, and ?12 K, respectively. ⁵⁷Fe Mössbauer spectra of Ba₂FeS₃ and ⁵⁷Fe-doped Ba₂CoS₃ and Ba₂MnS₃ at 4.2 K show long-range antiferromagnetic ordering, due to the interchain interaction. The profile of Mössbauer spectra at 4.2 K is analyzed based on the coexistence of magnetic hyperfine and quadrupole interactions, and magnetic hyperfine fields at 4.2 K are estimated to be 36, 29, and 59 kOe, respectively.     

2P12 excited iodine formation in the F + HI reaction

Fluorine atoms produced in a microwave discharge of SF₆ were mixed with HI molecules in a flow system. Groundstate and excited iodine atoms were monitored by measuring the absorption of atomic emission lines from an iodine resonance lamp. A model taking into account the formation of excited iodine atoms through the reactive channel as well as the VE energy transfer process from vibrationally excited HF molecules is discussed. The fraction of excited iodine atoms formed in the reaction is shown to be 0.5.     

17O and 183W NMR studies of the paratungstate anions in aqueous solutions

¹⁷O (40.7 MHz) and ¹⁸³W (12.5 MHz) NMR spectra of aqueous Na₁₀[H₂W₁₂O₄₂]·27H₂O (1), Na₆[W₇O₂₄]·14H₂O (2) and (NH₄)₆[Mo₇O₂₄]·nH₂O solutions, as well as of 2, 1 and 0.1 M Na₂WO₄ and 2 M Li₂WO₄ solutions acidified up to P = 0.5, 1 and 1.14 have been measured. The composition of the W₇O₂₄^6? anion remains unchanged (2), its structure being similar to that of Mo₇O₂₄^6?183W NMR spectrum shows three resonances with the chemical shifts + 269.2, ?98.8 and ?178.9 ppm relative to WO₄^2? and intensity ratio 1:4:2. “Paratungstate A” produced during polycondensation of WO₄^2? at P ? 1.17 is identical with heptatungstate W₇O₂₄^6?. The [H₂W₁₂O₄₂]^10?183W NMR spectrum in the acidified 2 M Li₂WO₄ solution has four resonances with the chemical shifts in the range - 105–145 ppm and intensity ratio 1:2:1:2. As suggested by NMR data, the H₂W₁₂O₄₂^10? ? W₇O₂₄^6? transformations occur, which depend upon concentration and temperature.     

Actinide-centered cyclometalation chemistry. An unusually distorted thorium bishydrocarbyl: Thp[η5-(CH3)5C5]2CH2Si(CH3)3]2

The crystal and molecular structure of the complex Th[η⁵-(CH₃)₅C₅]₂[CH₂-Si(CH₃)₃]₂, which undergoes facile intramolecular cyclometalation to the thoracyclobutane Th[η⁵-(CH₃)₅C₅]₂(CH₂)₂Si(CH₃)₂, is reported. While the Th[η⁵-(CH₃)₅C₅]₂ ligation is unexceptional, the Th[CH₂Si(CH₃)₃]₂ fragment is highly unsymmetrical having Th-C (corresponding angle Th-C-Si) 2.51(1) Å (132.0(6)°) and 2.46(1) Å (148.0(7)°). This conformation, which appears to result from severe intramolecular non-bonded contacts, allows a methyl hydrogen atom of one CH₂Si(CH₃)₃ ligand to approach within ca. 2.3 Å of the α-carbon atom of the other CH₂Si(CH₃)₃ ligand.     

A relation between 73Ge chemical shifts and CNDO/2 charges in tetrahalogenogermanes

Using Hojer and Meza's extension of the CNDO/2 method to third row elements, a linear relationship is established between the calculated atomic charges on the Ge atom in germanium tetrahalides GeCl_nBr_4-n (n = 0, 1, 2, 3, 4) and their recently measured ⁷³Ge chemical shifts.     

13C-NMR study of the role of tunnelling in the tautomerism of pyrazole

¹³C-NMR is used to study the mechanism of proton transfer in tautomeric rearrangements of pyrazole and its d_t-derivative.