The effect of selfassociation of mercurated carbonyl compounds of mercury-199 chemical shifts

Temperature and concentration dependences of mercury-199 chemical shifts in benzene solutions of bis(methylethylketone)mercury Hg(CH₂COC₂H₅) (I) and α-bis(methylacetoacetone)mercury Hg(CH₂COCH₂COOCH₃)₂ (II) are determined by the ¹H-{¹⁹⁹Hg}method. The NMR data obtained and the IR spectra are indicative of selfassociation of I and II in solution with the formation of weak intermolecular coordination bonds Hg ← :OC. The enthalpies of complex formation calculated on the assumption of one mercury atom bonding with only one carbonyl function are equal to ?3.2 ± 0.1 kcal/mol and ?2.2 ± 0.1 kcal/mol for I and II, respectively.     

Heteropoly compounds as octahedral high valence complex. Spectrochemical properties of Waugh-structure enneamolybdonickelate(IV) and enneamolybdomanganate(IV) ions

Electronic absorption and magnetic circular dichroism (MCD) spectra in UV-vis region of Waugh-structure [XMo₉O₃₂]^6?(X = Ni(IV), Mn(IV)) ion in aqueous solution and solid IR spectra have been measured. The Ni(IV) ion in the polyanion has a low-spin d⁶ electronic configuration and the Mn(IV) ion has a d³ configuration. Visible absorption spectrum of the nickelate(IV) polyanion is interpreted to be mainly governed by charge-transfer transitions of the “ligand”, Mo₉O₃₂, to Ni(IV) ion, rather than d-d transitions, while visible absorption of the manganate(IV) polyanion is governed, to a great extent, by d-d transitions. It is indicated by the MCD spectrum that the splitting of the first d-d absorption in the manganate(IV) polyanion is due to a contribution of the spin-forbiden transition, rather than from a trigonal splitting of the spin-allowed transition. Absorption and MCD spectra in UV region are due to charge-transfer transition within a common “ligand”, which are less influenced by the kind of heteroatom, Ni(IV) or Mn(IV). The MCD pattern by the intra-ligand charge-transfer is especially characteristic of the Waugh-structure polyanions.     

The crystal and molecular structure of hexadecaphenyloctasiloxyspiro(9,9)titanate(IV)

The crystal and molecular structures of the title compound have been determined by single crystal X-ray diffraction methods. In the spiro molecule, the metal atom has a geometry very close to tetrahedral, with OTiO angles of 107.9–111.0(2)° and very short TiO bonds of length 1.777–1.791(5)Å. The two TiO₅Si₄ rings have different, ill-defined conformations; the SiO bond lengths and SiOSi angles are similar to those in (SiO)_n rings.     

A 19F NMR study of the transmission of electronic effects in triarylantimony and triarylbismuth compounds. A comparison with the nitrogen- and carbon-containing analogues

A ¹⁹F NMR study of the transmission of electronic effects has been made for the systems Ar₂EC₆H₄F-4 (E = Sb, Bi, CH, N). The fluorine chemical shifts obtained are correlated with the polar constants (Σσ^o and Σσ) of the substituents, suggesting that electronic effects are transmitted through the SbC_ar, BiC_ar and CC_ar bonds predominantly by an inductive mechanism, whereas the transmission through the NC_ar bonds is contributed to significantly by classical resonance effects due to competitive conjugation of the lone pair with the aromatic rings, and the substituents therein. A dual parameter correlation of the fluorine chemical shifts with the inductive (σ_I) and resonance (σ^o_R and σ_R) parameters of the substituents in the aromatic rings has led to similar conclusions. The inductive transmission through the bridging Sb and Bi atoms has been assigned to the absence of conjugation of lone pair and vacant d-orbitals of the metals with π-electron systems of the aromatic rings. On the basis of the values of the ? coefficients for the correlation equations obtained it has been established that the transmitting ability of the BiC_ar bonds is close to that of the C_alC_ar bonds and considerably lower than the transmitting ability of the NC_ar bonds.     

Thermal decomposition of anionic organoaluminum compounds : V. The preparation and crystal structure of the (isopropylideneamino)dimethylaluminum dimer

The thermolysis of K[Al₂(CH₃)₆SCN] at 120° leads to the formation of [(CH₃)₂AlNC(CH₃)₂]₂. Verification of the dimeric configuration of (isopropylidenamino)dimethylaluminum has been obtained from three-dimensional X-ray data measured by counter methods. [(CH₃)₂AlNC(CH₃)₂]₂ crystallizes in the triclinic space group P$\text{1}$ with cell dimensions a 7.027(4), b 7.760(4), c 8.583(4) Å, α 115.70(5)°, β 105.72(5)°, γ 92.38(5)°, and ?_calc 0.94 g/cm³ for Z = 1. Leastsquares refinement gave a final conventional R value of 0.058 for 1230 independent reflections. Proposed structures of the parent 2/1 complex, as well as mechanisms for the formation of (isopropylidenamino)dimethylaluminum are discussed.     

The crystal structure of dichlorodimethyltin(IV) 1/1 tetramethylurea adduct

The results of a single crystal X-ray diffraction study of dichlorodimethyltin(IV) 1/1 tetramethylurea adduct are reported. The compound is five-coordinated with a distorted trigonal bipyramidal geometry.     

The 31P NMR spectra and structure of some compounds containing phosphonium ions in 25-oleum solution

25-oleum has proved to be an extremely useful solvent for recording the ³¹P NMR spectra of a variety of compounds containing phosphonium ions. Not only have data in very good agreement with previous solid state and solution results been obtained, but the structures of some solids containing mixtures of phosphorus (V) species have been ascertained for the first time.     

NMR study of extracted compounds of trioctylalkylammonium with rare earth nitrates

¹H and ¹³C NMR was used to investigate the structure of ion pairs formed by trioctylalkylammonium (alkyl = CH₃-C₈H₁₇) cation and rare earth-containing anions in nitrobenzene. The cation-anion distance in the investigated compounds increases from trioctylmethyl to trioctylbutylammonium salt, remaining constant with further growth of the n-alkyl chain. The ion pair formation changes the conformation equilibrium of the cation alkyl radicals to make easier the cation-counter-ion contact.     

Polarographic study of Sn(IV) chloride-pyridine N-oxide complexes in acetonitrile

Polarograms recorded of Sn(IV) chloride in acetonitrile in the presence of controlled quantities of each of nine substituted pyridine N-oxide ligands demonstrated the formation of stable and soluble complexes with a stoichiometry dependent upon the nature and position of the ring substituent. The polarographic data associated with each complex and the free ligands are used to substantiate a proposed bonding model which explains the dependency of the complex formula on the ligand structure. The salt SnCl₄·5H₂O was employed as a source of Sn(IV) and the complete polarographic behaviour of this salt in acetonitrile is described as a basis for the interpretation of complex reduction behaviour.     

The formation of flouride complexes of titanium(IV)

The complex formation equilibria between titanium(IV) and fluoride ions have been studied at 25°C in 3 M(Na)Cl ionic medium by measuring, with an ion selective electrode for F^?, the free HF concentration in acid Ti(IV) solutions. The [H⁺] was kept within 0.25 and I M where the predominant form of uncomplexed metal is the dihydroxotitanium(IV) ion, Ti(OH)²⁺₂. The potentiometric data have been explained by assuming Ti(OH)₂F⁺, TiF₄ and HTiF^?₆, with equilibrium constants given in Table 3. Within the accuracy of the present e.m.f. study, ±0.2 mV, no evidence for intermediate complexes bearing 2, 3 and 5 F^? was found.From a special series of measurements, carried out by replacing a large part of the Cl^? with ClO^?₄, it is concluded that no appreciable amount of Ti(IV)Cl complexes is formed at the 3 M level employed as ionic medium.     

Theoretical study of the static Jahn-Teller effect—I. Two-mode vibronic coupling in octahedral halocomplexes with doubly degenerate electronic states

A two-mode E_g-(a_1g+e_g) vibronic coupling is analyzed for octahedral systems. Analytic formula for the adiabatic potential surface (APS) is obtained considering quadratic vibronic terms and anharmonicities of normal vibrations as well. Potential constants, viz. five elastic force constants and three vibronic constants, are evaluated from the numerical map of the APS applying the non-linear regression analysis. Numerical values are obtained for hexahalocomplexes on the CNDO/INDO level of total energy calculations.     

Preparation,molecular structure and electronic structure of the rhombic,six-coordinate niobium(IV) complex NbCl2(ButC(O)CHC(O)But)2

The compound trans-NbCl₂(dpm)₂, Hdpm = 2,2,6,6-tetramethylheptane-3,5-dione, has been prepared and the molecular structure determined in each of two crystalline polymorphs by X-ray diffraction. The visible spectrum and the EPR spectrum have been measured and a Fenske—Hall calculation performed. The combined results give a reasonable and internally consistent picture of the electronic structure of the molecule. The HOMO is a b_3g-orbital (predominantly d_yz), while the two lowest-lying unoccupied orbitals (ca 16,000 cm^?1 higher) are b_2g(sim; d_xz) and a_g(sim; d_x²_?y²) orbitals, all in the D_2h-symmetry. The b_3g → b_2g and b_3g → a_g transitions are observed at 588.4 and 626.7 nm. The EPR spectrum in solution is a decet; the measured value of <g > is 1.930 and <A_iso > is 149 G. For the crystalline polymorph 1 the crystal data are: orthorhombic (P2₁2₁2₁), a = 13.649(3) Å, b = 18.166(4) Å, c = 11.425(4) Å, V = 2833(2) ų and Z = 4. Polymorph 2 is monoclinic (P2₁/n) with a = 12.288(5) Å, b = 9.226(4) Å, c = 12.545(4) Å, β = 94.24(3)°, V = 1418(2) ų and Z = 2. The molecule in 2 is centrosymmetric with virtual D_2h-symmetry. In 1 there are distortions in the chelate plane postulated to be due to packing forces. The two forms have comparable averaged values of interatomic dimensions.     

the 31P NMR chemical shifts of four-, five- and six-coordinate phosphorus(V) compounds

There appears to be a correlation between the ³¹P chemical shift differences between A⁺ and AX (Δ₁), and between A⁺ and AX₂^? (Δ₂), where A⁺ is a phosphonium ion and X is an anionic ligand. This relationship holds for a wide range of substituents on phosphorus, despite the expected changes in hybridisation along the series, and is very useful for predicting the shifts of new or unknown species.     

Ligand promoted reductive elimination from Zr(IV). The preparation of zirconacycles from alkylzirconium(IV) hydrides and alkynes

Alkynes induce reductive elimination of alkane from Cp₂Zr(H)(R); zirconacyclopentadienes are formed as well.