Change In Coordination Number Research Articles

Auto-association in organotin compounds: butyltin trialkoxides

The hitherto unreported series of n-butyltin trialkoxides, BunSn(OR)3, where R = Prn, Pri, Bun, Bui, Bus, But, and neopentyl, has been prepared. 119Sn Chemical shifts at several dilutions and temperatures have been measured by heteronuclear magnetic double resonance, and are discussed in terms of changes in co-ordination number of the tin. These depend upon the steric effect of the alkoxy-groups.

Determination of co-ordination number in some compounds of magnesium and aluminium: a comparison of X-ray photoelectron (ESCA) and X-ray emission spectroscopies

The effect of changes in co-ordination number (four to six, oxygen ligands) upon 2p and 2s ionisation energies of magnesium and aluminium is shown to be about ten times greater (i.e. ca. 2 eV) than the effect upon the Kα emission energy, X-ray photoelectron spectroscopy (ESCA) is therefore to be preferred to X-ray emission spectroscopy for the determination of co-ordination number; at constant co-ordination number orbital energies are also affected by the nature of the ligands.

Die Koordinationszahl von Lanthaniden: Thermodynamik der LnIIIEDTA‐Mischkomplexe mit den Anionen der 8‐Hydroxychinolin‐5‐sulfonsäure, Iminodiessigsäure und Nitrilotriessigsäure

AbstractThe values of ΔG, ΔH and ΔS for the formation of the mixed 1:1:1 lanthanide EDTA complexes with the anions of 8‐hydroxyquinoline‐5‐sulfonic acid, iminodiacetic acid and nitrilotriacetic acid were determined by pH‐titrations and a direct calorimetric method. These thermodynamic data are discussed and compared with those for the formation of the Ln(III)EDTA complexes. Contrary to current opinion it is concluded that all trivalent lanthanide aquoions have the same coordination number in dilute solution. However, in the series of the lanthanide EDTA complexes the coordination number changes between Sm and Tb. In this region, equilibria occur between two types of EDTA complexes with different numbers of coordinated water molecules: equation image The corresponding equilibrium constants could be evaluated. The coordination number changes also in many other Ln complexes along the lanthanide series, and similar equilibria occur.

O-bonded and S-bonded sulphinate complexes of iridium(I) and iridium(III). Ligand isomerisation accompanying change in co-ordination number

The four-co-ordinate iridium(I) compound, Ir(O2S-p-tolyl)(CO)(PPh3)2 has O-bonded sulphinate but uptake of carbon monoxide or dioxygen results in isomerisation to S-bonded sulphinate while addition of methyl iodide leaves the ligand O-bonded.

Zur Kristallchemie des sechsfach koordinierten Siliziums

On the crystal chemistry of six-coordinated silicon. From a comparison of the crystal structures of high-pressure potassium-feldspar K(Si₀,₇₅Al₀,₂₅)₄[vi]O₈, stishovit Si[vi]O₂, thaumasite Ca₃[Si (OH)]₆ (SO₄) (CO₃) • 12H₂O, two modifications of silicon diphosphate Si[vi]P₂O₇ and of pyri-diniumtris (o-phenylenedioxy)-siliconate [C₅H₅NH]₂ [(C₆H₄O₂)₃Si], it follows that the [SiO₄] polyhedron is a slightly distorted octahedron with average values of 1.78 Å for the Si-O distances and 2.52 Å for the O-O edges. The tendency for silicon in phases with composition mSiX[p] • nAR[q] to coordinate itself with six oxygen atoms increases with increasing electronegativity (i. e. increasing acidity) of the elements X and A. In the same direction the pressure, which is necessary for the change [SiO₄] -> [SiO₆] decreases. While the covalency of the Si-O bond increases with increasing pressure up to the change of coordination number of silicon, a suddon drop in this covalency should occur at this change.

The co-ordination number of transition-metal ions. Part VII. An evaluation of steric factors in the stabilisation of high-spin five-co-ordinate nickel(II) complexes of multidendate α-pyridyl ligands

Nickel(II) complexes of six new potentially ter- or tetra-dendate α-pyridyl-containing ligands are described. Co-ordination number is assigned on the basis of the physical properties of solids and solutions. Both five- and six-co-ordinate compounds are characterised. The five-co-ordinate compounds, which are all high-spin, are of two kinds, (i) neutral mononuclear complexes containing the N3X2(X = halide) set of donor atoms, and (ii) uniunivalent salts in which the complex cation contains the N4X donor set. It is shown that the potentially tetradendate ligands may function either in a terdendate or in a tetradendate fashion, and a useful i.r. spectral criterion for unco-ordinated pyridyl groups is described. The change in co-ordination number from six to five accompanies a progressive increase in the steric demands of the ligands; in several instances five- and six-co-ordinate complexes co-exist in equilibrium in solution. It is shown that steric effects constitute a major basis, though not a sufficient one, for the stabilisation of the high-spin five-co-ordinate configuration for nickel(II). The polarisability of the anionic ligand is an important associated factor.

EPR Spectra of Mn2+in Chloride, Bromide, and Iodide Host Compounds

The EPR spectra have been obtained for Mn2+ fourfold coordinated in Cs2ZnCl4, K2ZnCl4, K2HgCl4, K2ZnBr4, and K2ZnI4; sixfold coordinated in NaCl, and KCl; and eightfold coordinated in CsCl. Large distortions from cubic symmetry were observed in CsCl. Variations in the manganese nuclear hyperfine splitting are discussed in terms of the nature of the ligand, changes in the manganese–ligand separation, and changes in the manganese coordination number. The effects of the changes in the coordination number have not been determined previously because concomitant changes in the internuclear distance usually have an opposite, and frequently larger, effect.

Luminescence and the cation coordination number in phosphate systems

The emission of Mn ++ in Zn 2P 2O 7 under X-ray excitation has been studied as a function of temperature. Although the cations undergo changes in coordination number across the phase transformation comparable changes do not occur in the emission wavelength. The results of experiments on MO:P 2O 5 systems related to the hypothesis of a relationship between the emission wavelength and the coordination number at the Mn ++ site are discussed. In these systems, the generalization that this site is a cation site and therefore that the luminescence color of Mn ++ determines the cation coordination is not true often enough to be useful.

Stress Build-up in Various Commercial Glasses by Ultra-Violet Irradiation

Stress build-up in a borosilicate and a 96% silica glass by ultra-violet irradiation was reported by the authors (J. Ceram. Assoc. Japan, 72 [11-1] 193-97 (1964)). As a preliminary study to throw light upon the mechanism of stress build-up, effect of ultra-violet irradiation on various commercial glasses was examined. After irradiation by 400W mercury discharge lamp for 500 and 1000 hours, glass test pieces were checked up photo-elastically, and if existed, stress at surfaces and depth of stressed layers were measured. Stress release by heat treatment was also investigated. Results were as follows:1. Stress build-up was observed only in borosilicate glasses. 2. In borosilicate glasses containing PbO or ZnO, stress was very small or unrecognized. 3. Stress increased with irradiation time. 4. When heated, stress began to release at about 250°C, faded away perfectly at 470°C and did not reappear on cooling. 5. In glasses containing no boron, stress did not come out by irradiation.From the results described above, stress build-up seemed to originate from special behaviour of boron atom (change of coordination number and of compactness of network structure of glass) under the action of ultraviolet ray. Obstruction effects of PhO or ZnO is a problem to be studied further.

A spectroscopic criterion for the coordination of aluminum in the anionic body

1. The oscillation frequency of the Al-O bond in the lattice of oxides and hydroxides of aluminum, built of AlO6 octahedra, lies at about 760 cm−1 in the infrared absorption spectra of these compounds. In the spectra of the monoaluminates of alkali and alkaline earth metals, built of AlO4 tetrahedra, the frequency of Al-O occurs in the region 800–900 cm−1. 2. We have studied the polymorphic transformation of the low temperatue and high temperature modifications of lithium monoaluminate, LiAlO2, which involves reconstruction of the lattice with change in the coordination number of aluminum with respect to oxygen from 6 to 4. The Al-O frequency in the spectrum ofl-LiAlO2 lies at 760 cm−1, and in the spectrum of h-LiAlO2 it lies in the region 800–900 cm−1.

Thermodynamic properties of transition metal compounds and coordination complexes: II. The lattice energies of some compounds of the divalent metals Ca ‐ Zn

AbstractThe lattice energies U of octahedrally coordinated Ca ‐ Zn compounds can be represented by an equation‐ U = C + I ‐ neΔwhere C is a constant, I the ionization potential (I1 + I2) of the atom and Δ another constant that is numerically comparable to the spectroscopic ligandfield splitting factor while ne is the number of 3d electrons in eg antibonding orbitals. It is shown that deviations from the predictions of this equation can be explained by changes in coordination number or the occurrence of cation‐cation bonding. The correlation can be derived from the m.o. theory in a simple manner provided that the lattice energy of compounds of inert‐gas ions is linearly dependent on I.

Vapor Pressures of the Neon Isotopes

The ratio of the vapor pressures of Ne20 and Ne22 have been measured in the temperature range 16–30°K. An accuracy of about 1% in the logarithm of the vapor-pressure ratio has been achieved. The latter is checked by comparisons of (1) triple-point pressures, (2) equilibrium fractionation experiments, and (3) the entropy difference of the condensed phases with thermal measurements. The Debye temperature for the solid derived from the ratio of the vapor pressures, 74.6°K, is in good agreement with values derived from the Debye-Waller temperature factor and theoretical calculations by Bernardes. The discrepancy between the characteristic temperatures derived from measurements of free energy with those from heat capacities is attributed to the role of the anharmonicity of the lattice. It is shown that the difference in the thermodynamic properties of solid and liquid neon in the vicinity of the triple point can be attributed to the change in coordination number.