Tetrahedral ions

Manganaies(Vf), (Mn04) . Deep green tetrahedral ion (Mn02 plus fused K.OH with KNO3, air, etc.). Only stable in basic solution. 

They probably all contain the tetrahedral ion [Li(OPPh3)4]+ which was established by X-ray crystallography for the compound Lil.SPhsPO the fifth molecule of PhaPO is uncoordinated. 

The T ground term of the tetrahedral ion is expected to lead to a temperature-dependent orbital contribution to the magnetic moment, whereas the A ground term of the octahedral ion is not, though mixing of the excited T2g(F) term into the AigiF) ground term is expected to raise its moment to ... 

The Spectra and Electronic Structure of the Tetrahedral Ions Mn04, Cr04 and C104 ... 

The +6 state of chromium is represented by the chromates and dichromates. The chromate ion is a tetrahedral ion with Cr at the center dichromate ion may be visualized as two such tetrahedra having one oxygen corner in common. Figure 22-9 shows the arrangements. Chromates can easily be converted to dichromates by addition of acid,... 

Fluoride forms a tetrahedral ion with aluminum, AIF4, which forms a complex with the GDP -a (3 y form of heterotrimeric G-proteins. In the case of Gs, the complex AIF4 -GDP -a s(3 y behaves much as GTP or the more stable GTP derivatives, GTPy S or GPP(NH)P,... 

In each case, the N atom is sp hybridized, with one lone pair of electrons and three o-bonds. A quaternary ammonium ion is a tetrahedral ion of the form R4N, where as many as three of the R groups (which may all be different) can be replaced by H atoms. For example, the tetramethylammonium ion, (CH3)4N+, and the trimethylammonium ion, (CH3)3NH+, are quaternary ammonium ions. The amino group, the parent functional group of amines, is —NH2. 

LFSE s for tetrahedral species are computed in a similar manner. They are compared with the results for octahedral systems in Fig. 8-7. No illustration of LFSE s for low-spin tetrahedral ions is included here because, as noted in Chapter 5, the much smaller values of Aet relative to oct ensures that pairing energies P always outweigh the ligand-field terms in practice. 

One might be tempted to bring some structural features of the phosphate ion in line with those of the glucose acceptors represented in XVI and XVIII. Thus, in the tetrahedral ion... 

K4Ge4, can be described as a polyanionic compound (as a Zintl phase also) containing the ion Ge44. This tetrahedral ion can be considered a naked (that is without any ligands bounded to the vertices) tetrahedral cluster formed by a main group element (that is Ee = 5 3 = 5X4 = 20). The electron count, on the basis of the Ge valence electrons and of the ion charge results in Ee = 4 X 4 + 4 = 20. 

To illustrate the effect of geometry on the Cl shift. Table IV shows some data for several pairs of high spin tetrahedral and octahedral iron complex ions. In each case the shift of tetrahedral ion is more negative than that of the octahedral ion, and the difference in shift is rather substantial. We feel that in these cases the differences in shifts can be ascribed to differences in 4 covalency six electronegative ligands are more able to draw off 5 electron density than are four. Apparently it makes little difference whether the six ligands belong exclusively to a... 

The green tetrahedral ion MnO " is stable in basic solution. It can be prepared by reducing MnOj with Fe(CN)g . There is uncertainty about the MnO "—H2O exchange rate. The ion disproportionates in acid and the kinetics have been studied by stopped-flow. At 610 nm where loss of MnO is monitored, the reaction is first-order. At 520 nm where formation of Mn04 is observed, the reaction is second-order. These observations and the H dependency suggest a mechanism... 

In NaAlSi303, because the ionic size of Na is much smaller than that of K+, reticular distortion is implicit in the structure for simple topologic reasons, and migration of tetrahedral ions is energetically easier, not implying symmetry... 

Type IV spectra are found with the tetrahedral ions such as permanganate and chromate. 

For tetrahedral ions or molecules of the type XY , where X is a transition metal the vi(Fz)fvz(E) frequency ratio changes from a value of less than one to a value greater than one with the increasing mass ratio MxfMy. 

The most stable state of nitrogen in acidic solution is the ammonium ion, NH4(aq), which is isoelectronic with CH4 and H30+. It is a tetrahedral ion with strong N-H bonds. The mean N-H bond enthalpy in NH4(aq) is 506 kJ mol 1 (that of the O-H bonds in H30 + is 539 kJ mol" ). The enthalpy of hydration of the ammonium ion is — 345 kJ mol V This value placed into the Born equation (3.32) gives an estimate of the radius of the ammonium ion of 135 pm, a value insignificantly different from its thermochemical radius of 136 pm. The value is comparable to that estimated for the smaller H30+ ion (99 pm) from its more negative enthalpy of hydration (— 420 kJ mol -see Section 2.6.1). The proton affinity of the ammonia molecule is of interest in a comparison of its properties with those of the water molecule. The proton affinity is defined as the standard enthalpy change for the reaction ... 

Table 6.12 Fundamental vibrational frequencies for frequencies are given as wavenumbers with units of cm some tetrahedral ions the...

Hall, M. B. 2000. Perspective on The Spectra and Electronic Structure of the Tetrahedral Ions Mn04 , CrO4 , and C1O4 Theor. Chem. Acc., 103, 221. 

The observed values of interatomic distances in the tetrahedral ions of the ortho oxygen acids of the second-row elements are given in Table 9-2. They are 0J5 to 0.19 A leas than the values calculated for the single-bond lengths with the covalent radii and the correction for... 

Glassy solutions of ZnX2 (X = halide) in water have also been studied by Raman spectroscopy and the results indicate the presence of the tetrahedral ions, [ZnX (H20)n](Z-n) .624 625... 

The tetrahedral ions, POtHSOr and CIO - show no near ultraviolet absorption whereas the ions, XO4", of the fourth-row transition elements, which have the same number of valence electrons, show characteristic visible and near ultraviolet absorption, two strong maxima with the corresponding peaks displaced toward shorter wavelengths with decreasing atomic number of the central atom. This trend is also observed for the fifth- and sixth-row transition element compounds. A satisfactory theory must account for these differences and regularities. 

This region of the spectrum for MnOf dissolved in anhydrous NaClO is shown in Fig. 4. The site symmetry of the tetrahedral ions in this lattice is CW- The degenerate levels should be completely split in this symmetry, the symmetries Of the resulting states (in CV) and the polarization of the transitions rendered allowed by the perturbation are given in Table V. As indicated in this table a T state in a field of symmetry Ctv should show absorption with electric vector parallel to the b and c axes, for an E state absorption with electric vector parallel to the a axis, the direction of the twofold axis at position of the ion. The spectrum in the region II (Teltow s designation) corresponds precisely to what one would expect from a T state. ... 

Not very many solid-solution studies were reported, mainly because all the easy substituted ions have been previously experimentally treated. The tetrahedral ions continue to be studied, and BD4 in alkali halides was studied by Coker and Hofer 172) see also Heyns, Schutte and Scheuermann 2,4>. The solid solutions were prepared by diffusing the deuteride into optical grade crystals, and the IR spectra were recorded at 90 °K, yielding all 24 vibrational bands of BH4, BH3D, BH2D2, BD3H and BD4. The trends are similar to those first found by Schutte and Ketelaar for BH4 solid solutions 173>. There is still no satisfactory theory for the spectra of ions in solid solutions, but Metselaar, 74) gave a theory of lattice vibrations of solid solutions in his thesis on the N03 ions in alkali halides. 

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