Tetragonal compression

The limitations of the simple Zintl-Klemm concept can be illustrated by differences in the two [MT1] intermetallics (M = Na [79] and Cs [80]). Complete electron transfer from M to T1 leads to [ M TI, where the Tl anion with four valence electrons is isoelectronic with a neutral group 14 atom and four bonds and needed to attain the octet configuration. Hence, the Tl- anion should form structures similar to allotropes of carbon or heavier group 14 elements. Indeed, [NaTl] has a stuffed diamond structure [79] with internal Na and an anionic (Tl-) lattice similar to diamond. However, the Tl- anions in [CsTl] form tetragonally compressed octahedra [80] unlike any structures of the allotropes of carbon or its heavier congeners. 

The structure of these compounds was elucidated by the work of Okazaki and Suemune (236) on the fluoride KCuFj. The unimolecular tetragonally compressed perovskite cells of previous reports (90) do not account for additional reflections observed in single crystal work. Instead one has to conceive a unit cell containing z = A formula units... 

The only example of a tetragonal compressed octahedron, theoretically predicted as well (212, 214), seemed to be represented by the... 

The salts KCrF3 and RbCrF3 have distorted perovskite structures, and from analysis of powder data the former contains tetragonally compressed CrFe octahedra in which two Cr—F bond distances are 2.00 A and four 2.14 A.244 The ionic radius of Cr23- in fluoride perovskites has been estimated at 0.73 A as a weighted average from lattice constants.245... 

Later work9 10 suggests that the tetragonally compressed structure is unlikely. f For ACrXj and A2Crl6 see Table 36. 

Elongated tetragonal Compressed tetragonal Elongated rhombic Compressed rhombic ... 

Crystals of Cs CuCU contain nominally tetrahedral CuClf" ions, shown by x-ray crystallographic analysis to have the tetragonally compressed approximate Dld symmetry (Fig. 5a). It is likely, therefore, that the orbitals containing the z label are stabilized with respect to the tetrahedral energies, as shown in Fig. 5b, and given rise to a 2B2 ground term. 

Tetragonally compressed Octahedral Tetragonally elongated Square planar ... 

Fig. 1. The splitting of the d orbitals in tetragonally compressed, tetragonally elongated, and square planar geometric for a d1 ion and the resulting relative g values for d7 and d9 configurations.

The sexidentate amino acid edta4- forms a high-spin nickel(II) complex which can be oxidized to a tetragonally compressed nickel(III)... 

It is clear that the A1203 support contributes to the stability of Mo5+. Various authors have attributed the Mo5+ to different species. Some of the proposed species are shown in Table V. The H-containing species are particularly attractive in view of the irreversible H] found on these reduced catalysts. Asmolov and Krylov (44) consider Mo5+ to be in a tetragonally compressed C4v complex. Abdo and co-workers (45) have recently proposed the structure... 

Fig. 16 Energy levels (not to scale, values in cm 1) for a Ti(III) complex on tetragonal compression (left direction) and elongation (right direction)...

X- and Q-band EPR in the temperature range 4.2-300 K were used to obtain data for the Cu(H20)g+ JT complex. The cases of the JT complexes in a site of cubic (or trigonal) symmetry (a), tetragonal elongated symmetry (b), and tetragonal compressed symmetry (c) are analyzed. The crystallo-hydrates are suitable and convenient objects for investigation, as representatives of this class of compounds ... 

Tetragonal compression around the central Cu2+ ion is much rarer K2CuF4 is an example with two shorter and four longer Cu-F distances, viz., 1.95 vs. 2.08 A [71],... 

They are all diamagnetic, and this can be attributed to the large tetragonal compression of the octahedron by the trans 0=0s bonds causing the two d electrons to pair up in the dxy orbital (assuming the oxo ligands to lie on the z axis).464... 

The bromide system is similar but there is only indirect evidence for VI4 in the vapor phase. VF4 is polymeric with layers of comer-sharing tetragonally compressed VF6 moieties.1 The trihalides have the Bil3 structure in which each metal atom is at the center of a nearly perfect octahedron of halogen atoms. 

The complex Mn(acac)3 has two forms, one of which shows a substantial tetragonal elongation (two Mn—O = 2.12 A four Mn—O = 1.93 A) as do other high-spin complexes such as porphyrin adducts the other form shows a moderate tetragonal compression (two Mn—O = 1.95 A four Mn—O = 2.00 A). 

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