Coordination lattice seven

Increasing the temperature results in the formation of B-type structures at least for some rare earth metal atoms. In this structure (SG C2/m) some of the metal atoms are seven coordinated by oxygen atoms others are still in distorted octahedral environment. The metal atoms are seen to be approximately hep (hexagonal closed packed). The coordination polyhedra for the anions are octahedra and half octahedra, tetrahedra and trigonal bipyramids. The relation to the A-typ structure formed at even higher temperatures is very close. Only small shifts in the oxygen sublattice are necessary to transform the B-type structure into the A-type structure (SG P32/m). The cation array is now perfect hep and alternal layers of tetrahedral and octahedral sites are then filled with anions (see Fig. 3-16). All metal atoms are seven coordinated. Lattice constants and bond distances... 

Coordination number seven is found in [Y(bzac)3(H20)] (Cotton and Legzdins, 1968). The coordination polyhedron is a distorted monocapped octahedron (with ideafized symmetry). In the seven-coordinate complex [Lu(thd)3(3-pic)], the coordination polyhedron is a monocapped trigonal prism (Wasson et al., 1973). The idealized syrmnetiy of such a coordination polyhedron is C2v The monocapped trigonal prism is also found in the crystal stmctures of, for instance, [Yb(acac)3(H20)] (Cunningham et al., 1969), [Lu(fod)3(H20)] (Boeyens and de Villiers, 1971), [Dy(thd)3(H20)] (Erasmus and Boeyens, 1971) and [Y(thd)3(H20)] (Gleizes et al., 1993). An example of a rare-earth /3-diketonate complex with a non-coordinated poly dentate ligand besides the above mentioned [Eu(thd)3(terpy)] complex, is [Eu(hfac)3(bipy)(H20)] (Thompson et al., 2002). In the latter compound, a non-coordinated 2,2 -bipyridine molecule is located in the crystal lattice and disordered over two positions. Examples of crystal stmctures of eight-coordinate rare-earth /3-diketonate complexes are... 

Salts of hexafluorovanadate can be obtained by high temperature techniques or from solutions containing hydrofluoric acid. For instance, X-ray patterns and DTA were used for the characterization of 17 double fluorides obtained by solid state reactions in the systems VF3 + MF (M = Li, Na, K, Rb, Cs, Tl) and seven double fluorides in the systems VF3 + MF2 (M = Ca, Sr, Ba, Pb),296 and the lattice constants297,29s and magnetic properties298 of A2B[VF6] (A, B = Cs, Rb, Tl, K, Na, Li) were also reported. The structure of the high temperature j0 phase of Li3VF6 has been determined and compared with the cryolite-type stable a form. The vanadium atoms have an octahedral coordination.299... 

In the structures of compounds of the type M3UF7 the seven F atoms are statistically distributed over fluorite lattice sites.153 The nine-coordinate thorium atom in (NH ThFg is surrounded by a distorted tricapped trigonal prismatic array of fluorine atoms, with the prisms sharing edges to form chains, whereas the uranium(IV) compound contains discrete dodeca-hedrally coordinated [UF8]4 ions. The protactinium(IV), neptunium(IV) and plutonium(IV) analogues are isostructural with the uranium compound.154... 

Fujiwara and Yamamoto have studied the racemization of anhydrous compounds of the type [M(phen)3]X2 and [M(bipy)3]X2 where M = Fe or Ni and X = Cl-, Br-, I- or C104-.26 The rates of racemization of the nickel compounds were found to depend on the identity of the anion racemization rates for the iron compounds were anion-independent. However, the kinetic analysis has been called into question.27 28 If valid, the kinetic anion effect for the nickel compounds follows an order that is opposite that found by Kutal and Bailar23 for the racemization of [Co(en)3]X3 salts C104 < I- < Br- < Cl . It was proposed25 that the iron compounds racemize by a twist mechanism and that the nickel compounds racemize by nucleophilic attack by lattice anions to form a seven-coordinate transition state. 

Au/ZrC>2 catalysts are less active than Au/TiC>2 catalysts, whatever method of preparation is used deposition of colloidal gold,83,91 DP12 or laser vaporisation.70 Activity depends on the method used (Table 6.12), and appears to be due only to the presence of Au°. The reason for the difference between zirconia and titania is not understood Zr4+ is more difficult to reduce than Ti4+, so anion defects may be harder to form. The lattice structures also differ in monoclinic zirconia (baddleyite) the Zr4+ ion is unusually seven coordinate, and phase transitions into tetragonal and cubic structures occur at >1370 and >2570 K, respectively. However, the... 

Reference to Table 7.26 shows the dysprosium diacetyl monoxime complex to have seven molecules of water. This complex loses two molecules of lattice water at 160°C. At 230°C, the remaining five coordinated water molecules are lost from the complex. 

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