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Structures and Reactions in Molten Salts.

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pend on the coordination number, the symmetry of the coordination polyhedron, and on the distances between the
coloring cation and the coordinating ligands.
To investigate this problem experimentally, oxides (MgO,
ZnO, spinels, MgTiO3, or silicates) were used as host lattices.
It was found that reduction of the coordination number from
6 to 4 causes a red-shift of the main absorption bands. The
same effect is observed if the coloring cation is incorporated
in a simple host lattice with only one type of cationic lattice
site and the lattice is expanded by isomorphous exchange of
larger cations [e.g. Nio.01 Mg0.99Ti03 (ilmenite lattice,
yellow) j . Ni0.01Cd099Ti03 (ilmenite lattice, red)]. A
bathochromic shift is observed with more complicated lattices
only when the isomorphous exchange of larger cations expands the coordination polyhedra containing the coloring
cation; this is not always the case. Reduction of the point
symmetry in the environment of the coloring cation does not
produce any significant bathochromic shift. Since the transition from Nio.1 Mg0.903 (regular octahedral coordination)
to Nio.1 Mgo.gTi03 (hexagonally distorted coordination
octahedron) results in a large red shift of all three main
absorption bands, it was at first concluded that this effect was
occasioned by the distortion of the coordination polyhedron.
However, further studies on phases of the perovskite type
revealed that the bathochromic shift of the bands required the
presence of both low-charged cations and high-charged
cations on coordinatively equivalent lattice sites. This results
in a weakening of the field around the low-charged coloring
cations.
These findings can be applied conversely in practice by using
light absorption to determine unknown types of coordination
and to study localized effects in crystal lattices which cannot
be investigated by other methods, e.g. X-ray techniques.
Apart from uses in crystalIography (e.g. mixed crystal formation), the changes in the light absorption can also be
applied to examine changes in bonding types between coloring
cation and coordinated ions or atoms.
[GDCh-Ortsverband Dusseldorf, Dusseldorf (Germany),
April 12th, 19651
[VB 9261237 IE]
German version: Angew. Chem. 77, 872 (1965)
Advances in Complexometry
R. Pribil, Prague (Czechoslovakia)
Complexometric titrations can be made selective by masking
interfering ions. Thus some colored cations can be converted to colorless or almost colorless complexes, e.g. Fe3@
with triethanolamine, Cu2@ with thioglycollic acid, Mn3@
with cyanide, and C030 with triethanolamine or cyanide.
Zn2@ and Cd2@ can be estimated in admixture using pmercaptopropionic acid.
Triethylenetetraminehexaacetic acid is a new complexometric titrating agent which forms 1:2 complexes MzY with
bivalent metals M such as Ga, Pb, Cd, or Zn and 1 : 1 com-
plexes MY with tri- and tetravalent metals. This reagent is
used for analysis of gallium/indium mixtures, etc. It can
also be used to determine thorium in mixtures with rare
earths, or thorium alongside scandium. Analyses of mixtures
of rare earths (RE) can be carried out using the following
displacement reaction :
[RE-EDTAIze f Zn2@ f PO438 + REP04 + [Zn-EDTAIzQ
Only La, Ce, Nd, and Pr are precipitated as their phosphates.
Holmium and the higher rare earths remain in solution and
are titrated complexometrically.
[GDCh-Ortsverband Nordbayern, Erlangen (Germany),
May 14th, 19651
[VB 931/234 IE]
German version: Angew. Chem. 77.871 (1965)
Structures and Reactions in Molten Salts
W. Bues, Tubingen (Germany)
BOjQ ions with D3h symmetry can be detected in molten
Li3BO3 by Raman spectroscopy. Melts with the composition
Li4Bz05 contain B20:e ions (Czv) plus BO:@ and B3O:Q
ions. This means that BzOlQ disproportionates by an electron donor-acceptor mechanism to give BOiQ and BOT.
The BO; ion is short-lived and reacts further in the melt
either with BO:Q to give Bz0tQor with BzO;Q to give B3O:O;
since the oxygen atoms in BO!@ and B20ZQ are of equal
basicity, the BO: reacts non-selectively. The BO!Q ion can
also be detected in melts of LisB307 and Li&O9. The
spectra of metaborates, borax, and diboron trioxide can be
readily interpreted starting from the short-chained anions:
in melts, boron has always the coordination number three.
This explains for example the great difference in density between B203 in the molten and crystalline states; in crystals
BzO3 has the coordination number four.
Molten ZnClz, like crystalline ZnC12, has a space lattice
structure with the coordination number four for the zinc.
KzZnCI4 melts consist of isolated ZnC14 tetrahedra, while
KZnCI3 melts contain chains of ZnC14 tetrahedra. Molten
mixtures of KNO3 and ZnCIz contain the ions NO:, ZnC1i0,
and Znza.
The TIC1 in molten mixtures of TIC1 and CuC12 can be
oxidized to TIC13 with HCI and oxygen. The TICI/TICI3/
CuCI/CuC12 melt catalyses the chlorination of ethylene to 1,2dichloroethane. At 280 "C and ratios of oxygen: HCI:
ethylene of 1:4:2, 3:8:4, and 1:2:1, the purity of the 1,2dichloroethane obtained is 99.0, 99.0, and 98.0 %, and the
conversion (based on the ethylene) is 26.5, 55.7, and 98.6 %,
respectively. A glass tube 80 cm long and 2 cm in diameter
with a sealed-in Grade 4 sintered-glass filter can be used to
achieve 30 seconds contact time of the gases with 150 g of the
melt, which foams intensely.
[GDCh-Ortsverband Giessen (Germany), June 14th, 19651
[VB 939/244 IE]
German version: Angew. Chem. 77, 871 (1965)
SELECTED ABSTRACTS
The structure of fluorenyl-lithium has studied by J. A . Dixon,
P. A . Gwinner, and D . C. Lini by NMR spectroscopy. When
heptane was added to the solutions formed by treating fluorene in tetrahydrofuran (THF) and dimethoxyethane (DME)
with lithium, a precipitate of solvated fluorenyl-lithium is
formed which does not release its solvent of crystallization
even after 48 h at pressure below 1 mm. Solutions of the complexes in perdeuterobenzene give NMR spectra whose integrated signals indicate the compositions RLi.3THF and
RU-1DME (R = 9-fluorenyl). The complexed T H F gives
signals at higher fields for both the a- and @-protonsthan free
Angew. Chem. internat. Edit.
I Vol. 4 (1965) f No. 10
THF. The relative positions of the methyl and methylene proton signals were interchanged in the complexed and free
forms. Because of the electron donor/electron acceptor interactions between the cation and the ether molecule, a shift to
lower fields would have been expected. The 7Li resonance
occured at higher field strengths (3 ppm for the T H F complex) than in aqueous solutions of inorganic lithium salts. It
was concluded that the solvated lithium cation lies above the
plane of the aromatic carbanion and thus falls within the
shielding range of the ring current. 1 J. Amer. chem. SOC.87,
[Rd 343/552 IE]
1379 (1965) / -Eb.
893
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