Transition metal fluorides

The crystal structures of many transition metal fluorides are well known. Such knowledge is necessary for the interpretation of absorption spectra, as it is obvious that the term splittings are strongly related to the surroundings of the metal ions. 

The structural properties of transition metal fluorides have been reviewed, e.g. by Babel (2). If electronic transition energies are considered, however, one need not look at the total variety of structure tjq es,but only at the nearest neighbomrs of a transition metal ion. As a first approximation, the unit [Me + seems to behave like an isolated cluster , even 

The transition metal ions in fluorocomplexes are generally six-coordinated with an octahedral arrangement of the fluoride ions. The regular coordination predominates, but sometimes there appear distinct 

however, odvious that compounds with an octahedral Ej ground state practically always appear in at least tetragonally distorted octahedra, decause the a-antibonding eg orbitals are occupied by one or three electrons. The interaction between the electronic state an dthe eg vibrational mode (the only one which is JT active) therefore results in a considerable energy gain for the D4 symmetry compared with the 0 symmetry, so that the energy minimum is manifested in a static distortion. 

if-Otbital Energy Differences in a Tetragonal Ligand Field 

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Absorption spectra and ligand field parameters of tetragonal 3[Pg.36]

Transition metal fluorides and their complexes. A. G. Sharpe, Adv. Fluorine Chem., 1960,1,29-67 (251). 

Oelkrug D (1971) Absorption Spectra and Ligand Field Parameters of Tetragonal 3d-Transition Metal Fluorides. 9 1-26... 

Natural population analysis of transition-metal-fluoride wavefunctions gives orbital populations that are generally consistent with the expected configurations, but with large departures from an idealized ionic picture. Table 2.4 compares the... 

Figure 4.29 Optimized geometries of saturated group 6-11 third series transition-metal fluorides MF (see Table 4.18).

IV, A. Rittner s electrostatic model has been applied to the dissociation of metal halides (5) and Kapustinskii s equation to transition metal fluorides (26). A rough correlation between enthalpies of fluorides and the corresponding oxides and chlorides is suggested (22). 

Borides The electrolysis (at 950-1100°C) of a mixture of a borate and a transition metal fluoride (or alkaline-earth fluoride with the transition metal oxide) resulted in the synthesis of several borides (Ca, Sr, Y, Th, Ti, V, etc.). 

S.Fabbrici, E.Montanaii, G.Calestani and A. Migliori Charge ordering and tilt modulation in multiferroic KxM"xM "i xF3 (0.4tetragonal tungsten bronze structure Chem. Mater. 2004 16(16) 3007-3019... 

The structural information we have of pentafluorides in the solid state is relatively new. The similar melting points (near 100° C and below) and even more so the almost identical boiling points (close to 230°) of the transition metal fluorides MeFs point to similar structures of these compounds. Their high volatility is clearly less than that of the hexafluorides so that one may assume associated aggregates or polymere molecules in the solid state. New structure analyses showed this assumption to be true. There exist at least three structure types within the 12 pentafluorides of d-transition elements hitherto known. Two crystal... 

Ternary transition metal fluorides of the TlAlF4-t37pe seem to exist in NH4SCF4 [124), in RbCrF4 and RbFeF4 [8). The two Rb-compounds mentioned, however, possibly crystallize in a superstructure of the TlAlF4-type. The lattice constants of the unimolecular unit cells are listet in Table 20 together with some further isostructural Al-compounds (52). 

On the other hand von Schnering and Bleckmann [300) recently reported the first ternary transition metal fluorides crystallizing in a normal... 

This type usually called K2NiF4-structure 15) was investigated for the first time by Winkler and Brehler 337) at (KaMgF4). During the last years many oxides and fluorides of this type have been reported. Meanwhile isostructural transition metal fluorides containing the larger A-ions K, Rb, Cs, NH4 and T1 are known. 

The following discussion is restricted to such structural elements already observed in transition metal fluorides, whereas others, examples of which are not known yet, were omitted. Later on influences will be described that may affect crystal structures by means of size, charge, electronic configuration and bonding of the constituent ions of a compound. 

In the following chapter some special magnetic properties of the transition metal fluorides will be dealt with, which depend more clearly upon a specific bonding behaviour in and between the MeFe-octahedra than the crystal structure itself. 

VIII. Magnetic Interactions and Magnetic Structures in Transition Metal Fluorides... 

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