Polyanion Condensation in Inorganic and Hybrid Fluoridometallates (IV) of Octahedrally Coordinated Ti, Zr, Hf, V, Cr, W, Mn, Ge, Sn, and Pb

In fluorides, the M4+ cations of M = Ti, V, Cr, Mn, Ge, Sn, and Pb favour the octahedral coordination of six F ligands. Some examples of M4+ with larger cations (M = Zr, Hf, W) in octahedral coordination are also known. If not enough F ligands are available to have isolated MIVF6 octahedra, they must share their F ligands. The crystal structures of such fluoride metalates (IV) show the variety of possible structural motifs of the zero-dimensional oligomeric anions [M2F11]3− (M = Ti, Cr), [M3F15]3− (M = Zr, Hf), [M3F16]4− (M = Ge), [M4F18]2− (M = Ti, W), [M4F19]3− (M = Ti), [M4F20]4− (M = Ti), [M5F23]3− (M = Ti), [M6F27]3− (M = Ti), [M6F28]4− (M = Ti), [M8F36]4− (M = Ti, Mn), [M10F45]5− (M = Ti) to one-dimensional chains ([MF5]−)∞ (M = V, Ti, Cr, Ge, Sn, Pb), double chains ([M2F9]−)∞ (M = Ti, Mn), columns ([M3F13]−)∞ (M = Ti), ([M4F19]3−)∞ (M = Ti), ([M7F30]2−)∞ (M = Ti), ([M9F38]2−)∞) (M = Ti), two-dimensional layers ([M2F9]−)∞ (M = Cr), ([M8F33]−)∞ (M = Ti), and three-dimensional ([M6F27]3−)∞ (M = Ti) architectures. A discrete monomeric [M2F9]− anion with two MIVF6 octahedra sharing a common face has not yet been experimentally demonstrated, while two examples containing discrete dimeric [M2F10]2− anions (M = Ti) with two MIVF6 octahedra sharing an edge are still in question.


Introduction
In the structural chemistry of inorganic and hybrid (with organic cation and inorganic anion) fluorine compounds, the coordination number six with an octahedral coordination of the metal atom (M) of the anion by six fluorine ligands is preferred for almost all transition elements and for some main group elements [1,2].Exceptions are metal cations of heavier elements, which prefer a higher coordination than six, and metal cations with the electron configurations d 8 and d 9 , which often occur in square-planar coordination.In the fluorides, condensation of MF 6 octahedra is favoured over the apexes, in contrast to the higher halogen homologues, where associations over the edges or faces are more common [3].
When the number of F ligands per M IV cation is less than six, the M IV F 6 octahedra must share their F ligands instead of being isolated.The usual term for such shared F atoms is a bridging fluorine atom (F b ), i.e., the fluorine atom connects two metal centres of the anion.The term terminal fluorine atom (F t ) is used for the remaining fluorine atoms that are not involved in such bridging.
The crystal structures of fluoride metallates (IV) with linked M IV F 6 octahedra show the variety of possible structural motifs, from oligomeric anions to chains and columns to layers and three-dimensional framework architectures of the anions.This paper summarizes known perfluoridometallate (IV) salts with different anions determined in the crystal structures of inorganic and hybrid fluoridometallates (IV) with M = Ti, Zr, Hf, V, Cr, W, Mn, Ge, Sn, and Pb.Only examples with octahedral coordination of the M(IV) centre are included.
Many new inorganic and hybrid fluoridometallate (IV) salts of octahedrally coordinated Ti, Zr, Hf, V, Cr, W, Mn, Ge, Sn, and Pb have been structurally characterized in the last two decades.They contain anions in different sizes and geometries.Some of them were prepared for the first time and have a unique geometry.The aim of this review was to collect all of these data in one place and provide researchers with useful information for further planning of the preparation of new inorganic and hybrid fluoridometallate (IV) salts with anions in the desired geometry.

Discrete Oligomeric Anions
2.1.[M 2 F 9 ] − Anion (M = Ti, Ge) 19 F NMR spectroscopy was used to detect the existence of the dimeric [Ti 2 F 9 ] − anion in liquid SO 2 solution [4].The [Ti 2 F 9 ] − anion has a face-linked bioctahedral structure (Figure 1).The "volume-based" thermodynamic approach suggests that cations larger than Cs + favour the formation of solid perfluoridotitanium (IV) salts with discrete dimeric [Ti 2 F 9 ] − anions [5].However, experiments have shown that an increase in the size of monocations does not favour the formation of [Ti 2 F 9 ] − over [Ti 4 F 18 ] 2− salts (containing discrete anions).Crystal structure determination of the [Me .Although a theoretical ab initio study revealed that the dimeric [M 2 F 9 ] − anions (M = T, Ge) are predicted to be electronically and thermodynamically stable systems [7], all attempts to isolate salts with such anions in the solid state have failed so far.
was to collect all of these data in one place and provide re information for further planning of the preparation of new i fluoridometallate (IV) salts with anions in the desired geometry.

[M 2 F 10 ] 2− Anion (M = Ti)
The M IV F 6 edge-sharing structure of the dimeric anion [Ti 2 F 10 ] 2− was proposed on the basis of the 19 F NMR data of the SO 2 solution of the di-n-propylammonium hexafluoridotitanate-TiF 4 system (Figure 2) [4].Later, two crystal structures were described.However, both are doubtful.The first report describes a [Ti 2 F 10 ] 2− salt of tetramethyltetrathiafulvalene (TMTTF), where the average charge of the single TMTTF cation was estimated to be +2/3, while the oxidation state of the titanium was assumed to be Ti 4+ [8].The second compound was originally formulated as a salt of the diprotonated piperazinium cation [C 4 H 12 N 2 ] 2 [Ti 2 F 10 ]•2H 2 O [9].In this case, the anion has a charge of −4, which corresponds to a Ti 3+ compound.Later, the formula was corrected by removing a hydrogen atom, resulting in a monoprotonated piperazinium cation [C 4 H 11 N 2 ] 2 [Ti 2 F 10 ]•2H 2 O [10].In the figures shown, however, diprotonated cations remained [10].The 3+ oxidation state is also indicated by the Jahn-Teller distortion of the octahedrally coordinated titanium atoms mentioned by the author.Therefore, the structure of the discrete dimeric [Ti 2 F 10 ] 2− anion is still limited to the reported DFT-optimised theoretical structure [11], while reliable experimental evidence is still pending.

[M2F11] 3− Anion (M = Ti, Cr)
A summary of the crystal data of the salts consisting of [M2F1 is given in Table 1.(10) 90 * The crystal structures were determined at the indicated temperatures.
In discrete [M2F11] 3− anions (M = Ti, Cr), two MF6 octahedra sh The distortion of the geometry of the [M2F11] units is usually des

[M 2 F 11 ] 3− Anion (M = Ti, Cr)
A summary of the crystal data of the salts consisting of [M 2 F 11 ] 3− anions (M = Ti, Cr) is given in Table 1.
In discrete [M 2 F 11 ] 3− anions (M = Ti, Cr), two MF 6 octahedra share a common vertex.The distortion of the geometry of the [M 2 F 11 ] units is usually described by the bridging angle α (bending of F 5 M-F b -MF 5 around the bridging fluorine F b ) and the torsion angle ψ (torsion of two planar MF 4,eq groups from the eclipsed to the staggered conformation).There are three crystallographically unique Ti 2 F 11 units in [ImH] 3 [Ti 2 F 11 ].Each of them has a different conformation (Figure 3) [12].In two of them, the equatorial TiF 4 -planes of the TiF 6 octahedra of [Ti 2 F 11 ] 3− are eclipsed and the Ti-F b -Ti angle is 180 • .In the third, the TiF 4 -planes of two TiF 6 octahedra are in gauche conformation with a dihedral angle of 8.50 (6) • and a slightly bent Ti-F b -Ti angle (174.28(18) • ) [12].In both, [ImH] ]•H 2 O, the Ti-F t bond lengths are comparable.They range from 1.768(3) to 1.908(2) Å for Ti-F t bonds and from 1.9683(5) to 1.9805 (6) Å for Ti-F b bond lengths [12,13].

[M3F15] 3− Anion (M = Zr, Hf)
A summary of the crystal data of the salt consisting of [M3F15] 3− ani given in Table 2.   2.  (7) 66.454 (13) * The crystal structure was determined at the indicated temperature.* The crystal structure was determined at the indicated temperature.
were used to determine the gas phase geometrie [Ti4F20] 4− anions, which was helpful in assigning the of the anion [12].[ImH]4[Ti4F20] [12].Quantum chemical calculations at the B3 were used to determine the gas phase geometries and vi [Ti4F20] 4− anions, which was helpful in assigning the experim of the anion [12].were used to determine the gas phase geometries and vib [Ti4F20] 4− anions, which was helpful in assigning the experime of the anion [12].7. The crystal structure of [ImH] 3 [Ti 5 F 23 ] (Im = imidazole) is the only example that contains a discrete pentameric [M 5 F 23 ] 3− anion (Figure 17) [12].It is built from five TiF 6 units, with four of the TiF 6 octahedra sharing two cis-vertices and forming a tetrameric ring as in [Ti 4 F 20 ] 4− , and the fifth TiF 6 unit sharing three fluorine vertices with three TiF 6 units of the tetrameric ring.The bond lengths of Ti-F t and Ti-F b are 1.757(3)-1.848(3)Å and 1.942(2)-2.014(2)Å, respectively [12].Quantum chemical calculations at the B3LYP/ SD-DALL level of theory were used to determine the gas phase geometries and vibrational frequencies of the [Ti 5 F 23 ] 3− anions, which were helpful in assigning the experimental vibrational frequencies [12].
les 2024, 29, x FOR PEER REVIEW

[M6F27] 3− Anion (M = Ti)
A summary of the crystal data of the salts consisting of [M6 given in Table 8.

[M 6 F 27 ] 3− Anion (M = Ti)
A summary of the crystal data of the salts consisting of [M 6 F 27 ] 3− anions (M = Ti) is given in Table 8.In C(NH 2 ) 3 ] 3 [Ti 6 F 27 ]•SO 2 , the [Ti 6 F 27 ] 3− anion consists of six TiF 6 octahedra (Figure 18) [22].Three TiF 6 octahedra form a trimeric ring by sharing cis-vertices.Two such rings are connected via the bridging fluorine atoms and form a trigonalprismatic geometry.In this way, all titanium atoms are coordinated with three F t and three F b atoms, which are located in the fac positions.The bond lengths of Ti-F t and Ti-F b are 1.754(1)-1.788(1)and 1.943(1)-2.010(1)Å, respectively [22].
The [Ti 6 F 27 ] 3− anion with the same geometry was also observed in the crystal structure of 18), where disordering of the imidazolium cations was observed and there were problems in determining additional cations providing the missing positive charge [22].It was assumed that [H 3 O] + cations were most likely present.
The [Ti6F27] 3− anion with the same geometry was also observed of [C3H5N2]2[H3O][Ti6F27] (Figure 18), where disordering of the im observed and there were problems in determining additional missing positive charge [22].It was assumed that [H3O] + cations w

[M6F28] 4− Anion (M = Ti)
In the study of the imidazole-TiF4-HF system, single crys [ImH]8−n[X]n[Ti8F36][Ti6F28] were grown [23].Its crystal structure perfluoridotitanate (IV) anion-cubic [Ti8F36] 4− octamers and a hex Unfortunately, it was not possible to accurately determine all structure, but the proposed models of the anions are well refined.a very unusual geometry (Figure 19).In the centre are two TiF6 vertex.Attached to this pair is a TiF6 unit that shares a fluorine octahedra.There is also a chain of three TiF6 octahedra in which end of the chain shares two vertices with two octahedra in the centr anion.Unfortunately, it was not possible to accurately determine all cations in the crystal structure, but the proposed models of the anions are well refined.The [Ti 6 F 28 ] 4− anion has a very unusual geometry (Figure 19).In the centre are two TiF 6 octahedra that share a vertex.Attached to this pair is a TiF 6 unit that shares a fluorine atom with each of the octahedra.There is also a chain of three TiF 6 octahedra in which each octahedron at the end of the chain shares two vertices with two octahedra in the centre of the [Ti 6 F 28 ] 4− anion.
a very unusual geometry (Figure 19).In the centre are two TiF6 octahed vertex.Attached to this pair is a TiF6 unit that shares a fluorine atom w octahedra.There is also a chain of three TiF6 octahedra in which each oc end of the chain shares two vertices with two octahedra in the centre of the

[M10F45] 5− Anion (M = Ti)
A summary of the crystal data of the salt consisting of given in Table 10.10.
A summary of the crystal data of the salts consi Ge, Cr) is given in Table 11.11.The crystal structure of XeF 5 GeF 5 is a rare case in which M IV F 6 octahedra share their F atoms in trans position to form infinite ([MF 5 ] − ) ∞ chain-like anions (Figure 23) [27].The coordination around each Ge atom is an elongated octahedron of fluorine atoms.The Ge-F b -Ge angle is equal to 140.70 (20) • [27].Viewed along the GeF 5 chain, all F t are in eclipsed positions.All Ge-F t distances within the square plane are equal at 1.745(2) Å, and the Ge-F b distance is 1.890(1) Å [27].The crystal structure of XeF5GeF5 is a rare case in which M IV F6 octahedra share F atoms in trans position to form infinite ([MF5] − )∞ chain-like anions (Figure 23) [27] coordination around each Ge atom is an elongated octahedron of fluorine atoms.Th Fb-Ge angle is equal to 140.70(20)° [27].Viewed along the GeF5 chain, all Ft are in ecl positions.All Ge-Ft distances within the square plane are equal at 1.745(2) Å, and th Fb distance is 1.890(1) Å [27].

Cis-([MF
There are many more examples of polymeric ([MF 5 ] − ) ∞ anions (M = Ti, V, Cr, Mn, Ge, Sn, Pb) in which MF 6 octahedra share F atoms in the cis position, especially in the case of titanium.The different tilting of the MF 6 octahedra in the chains leads to small differences in their geometry.A summary of the crystal data of the salts consisting of cis-([MF 5 ] − ) ∞ anions (M = Ti, V, Cr, Mn, Ge, Sn, Pb) is given in Table 12.H 3 OTiF 5 crystallizes in the monoclinic space group C2/c (Table 12) [29].The Ti-F b -Ti angle is 146.56 • (Figure 25) [29].
Ti-F bond lengths are typical for poly[perfluoridotitanate (IV)] co from 1.763(1) to 1.877(1) A and from 1.964(1) to 2.004(1) A for the T respectively [22].The Ti-Fb-Ti angles are 148.48(7) and 157.07( 7)° [2 The crystal structure of ClO2GeF5 consists of infinite ([GeF5] − )∞ c However, their geometry differs from the geometry of the ([GeF5] − )∞ [34], where the GeF6 octahedra also share common cis-vertices.The salt are crenelated and not linear as in the case of O2GeF5•HF.Th range from 1.73 Å to 1.78 Å and are shorter than the Ge−Fb bond leng The Ge−Fb−Ge angles are 148.1°and 143.4° [27].The crystal structure of ClO 2 GeF 5 consists of infinite ([GeF 5 ] − ) ∞ chains (Figure 41) [27].However, their geometry differs from the geometry of the ([GeF 5 ] − ) ∞ chains in O 2 GeF 5 •HF [34], where the GeF 6 octahedra also share common cis-vertices.The chains in the former salt are crenelated and not linear as in the case of O 2 GeF 5 •HF.The Ge-F t bond lengths range from

Cis-and Trans-([MF5] − )n Anions (M = Cr)
A summary of the crystal data of the salt consisting of cis-and trans-([MF5] − ) (M = Cr) is given in Table 13.The crystal structure of (XeF5CrF5)4•XeF4 consists of infinite chains of distort octahedra sharing alternating trans-and cis-vertices (Figure 42) and is the only e of its kind [28].Cr−Ft bond lengths range from 1.701(8) Å to 1.895(7) Å and Cr−
In  In [XeF5][Ti3F13], the anionic part consists of tetrameric Ti4F20 and units that share vertices and are alternatively connected to form ([ (Figure 54) [26]    The crystal structure of (O2)2 [Ti7F30] consists of column-like ([Ti7F30] 2− )∞ anions ( 56) [44].The structure of the ([Ti7F30] 2− )∞ anion is comprised of cubic units of eig octahedra, with two TiF6 units in opposite corners of the cube sharing vertice neighbouring cubes.In this way, the Ti atoms common to the neighbouring cub coordinated by six bridging fluorine atoms, while the other Ti atoms are coordina three Fb and three Ft atoms.The negative charge of the anions is compensated cations located between the ([Ti7F30] 2− )∞ columns.16.   16.The infinite two-dimensional (2-D) arrangement of poly[perfluoridometallate (IV)] anions is observed in the case of the ([Ti 8 F 33 ] − ) ∞ anion characterized in CsTi 8 F 33 [46]  In CsTi 8 F 33 , two Ti atoms are coordinated by three bridging and three terminal fluorine atoms, while the other two are coordinated by four bridging and two terminal fluorine atoms, ultimately leading to a 2-D framework (Figure 58) [46].

CsTi8F33
P31c          17.The ([Ti 6 F 27 ] 3− ) ∞ anion is a three-dimensional framework consisting of TiF 6 octahedra (Figure 61).Its structure can be described as composed of non-planar tetrameric Ti 4 F 20 units consisting of four octahedra, each sharing two cis-vertices.Each Ti 4 F 20 unit is connected to four other Ti 4 F 20 units so that each TiF 6 octahedron of a tetrameric ring is connected to another tetrameric unit.There are two types of channels in the crystal structure of the ([Ti 6 F 27 ] 3− ) ∞ anion.The channels are occupied by cations and probably also by molecules of the solvent.
[H3O]3 Slow decomposition in attempts to grow single crystals Rb4[Ti8F36]•6HF [24] led to the growth of cube-shaped crystals of the same type of anion ([Ti6F27] 3− )∞ was found in [H3O]3[Ti6F27] [31 three cases, there is a problem with charge balance, i.e., a deficit o salts, there is a possibility that some [H3O] + was present, leading to salts.
The ([Ti6F27] 3− )∞ anion is a three-dimensional framework cons (Figure 61).Its structure can be described as composed of non-p units consisting of four octahedra, each sharing two cis-vertic connected to four other Ti4F20 units so that each TiF6 octahedron connected to another tetrameric unit.There are two types of c structure of the ([Ti6F27] 3− )∞ anion.The channels are occupied by ca by molecules of the solvent.

Conclusions
On the basis of this review is possible to draw some conclus further direction of this work: Among the fluoridometallates (IV), the largest number of diff for Ti.This is not so surprising in view of the numerous studies tha in recent years [5][6][7]11,12,[14][15][16]19,[22][23][24]26,32].The use of som organic cations could still lead to new anions with hitherto un

Conclusions
On the basis of this review is possible to draw some conclusions and determine the further direction of this work: Among the fluoridometallates (IV), the largest number of different anions is known for Ti.This is not so surprising in view of the numerous studies that have been carried out in recent years [5][6][7]11,12,[14][15][16]19,[22][23][24]26,32].The use of some other asymmetrical organic cations could still lead to new anions with hitherto unknown geometry.The examples of Zr and Hf salts are limited to a single case for each element [16].Since both elements prefer a higher coordination than six, it is not very likely that many new examples will be prepared.
[H 3 N(CH 2 ) 2 NH 2 ][VF 5 ] is a unique example of a structurally characterized V(IV) fluoride compound that does not contain only an isolated [VF 6 ] 2− anion [33].Therefore, the chemistry of hybrid compounds with V(IV) is still an unexplored area.In fluorides, vanadium occurs in different oxidation states, ranging from +2 to +5.This could be an obstacle on the way to synthesizing inorganic or hybrid V(IV) fluorides.V(IV)could be reduced, oxidized, or disproportionated, resulting in V(III) and V(V) salts instead of the desired V(IV) salts.There are only a few examples of Nb(IV) fluorides (all are [NbF 6 ] 2− salts [47,48]), while TaF 4 and Ta(IV) fluorides are not known at all.Therefore, these two elements are not good candidates for the preparation of new Nb(IV) and Ta(IV) fluoride polyanions.
The chemistry of Cr(IV) polyanions is limited to salts with inorganic cations such as alkali metals and noble gas fluoride cations [15,28,37].Due to the oxidizing power of Cr(IV), it is not very likely that many new hybrid polyfluoridechromates (IV) could be prepared.It is interesting to note that the [W 4 F 18 ] 2− salt [WCl 2 (cp) 2 ][W 4 F 18 ] (cp = η-C 6 H 5 )] is an example of a W(IV) fluoride salt [20], while [WF 6 ] 2− salts are not known.The Mo(IV) fluoride salts are rare and are limited to [MoF 6 ] 2− salts [49].Therefore, these three elements are also not very promising candidates for the preparation of new M(IV) fluoride polyanions (M = Cr, Mo, W).
For similar reasons as for Cr(IV), Mn(IV) is not a good choice for the preparation of new M(IV) (M = Mn) fluoride polyanions.
The M(IV) fluorides (M = Re, Ru, Os, Rh, Ir, Pd, Pt) are limited to [MF 6 ] 2− salts, and no association of MF 6 octahedra has been observed so far.
In the case of M(IV) (M = Si, Ge, Sn, Pb), there are a number of reports in which selected anions have been observed in solution or suggested by vibrational spectroscopy in the solid state, but the determination of their crystal structures in the solid state is still pending: are unknown [42,50].
Therefore, these elements (especially Sn and Pb) are the most promising for the synthesis of hybrid salts with new fluoridometallate (IV) polyanions.
Although examples of [MF 6 ] 2 salts are known for M = Ce [51], U [51], and Tc [51], it is not very likely that new fluoride polyanions will be synthesized in their case.
We can therefore assume that various oligomeric and polymeric anions still need to be prepared and structurally characterized.

Figure 5 .Figure 6 .
Figure 5. Dimeric [Cr 2 F 11 ] − anion in the crystal structure of K 3 Cr 2 F 11 •2HF with two CrF 6 octahedra sharing a common vertex.2.4.[M 3 F 13 ] − Anion (M = Ti, Ge) Theoretical ab initio calculations have shown that the global minimum structure of the [Ti 3 F 13 ] − anion corresponds to a C 3v -symmetry structure comprising an equilateral triangle of three TiF 6 octahedra that additionally share an F atom over the centre of the triangle (Figure 6) [7].The entire structure can be considered as consisting of three octahedra sharing four F atoms.The oligomeric [Ti 3 F 13 ] − anion, the similar [Ge 3 F 13 ] − isomer, or another [M IV 3 F 13 ] − anion (M = M 4+ ) have not yet been observed experimentally.

2. 6 .
[M 3 F 16 ] 4− Anion (M = Ge) A summary of the crystal data of the salts consisting of [M 3 F 16 ] 4− anions (M = Ge) are given in Table

2. 7 .
[M 4 F 18 ] 2− Anion (M = Ti, W) A summary of the crystal data of the salts consisting of [M 4 F 18 ] 2− anions (M = Ti, W) is given in Table

Table 7 .*
Crystal data of the salt consisting of [M5F23] 3− anions (M = Ti).Crystal structure was determined at the given temperature.

Figure 18 .
Figure 18.Hexameric [Ti 6 F 27 ] 3− anion in the crystal structures of [C(NH 2 ) 3 ] 3 [Ti 6 F 27 ]•SO 2 and [C 3 H 5 N 2 ] 2 [H 3 O][Ti 6 F 27 ].2.12.[M 6 F 28 ] 4− Anion (M = Ti) In the study of the imidazole-TiF 4 -HF system, single crystals of the compound [ImH] 8−n [X] n [Ti 8 F 36 ][Ti 6 F 28 ] were grown [23].Its crystal structure contains two different perfluoridotitanate (IV) anion-cubic [Ti 8 F 36 ] 4− octamers and a hexameric [Ti 6 F 28 ] 4−anion.Unfortunately, it was not possible to accurately determine all cations in the crystal structure, but the proposed models of the anions are well refined.The [Ti 6 F 28 ] 4− anion has a very unusual geometry (Figure19).In the centre are two TiF 6 octahedra that share a vertex.Attached to this pair is a TiF 6 unit that shares a fluorine atom with each of the octahedra.There is also a chain of three TiF 6 octahedra in which each octahedron at the end of the chain shares two vertices with two octahedra in the centre of the [Ti 6 F 28 ] 4− anion.

Figure 46 .
Figure 46.Polymeric chain-like ([Ti 2 F 9 ] − ) ∞ anion in the crystal structure of NaTi 2 F 9 •HF.The single-crystal structure of Rb[Ti 2 F 9 ] consists of an infinite ([Ti 2 F 9 ] − ) ∞ anion in two different conformations (Figure 47) [31].One ([Ti 2 F 9 ] − ) ∞ anion has a gauche conformation of the TiF 6 octahedral pairs belonging to the two single chains of the double chain, as in the anions in the crystal structures of β-H 3 OTi 2 F 9 (Figure 45), while the second anion has an eclipsed conformation of these TiF 6 octahedral pairs, similar to the anion in the crystal structures of α-[H 3 O][Ti 2 F 9 ] (Figure 44).CsTi 2 F 9 crystallizes in the monoclinic space group C2/c (Table14, Figure48)[6], where the Ti-F b -Ti angles within the individual zig-zag chains are kinked with an angle of 156.3(4) • .The Ti-F b -Ti angles where Ti atoms belong to two neighbouring chains are 149.3(6)• [6].
The infinite two-dimensional (2-D) arrangement of poly[per anions is observed in the case of the ([Ti8F33] − )∞ anion characteriz [Xe2F3][Ti8F33] [45].In both cases, the ([Ti8F33] − )∞ anion represents a different structural motifs.In CsTi8F33, two Ti atoms are coordinated by three bridgi fluorine atoms, while the other two are coordinated by four brid fluorine atoms, ultimately leading to a 2-D framework (Figure 58)

Figure 60 .
Figure 60.Packing of polymeric anionic layers ([Cr 2 F 9 ] − ) ∞ in the crystal structure of XeF 2 •2CrF 4 .7.Polymeric ([M 6 F 27 ] 3− ) ∞ Anion in the Form of Three-Dimensional Framework (M = Ti)A summary of the crystal data of the salt consisting of polymeric ([M 6 F 27 ] 3− ) ∞ anion (M = Ti) in the form of a three-dimensional framework is given in Table17.
Slow decomposition in attempts to grow single crystals of K 4 [Ti 8 F 36 ]•8HF and Rb 4 [Ti 8 F 36 ]•6HF [24] led to the growth of cube-shaped crystals of ([Ti 6 F 27 ] 3− ) ∞ salts.Later, the same type of anion ([Ti 6 F 27 ] 3− ) ∞ was found in [H 3 O] 3 [Ti 6 F 27 ] [31].Unfortunately, in all three cases, there is a problem with charge balance, i.e., a deficit of cations.For K and Rb salts, there is a possibility that some [H 3 O] + was present, leading to mixed-cation A + /[H 3 O] + salts.
* The crystal structures were determined at the indicated temperatures.
* The crystal structures were determined at the indicated temperatures.
* The crystal structure was determined at the indicated temperature.
* The crystal structures were determined at the indicated temperatures.
* The crystal structures were determined at the indicated temperatures.**Measured at room temperature.The exact temperature was not reported.
* The crystal structure was determined at the indicated temperature.
* The crystal structures were determined at the indicated temperatures.*The crystal structures were determined at the indicated temperatures.

Table 16 .
Crystal data of the salts consisting of layered ([M 8 F 33 ] − ) ∞ and ([M 2 F 9 ] − ) ∞ anions (M = Ti, Cr).Crystal structures were determined at the indicated temperatures.** Measured at room temperature.The exact temperature was not reported. *

Table 17 .
Crystal data of the salt consisting of polymeric ([M 6 F 27 ] 3− ) ∞ anion (M = Ti) in the form of a three-dimensional framework.
* The crystal structure was determined at the indicated temperature.
The crystal structure was determined at the indicated temperature. *