Structural and theoretical studies of Xe(OChF5)2 and [XeOChF5][AsF6] (Ch = Se, Te)

The XeOSeF₅⁺ cation has been synthesized for the first time and characterized in solution by ¹⁹F, ⁷⁷Se and ¹²⁹Xe NMR spectroscopy and in the solid state by X-ray crystallography and Raman spectroscopy with AsF₆⁻ as its counter anion. The X-ray crystal structures of the tellurium analogue and of the Xe(OChF₅)₂ derivatives have also been determined: [XeOChF₅][AsF₆] crystallize in tetragonal systems, P4/n, a=6.1356(1) Å, c=13.8232(2) Å, V=520.383(14) Å³, Z=2 and R₁=0.0453 at −60°C (Te) and a=6.1195(7) Å, c=13.0315(2) Å, V=488.01(8) Å³, Z=2 and R₁=0.0730 at −113°C (Se); Xe(OTeF₅)₂ crystallizes in a monoclinic system, P2₁/c, a=10.289(2) Å, b=9.605(2) Å, c=10.478(2) Å, β=106.599(4)°, V=992.3(3) Å³, Z=4 and R₁=0.0680 at −127°C; Xe(OSeF₅)₂ crystallizes in a triclinic system, , a=8.3859(6) Å, c=12.0355(13) Å, V=732.98(11) Å³, Z=3 and R₁=0.0504 at −45°C. The energy minimized geometries and vibrational frequencies of the XeOChF₅⁺ cations and Xe(OChF₅)₂ were calculated using density functional theory, allowing for definitive assignments of their experimental vibrational spectra.     

Synthesis, structure and magnetic properties of A2MnB′O6 (A=Ca, Sr; B′=Sb, Ta) double perovskites

A₂MnB′O₆ (A=Ca, Sr; B=Sb, Ta) double perovskites have been synthesized and their structural and magnetic properties have been investigated. Rietveld refinement of the powder X-ray diffraction data for Sr₂MnSbO₆ indicated significant ordering of Mn and Sb at the B-site while all other phases showed mostly a random distribution of the B-site cations. X-ray absorption spectroscopic data established the presence of Mn in the 3+ and Sb/Ta in the 5+ oxidation states in all the phases. Magnetic susceptibility data indicated ferromagnetic correlations for all the A₂MnB′O₆ phases with Weiss temperatures varying from 64 to 107 K.     

New octahedral Ta(V) hydrazido-substituted compounds for atomic layer deposition: Syntheses,X-ray diffraction structures of TaCl(NMe2)3[N(TMS)NMe2] and Ta(NMe2)4[N(TMS)NMe2], and fluxional behavior of the amido and hydrazido ligands in solution

The synthesis and structural characterization of new tantalum(V) compounds containing a single hydrazido(I) ligand are reported. Hydrazinolysis of TaCl(NMe₂)₄ using trimethylsilyl(dimethyl)hydrazine affords the compound TaCl(NMe₂)₃[N(TMS)NMe₂] in essentially quantitative yield. Metathetical replacement of the chloride ligand in TaCl(NMe₂)₃[N(TMS)NMe₂] by LiNMe₂ gives the all-nitrogen coordinated compound Ta(NMe₂)₄[N(TMS)NMe₂]. VT ¹H NMR studies support the existence of low-energy pathways involving rotation about the Ta–N bonds of the ancillary amido and hydrazido ligands in both hydrazido-substituted compounds. X-ray crystallographic analyses confirm the octahedral disposition about the tantalum metal in TaCl(NMe₂)₃[N(TMS)NMe₂] and Ta(NMe₂)₄[N(TMS)NMe₂] and the presence of an η²-hydrazido(I) ligand. Preliminary data using Ta(NMe₂)₄[N(TMS)NMe₂] as an ALD precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.     

Structure of the Ligated Ag60 Nanoparticle [{Cl@Ag12}@Ag48(dppm)12] (where dppm=bis(diphenylphosphino)methane)

A novel bisphosphine ligated Ag₆₀ nanocluster, [{Cl@Ag₁₂}@Ag₄₈(dppm)₁₂], has been dis-covered and characterized by X-ray crystallography. It consists of a central chloride located inside an icosahedral silver core layer, which is further encased by a second shell of 48 silver atoms/ions, which are capped with 12 bis(diphenylphosphino)methane (dppm) ligands. Due to lack of sufficient material the cluster could not be further characterized by other methods. DFT calculations were carried out on the cation [{Cl@Ag₁₂}@Ag₄₈(dppm)₁₂]⁺ to determine if it corresponds to a superatom with a core count of n=58. The DFT optimized structure is in agreement with X-ray ndings, but the low value of the HOMO-LUMO gap does not support superatom stability.     

Formation and structural characterization of mercury complexes from Te(R)CH2SiMe3 (R = Ph, CH2SiMe3) and HgCl2

The reaction of HgCl₂ and Te(R)CH₂SiMe₃ [R = CH₂SiMe₃ (1), Ph (2)] in ethanol yielded a mononuclear complex [HgCl₂{Te(R)CH₂SiMe₃}₂] (R = Ph, 3a; R = CH₂SiMe₃, 3b). The recrystallization of 3a or 3b from CH₂Cl₂ produced a dinuclear complex [Hg₂Cl₂(μ-Cl)₂{Te(R)CH₂SiMe₃}₂] (R = Ph, 4a; R = CH₂SiMe₃, 4b). When 3a was dissolved in CH₂Cl₂, the solvent quickly removed, and the solid recrystallized from EtOH, a stable ionic [HgCl{Te(Ph)CH₂SiMe₃}₃]Cl·2EtOH (5a·2EtOH) was obtained. Crystals of [HgCl₂{Te(CH₂SiMe)₂}]·2HgCl₂·CH₂Cl₂ (6b·2HgCl₂·CH₂Cl₂) were obtained from the CH₂Cl₂ solution of 3b upon prolonged standing. The complex formation was monitored by ¹²⁵Te-, and ¹⁹⁹Hg NMR spectroscopy, and the crystal structures of the complexes were determined by single crystal X-ray crystallography.     

Phase composition and phase transformation in Bi(Sb,Nb,Ta)O4 system

In this work Bi(Sb_xNb_yTa_z)O₄ (x + y + z = 1) samples are prepared using mixed-oxide method. A pseudo-ternary phase diagram of Bi(Sb,Nb,Ta)O₄ system is given below the melting point. It is composed of a monoclinic phase region, an orthorhombic phase region and a monoclinic–orthorhombic co-existing phase region. In the orthorhombic phase region, the transformation from orthorhombic to triclinic phase is found to be sensitive to the composition and sintering temperature. Both the transformation from monoclinic to orthorhombic structure and the transformation from orthorhombic to triclinic structure have been studied by the cell parameters.     

Crystal structure, spectroscopy and thermodynamic properties of MVWO6(M – Li, Na)

In the present work lithium (sodium) vanadium tungsten oxides with brannerite structure is refined by the Rietveld method (space group C2/m, Z=2). IR and Raman spectroscopy was used to assign vibrational bands and determine structural particularities. The diffuse reflectance spectra allow to calculate bandgap for M^IVWO₆(M^I – Li, Na). The temperature dependences of heat capacity have been measured first in the range from 7 to 350 K for these compounds and then between 330 and 640 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p^o(T), enthalpy H^o(T)−H^o(0), entropy S^o(T)−S^o(0) and Gibbs function G^o(T)−H^o(0), for the range from T→0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study.     

Syntheses, structures, and vibrational spectroscopy of the two-dimensional iodates Ln(IO3)3 and Ln(IO3)3(H2O) (LnYb, Lu)

The reaction of Lu³⁺ or Yb³⁺ and H₅IO₆ in aqueous media at 180 °C leads to the formation of Yb(IO₃)₃(H₂O) or Lu(IO₃)₃(H₂O), respectively, while the reaction of Yb metal with H₅IO₆ under similar reaction conditions gives rise to the anhydrous iodate, Yb(IO₃)₃. Under supercritical conditions Lu³⁺ reacts with HIO₃ and KIO₄ to yield the isostructural Lu(IO₃)₃. The structures have been determined by single-crystal X-ray diffraction. Crystallographic data are (MoKα, λ=0.71073 Å): Yb(IO₃)₃, monoclinic, space group P2₁/n, a=8.6664(9) Å, b=5.9904(6) Å, c=14.8826(15) Å, β=96.931(2)°, V=766.99(13), Z=4, R(F)=4.23% for 114 parameters with 1880 reflections with I>2σ(I); Lu(IO₃)₃, monoclinic, space group P2₁/n, a=8.6410(9), b=5.9961(6), c=14.8782(16) Å, β=97.028(2)°, V=765.08(14), Z=4, R(F)=2.65% for 119 parameters with 1756 reflections with I>2σ(I); Yb(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.2476(15), b=5.6296(3), c=12.0157(7) Å, β=98.636(1)°, V=1822.2(2), Z=8, R(F)=1.51% for 128 parameters with 2250 reflections with I>2σ(I); Lu(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.258(4), b=5.6251(7), c=12.0006(16) Å, β=98.704(2)°, V=1818.8(4), Z=8, R(F)=1.98% for 128 parameters with 2242 reflections with I>2σ(I). The f elements in all of the compounds are found in seven-coordinate environments and bridged with monodentate, bidentate, or tridentate iodate anions. Both Lu(IO₃)₃(H₂O) and Yb(IO₃)₃(H₂O) display distinctively different vibrational profiles from their respective anhydrous analogs. Hence, the Raman profile can be used as a complementary diagnostic tool to discern the different structural motifs of the compounds.     

Synthesis, crystal structure and spectroscopy properties of Na3AZr(PO4)3 (A=Mg, Ni) and Li2.6Na0.4NiZr(PO4)3 phosphates

Na₃AZr(PO₄)₃ (A=Mg, Ni) phosphates were prepared at 750 °C by coprecipitation route. Their crystal structures have been refined at room temperature from X-ray powder diffraction data using Rietveld method. Li_2.6Na_0.4NiZr(PO₄)₃ was synthesized through ion exchange from the sodium analog. These materials belong to the Nasicon-type structure. Raman spectra of Na₃AZr(PO₄)₃ (A=Mg, Ni) phosphates present broad peaks in favor of the statistical distribution in the sites around PO₄ tetrahedra. Diffuse reflectance spectra indicate the presence of octahedrally coordinated Ni²⁺ ions.     

Synthesis, characterization, protonation studies and X-ray crystal structure of ReH5(PPh3)2(PTA) (PTA = 1,3,5-triaza-7-phosphaadamantane)

The novel rhenium pentahydride complex [ReH₅(PPh₃)₂(PTA)] (2) was synthesized by dihydrogen replacement from the reaction of [ReH₇(PPh₃)₂] with PTA in refluxing THF. Variable temperature NMR studies indicate that 2 is a classic polyhydride (T_1(min) = 133 ms). This result agrees with the structure of 2, determined by X-ray crystallography at low temperature. The compound shows high conformational rigidity which allows for the investigation of the various hydride-exchanging processes by NMR methods. Reactions of 2 with equimolecular amounts of either HFIP or HBF₄ · Et₂O at 183 K afford [ReH₅(PPh₃)₂{PTA(H)}]⁺ (3) via protonation of one of the nitrogen atoms on the PTA ligand. When 5 equivalents of HBF₄ · Et₂O are used, additional protonation of one hydride ligand takes place to generate the thermally unstable dication [ReH₄(η²-H₂)(PPh₃)₂{PTA(H)}]²⁺ (4), as confirmed by ¹H NMR and T₁ analysis. IR monitoring of the reaction between 2 and CF₃COOD at low temperature shows the formation of the hydrogen bonded complex [ReH₅(PPh₃)₂{PTA?DOC(O)CF₃}] (5) and of the ionic pair [ReH₅(PPh₃)₂{PTA(D)?OC(O)CF₃}] (6) preceding the proton transfer step leading to 3.     

Steric and electronic effects in stabilizing allyl-palladium complexes of “P-N-P” ligands, X2PN(Me)PX2 (X = OC6H5 or OC6H3Me2-2,6)

The chemistry of η³-allyl palladium complexes of the diphosphazane ligands, X₂PN(Me)PX₂ [X = OC₆H₅ (1) or OC₆H₃Me₂-2,6 (2)] has been investigated.The reactions of the phenoxy derivative, (PhO)₂PN(Me)P(OPh)₂ with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = H or Me; R′ = H, R″ = Me) give exclusively the palladium dimer, [Pd₂{μ-(PhO)₂PN(Me)P(OPh)₂}₂Cl₂] (3); however, the analogous reaction with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = Ph) gives the palladium dimer and the allyl palladium complex [Pd(η³-1,3-R′,R″-C₃H₃)(1)](PF₆) (R′ = R″ = Ph) (4). On the other hand, the 2,6-dimethylphenoxy substituted derivative 2 reacts with (allyl) palladium chloro dimers to give stable allyl palladium complexes, [Pd(η³-1,3-R′,R″-C₃H₃)(2)](PF₆) [R′ = R″ = H (5), Me (7) or Ph (8); R′ = H, R″ = Me (6)].Detailed NMR studies reveal that the complexes 6 and 7 exist as a mixture of isomers in solution; the relatively less favourable isomer, anti-[Pd(η³-1-Me-C₃H₄)(2)](PF₆) (6b) and syn/anti-[Pd(η³-1,3-Me₂-C₃H₃)(2)](PF₆) (7b) are present to the extent of 25% and 40%, respectively. This result can be explained on the basis of the steric congestion around the donor phosphorus atoms in 2. The structures of four complexes (4, 5, 7a and 8) have been determined by X-ray crystallography; only one isomer is observed in the solid state in each case.     

Preparation, XRD and Raman spectroscopic studies on new compounds RE2Hf2O7 (RE=Dy, Ho, Er, Tm, Lu, Y): Pyrochlores or defect-fluorite?

A series of compositions with the general formula RE₂Hf₂O₇ (RE=Dy, Ho, Er, Tm, Y and Lu) was prepared by a standard solid-state route and characterized by powder X-ray diffraction (XRD) and Raman spectroscopy. As per theoretical modeling reported in literature, some of these materials were predicted to exist in pyrochlore lattice. However, a careful X-ray diffraction, Raman spectroscopic and synchrotron radiation-XRD study revealed that under the experimental conditions used in the present investigation, out of all the RE₂Hf₂O₇ samples only Dy₂Hf₂O₇ has got a tendency to form a pyrochlore structure. All the other (Ho, Er, Tm, Lu, Y) hafnates crystallize in a defect-fluorite structure. In order to further ascertain these inferences, a few more RE₂Hf₂O₇ samples (La, Nd, Sm) i.e., with larger RE³⁺ ions were also prepared and the results were compared.     

4,5-Bis[(triorganotin)thiolato]-1,3-dithiole-2-thione, (R3Sn)2(dmit), 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-one, (R3Sn)2(dmio), compounds: Crystal structures of (cyclohexyl3Sn)2(dmio), (Ph3Sn)2(dmit) and (Ph3Sn)2(dmio)

The synthesis and crystal structures of 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-thione, (R₃Sn)₂(dmit), 1, and 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-one, (R₃Sn)₂(dmio), 2, compounds are reported. Compounds, (1 or 2: R = Ph or cyclohexyl, Cy), have been obtained from reaction of R₃SnCl with Cs₂dmit or Na₂dmio. The presence of the two tin centres in (2: R = Ph) is shown in the ¹³C NMR spectrum by the couplings of both Sn atoms to the dmio olefinic carbons with J values of 29.4 and 24.7 Hz. The δ¹¹⁹ Sn values for (1: R = Ph) and (2: R = Ph) differ by about 30 ppm, values being −20.7 and −50.1 ppm, respectively, in CDCl₃ solution. X-ray structure determinations for (1: R = Ph) and (2: R = Ph or Cy) reveal the compounds to have 4-coordinate, distorted tetrahedral tin centres. The dithiolato ligands, dmit and dmio, act as bridging ligands, in contrast to their chelating roles in R₂Sn(dmit) and R₂Sn(dmio). A further difference between R₂Sn(dmit) and R₂Sn(dmio), on one hand, and 1 and 2 on the other, is that intermolecular Sn-S and Sn-O interactions are absent in 1 and 2. However, weak intermolecular hydrogen bonding interactions are found in (1: R = Ph) [C-H?π] and in (2: R = Ph) [C-H?π and C-H?O].     

Synthesis and structure of In(IO3)3 and vibrational spectroscopy of M(IO3)3 (M=Al, Ga, In)

The reaction of Al, Ga, or In metals and H₅IO₆ in aqueous media at 180 °C leads to the formation of Al(IO₃)₃, Ga(IO₃)_3, or In(IO₃)₃, respectively. Single-crystal X-ray diffraction experiments have shown In(IO₃)₃ contains the Te₄O₉-type structure, while both Al(IO₃)₃ and Ga(IO₃)₃ are known to exhibit the polar Fe(IO₃)₃-type structure. Crystallographic data for In(IO₃)₃, trigonal, space group , a=9.7482(4) Å, c=14.1374(6) Å, V=1163.45(8) Z=6, R(F)=1.38% for 41 parameters with 644 reflections with I>2σ(I). All three iodate structures contain group 13 metal cations in a distorted octahedral coordination environment. M(IO₃)₃ (M=Al, Ga) contain a three-dimensional network formed by the bridging of Al³⁺ or Ga³⁺ cations by iodate anions. With In(IO₃)₃, iodate anions bridge In³⁺ cations in two-dimensional layers. Both materials contain distorted octahedral holes in their structures formed by terminal oxygen atoms from the iodate anions. The Raman spectra have been collected for these metal iodates; In(IO₃)₃ was found to display a distinctively different vibrational profile than Al(IO₃)₃ or Ga(IO₃)₃. Hence, the Raman profile can be used as a rapid diagnostic tool to discern between the different structural motifs.     

Magnetism and Raman spectroscopy of the dimeric lanthanide iodates Ln(IO3)3 (Ln=Gd, Er) and magnetism of Yb(IO3)3

Colorless single crystals of Gd(IO₃)₃ or pale pink single crystals of Er(IO₃)₃ have been formed from the reaction of Gd metal with H₅IO₆ or Er metal with H₅IO₆ under hydrothermal reaction conditions at 180 °C. The structures of both materials adopt the Bi(IO₃)₃ structure type. Crystallographic data are (MoKα, λ=0.71073 Å): Gd(IO₃)₃, monoclinic, space group P2₁/n, a=8.7615(3) Å, b=5.9081(2) Å, c=15.1232(6) Å, β=96.980(1)°, V=777.03(5) Z=4, R(F)=1.68% for 119 parameters with 1930 reflections with I>2σ(I); Er(IO₃)₃, monoclinic, space group P2₁/n, a=8.6885(7) Å, b=5.9538(5) Å, c=14.9664(12) Å, β=97.054(1)°, V=768.4(1) Z=4, R(F)=2.26% for 119 parameters with 1894 reflections with I>2σ(I). In addition to structural studies, Gd(IO₃)₃, Er(IO₃)₃, and the isostructural Yb(IO₃)₃ were also characterized by Raman spectroscopy and magnetic property measurements. The results of the Raman studies indicated that the vibrational profiles are adequately sensitive to distinguish between the structures of the iodates reported here and other lanthanide iodate systems. The magnetic measurements indicate that only in Gd(IO₃)₃ did the 3+ lanthanide ion exhibit its full 7.9 μ_B Hund's rule moment; Er³⁺ and Yb³⁺ exhibited ground state moments and gap energy scales of 8.3 μ_B/70 K and 3.8 μ_B/160 K, respectively. Er(IO₃)₃ exhibited extremely weak ferromagnetic correlations (+0.4 K), while the magnetic ions in Gd(IO₃)₃ and Yb(IO₃)₃ were fully non-interacting within the resolution of our measurements (∼0.2 K).     

Syntheses and structures of six compounds in the A2LiMS4 (A=K, Rb, Cs; M=V, Nb, Ta) family

Six new compounds in the A₂LiMS₄ (A=K, Rb, Cs; M=V, Nb, Ta) family, namely K₂LiVS₄, Rb₂LiVS₄, Cs₂LiVS₄, Rb₂LiNbS₄, Cs₂LiNbS₄, and Rb₂LiTaS₄, have been synthesized by the reactions of the elements in Li₂S/S/A₂S₃ (A=K, Rb, Cs) fluxes at 773 K. The A and M atoms play a role in the coordination environment of the Li atoms, leading to different crystal structures. Coordination numbers of Li atoms are five in K₂LiVS₄, four in A₂LiVS₄ (A=Rb, Cs) and Cs₂LiNbS₄, and both four and five in Rb₂LiMS₄ (M=Nb, Ta). The A₂LiVS₄ (A=Rb, Cs) structure comprises one-dimensional chains of tetrahedra. The Rb₂LiMS₄ (M=Nb, Ta) structure is composed of two-dimensional layers. The Cs₂LiNbS₄ structure contains one-dimensional chains that are related to the Rb₂LiMS₄ layers. The K₂LiVS₄ structure contains a different kind of layer.     

Excellent red phosphors of double perovskite Ca2LaMO6:Eu (M=Sb, Nb, Ta) with distorted coordination environment

Double perovskite Ca₂LaSbO₆, successfully synthesized by solid state reaction method, was identified by Rietveld refinements to crystallize in the monoclinic space group P2₁/n, which is isostructural to Ca₂LaMO₆ (M=Nb, Ta). Excellent red luminescence of Eu-doped Ca₂LaMO₆ (M=Sb, Nb, Ta) can be obtained and no luminescence quenching effect was observed when Eu-doping level reached 40%. For Ca₂La_0.6NbO₆:0.4Eu³⁺, quantum efficiencies of 20.9% and 27.7% were reached to show high light conversion and bright red emission excited at 465 nm (blue light) and 534 nm (green light), respectively, comparable to the commercial phosphors. Through systemic investigation for the series of double perovskite compounds, the excellent red emission in Ca₂LaMO₆ is attributed to highly distorted polyhedra of EuO₈ (low tolerance factor of the pervoskite), and large bond distances of La−O (low crystal field effect of the activator).     

Dielectric properties of some MM′O4 and MTiM′O6 (M=Cr, Fe, Ga; M′=Nb, Ta, Sb) rutile-type oxides

We describe an investigation of the structure and dielectric properties of MM′O₄ and MTiM′O₆ rutile-type oxides for M=Cr, Fe, Ga and M′=Nb, Ta and Sb. All the oxides adopt a disordered rutile structure (P4₂/mnm) at ambient temperature. A partial ordered trirutile-type structure is confirmed for FeTaO₄ from the low temperature (17 K) neutron diffraction studies. While both the MM′O₄ oxides (CrTaO₄ and FeTaO₄) investigated show a normal dielectric property MTiM′O₆ oxides for M=Fe, Cr and M′=Nb/Ta/Sb display a distinct relaxor/relaxor-like response. Significantly the corresponding gallium analogs, GaTiNbO₆ and GaTiTaO₆, do not show a relaxor response at T<500 K.     

Synthesis, vibrational and NMR spectroscopic characterization of [N(CH3)4][IO2F2] and X-ray crystal structure of [N(CH3)4]2[IO2F2][HF2]

The salt, [N(CH₃)₄][IO₂F₂], was prepared from [N(CH₃)₄][IO₃] and 49% aqueous HF, and characterized by Raman, infrared, and ¹⁹F NMR spectroscopy. Crystals of [N(CH₃)₄]₂[IO₂F₂][HF₂] were obtained by reduction of [N(CH₃)₄][cis-IO₂F₄] in the presence of [N(CH₃)₄][F] in CH₃CN solvent and were characterized by Raman spectroscopy and single-crystal X-ray diffraction: C2/m, a = 14.6765(2) Å, b = 8.60490(10) Å, c = 13.9572(2) Å, β = 120.2040(10)°, V = 1523.35(3) Å³, Z = 4 and R = 0.0192 at 210 K. The crystal structure consists of two IO₂⁻F₂ anions that are symmetrically bridged by two H⁻F₂ anions, forming a [F₂O₂I(FHF)₂IO₂F₂]⁴⁻ dimer. The symmetric bridging coordination for the H⁻F₂ anion in this structure represents a new bonding modality for the bifluoride anion.