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The title compound, AgTcO4, contains close Ag-O contacts, and Raman spectroscopy shows a reduction in the Tc-O stretching frequencies on changing the pertechnetate counter-cation from K+ to Ag+.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103006486/sk1620sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103006486/sk1620Isup2.hkl
Contains datablock I

Comment top

Within the nuclear industry, technetium is an important fission product that exists predominantly in the highest oxidation state (VII) as the pertechnetate anion [TcO4]. An understanding of the chemistry of pertechnetate in forming complexes, either through covalent bonding or as a counter-anion, is important in the context of nuclear fuel reprocessing and waste management (Wilson, 1996). It has been previously shown that the perrhenate analogue [ReO4] readily forms complexes through oxygen coordination to a range of d- and f-transition metal centres (Chakravorti, 1990). However, there are no related investigations into the coordinating ability of [TcO4], possibly because all Tc isotopes are radioactive. Here we describe evidence that, in the solid state, considerable covalent- bonding interactions occur between pertechnetate anions and silver cations.

The compound AgTcO4 crystallizes in a high-symmetry space group (I41/a), with three atoms in the asymmetric unit, and is isostructural with AgReO4 (Naumov et al., 1999). A packing diagram and a polyhedral representation of the bonding around the Tc and Ag atoms are illustrated in Fig. 1. I Interatomic distances and angles are shown in Table 1. The 16t h, 17t h and 18t h lowest O—Ag—O bond angles are equivalent, predicting a triangular dodecahedral geometry around the Ag atom (Fig. 1 b) according to the coordination geometry rules for eight-coordinate complexes (Haigh, 1995). The Tc atom resides in a slightly distorted tetrahedon in AgTcO4, with O—Tc—O angles of 108.52 (16) and 111.4 (3)°, compared with 110.0 (1) and 109.2 (1)° in [NH4][TcO4] and 110.5 (2) and 109.0 (2)° in KTcO4. Each O atom bridges one Tc and two Ag atoms. The Tc—O bond length [1.724 (5) Å] is similar to that in KTcO4 [1.711 (3) Å; Krebs & Hasse, 1976], [NH4][TcO4] [1.711 (1) Å; Faggiani et al., 1980] and AgReO4 [Re—O 1.732 (4); Naumov et al., 1999]. The average Ag—O bond lengths in AgTcO4 [2.532 (5) and 2.596 (5), mean 2.564 Å] are shorter than in the isostructural AgClO4 [2.728 (6) and 2.527 (6), mean 2.627 Å; Berthold et al., 1976], and are considerably shorter than those in KTcO4 [2.794 (3) and 2.864 (3), mean 2.829 Å; Krebs & Hasse, 1976], even after correcting for the difference in ionic radii (mean 2.699 Å; rK+ - rAg+ = 0.13 Å for eight-coordinated M+ ions; Winter, 2002).

The short Ag—O contact in AgTcO4 suggests an unusually strong interaction between the pertechnetate and silver ions, which can be detected by the influence on the Tc—O bond strengths. When considering the relative bond strengths in related compounds, the difference in stretching frequency (Δν) in Raman spectroscopy is more sensitive as a probe than X-ray diffraction techniques. In order to interpret the Raman spectrum of AgTcO4 we have collated Raman data for the related compounds KTcO4, [NH4][TcO4], AgReO4 and KReO4 (Table 2); all contain the [MO4] ion in the same S4 site symmetry, allowing a comparative study (Wilson et al., 1995; Decius & Hexter, 1977). The correlation tables for such site symmetry predict three Raman active stretching vibration frequencies with one symmetric [A species, ν1(a1)], identified by polarization experiments, and two asymmetric vibrations assigned to B and E [both from ν3(f2)], with E being of higher intensity than B (Wilson et al., 1995). Raman data for KTcO4 (Busey & Keller, 1964), a compound with long K—O bond lengths (see above) and weak cation–oxygen interactions, has slightly higher symmetric and asymmetric vibrations (Table 2) than those observed for [NH4][TcO4] [Δν1 = 5, Δν3(B) = 12 and Δν3(E) = 7 cm−1; Faggiani et al., 1980] because of the hydrogen-bonding network within the structure of the latter. By comparison, stretching vibrations for AgTcO4 are shifted to a much lower energy relative to KTcO4ν1 = 33, Δν3(B) = 24 and Δν3(E) = 40 cm−1], and such large shifts in the Raman lines infer considerable covalent bonding between silver and pertechnetate ions in the solid state. This situation is consistent with that for related silver salts? when compared with their respective potassium salts; indeed, there are large shifts to lower frequency in the Raman lines for perrhenate ions [Δν1 = 24, Δν3(B) = 25 and Δν3(E) = 35 cm−1; Busey & Keller, 1964].

Both single-crystal X-ray diffraction and Raman spectroscopy indicate that there are significant interactions between Ag+ and [TcO4] ions, suggesting that [TcO4] may be on a par with or better than perrhenate as a coordinating ligand to other metal centres.

Experimental top

The title compound was synthesized as described by Nugent (1983). Recrystallization from water afforded pale-yellow crystals suitable for X-ray analysis.

Refinement top

The metal atoms were refined anisotropically and O1 was refined isotropically.

Computing details top

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: DIAMOND (Brandenburg, 2001).

Figures top
[Figure 1] Fig. 1. (a) Extended lattice of AgTcO4 viewed along the crystallographic b axis. (b) Polyhedron representation of the geometry around the Ag and Tc atoms.
(I) top
Crystal data top
AgTcO4Dx = 5.398 Mg m3
Mr = 269.87Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I41/aCell parameters from 779 reflections
Hall symbol: -I 4adθ = 6.5–28.1°
a = 5.3026 (12) ŵ = 9.89 mm1
c = 11.810 (5) ÅT = 100 K
V = 332.07 (18) Å3Block, yellow
Z = 40.20 × 0.10 × 0.10 mm
F(000) = 488
Data collection top
CCD area detector
diffractometer
204 independent reflections
Radiation source: fine-focus sealed tube200 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.016
ϕ and ω scansθmax = 28.1°, θmin = 3.5°
Absorption correction: multi-scan
SADABS, Bruker SHELXTL
h = 76
Tmin = 0.242, Tmax = 0.438k = 66
1395 measured reflectionsl = 1515
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.039Secondary atom site location: difference Fourier map
wR(F2) = 0.093 w = 1/[σ2(Fo2) + (0.0288P)2 + 9.6708P]
where P = (Fo2 + 2Fc2)/3
S = 1.45(Δ/σ)max < 0.001
204 reflectionsΔρmax = 0.69 e Å3
10 parametersΔρmin = 1.19 e Å3
Crystal data top
AgTcO4Z = 4
Mr = 269.87Mo Kα radiation
Tetragonal, I41/aµ = 9.89 mm1
a = 5.3026 (12) ÅT = 100 K
c = 11.810 (5) Å0.20 × 0.10 × 0.10 mm
V = 332.07 (18) Å3
Data collection top
CCD area detector
diffractometer
204 independent reflections
Absorption correction: multi-scan
SADABS, Bruker SHELXTL
200 reflections with I > 2σ(I)
Tmin = 0.242, Tmax = 0.438Rint = 0.016
1395 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.03910 parameters
wR(F2) = 0.0930 restraints
S = 1.45Δρmax = 0.69 e Å3
204 reflectionsΔρmin = 1.19 e Å3
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ag10.00000.25000.12500.0057 (4)
Tc10.50000.75000.12500.0040 (4)
O10.2663 (9)0.6176 (9)0.0427 (4)0.0034 (8)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ag10.0053 (4)0.0053 (4)0.0063 (6)0.0000.0000.000
Tc10.0034 (5)0.0034 (5)0.0052 (6)0.0000.0000.000
Geometric parameters (Å, º) top
Ag1—O1i2.532 (5)Ag1—O1vii2.596 (5)
Ag1—O1ii2.532 (5)Tc1—O11.724 (5)
Ag1—O1iii2.532 (5)Tc1—O1viii1.724 (5)
Ag1—O1iv2.532 (5)Tc1—O1ix1.724 (5)
Ag1—O1v2.596 (5)Tc1—O1x1.724 (5)
Ag1—O1vi2.596 (5)O1—Ag1iii2.532 (5)
Ag1—O12.596 (5)
O1i—Ag1—O1ii77.1 (2)O1v—Ag1—O1136.0 (2)
O1i—Ag1—O1iii127.73 (13)O1vi—Ag1—O198.06 (8)
O1ii—Ag1—O1iii127.73 (13)O1i—Ag1—O1vii67.17 (11)
O1i—Ag1—O1iv127.73 (13)O1ii—Ag1—O1vii78.59 (16)
O1ii—Ag1—O1iv127.73 (13)O1iii—Ag1—O1vii73.93 (9)
O1iii—Ag1—O1iv77.1 (2)O1iv—Ag1—O1vii149.61 (19)
O1i—Ag1—O1v149.61 (19)O1v—Ag1—O1vii98.06 (8)
O1ii—Ag1—O1v73.93 (9)O1vi—Ag1—O1vii136.0 (2)
O1iii—Ag1—O1v67.17 (11)O1—Ag1—O1vii98.06 (8)
O1iv—Ag1—O1v78.59 (16)O1—Tc1—O1viii108.52 (16)
O1i—Ag1—O1vi78.59 (16)O1—Tc1—O1ix108.52 (16)
O1ii—Ag1—O1vi67.17 (11)O1viii—Tc1—O1ix111.4 (3)
O1iii—Ag1—O1vi149.61 (19)O1—Tc1—O1x111.4 (3)
O1iv—Ag1—O1vi73.93 (9)O1viii—Tc1—O1x108.52 (16)
O1v—Ag1—O1vi98.06 (8)O1ix—Tc1—O1x108.52 (16)
O1i—Ag1—O173.93 (9)Tc1—O1—Ag1iii136.8 (3)
O1ii—Ag1—O1149.61 (19)Tc1—O1—Ag1119.1 (2)
O1iii—Ag1—O178.59 (17)Ag1iii—O1—Ag1101.41 (16)
O1iv—Ag1—O167.17 (11)
O1viii—Tc1—O1—Ag1iii70.47 (18)O1v—Ag1—O1—Tc1156.9 (3)
O1ix—Tc1—O1—Ag1iii168.3 (4)O1vi—Ag1—O1—Tc146.4 (3)
O1x—Tc1—O1—Ag1iii48.9 (3)O1vii—Ag1—O1—Tc192.6 (3)
O1viii—Tc1—O1—Ag186.7 (4)O1i—Ag1—O1—Ag1iii135.06 (17)
O1ix—Tc1—O1—Ag134.5 (3)O1ii—Ag1—O1—Ag1iii152.9 (2)
O1x—Tc1—O1—Ag1153.9 (3)O1iii—Ag1—O1—Ag1iii0.0
O1i—Ag1—O1—Tc129.2 (3)O1iv—Ag1—O1—Ag1iii80.6 (2)
O1ii—Ag1—O1—Tc111.4 (5)O1v—Ag1—O1—Ag1iii38.81 (10)
O1iii—Ag1—O1—Tc1164.3 (4)O1vi—Ag1—O1—Ag1iii149.34 (18)
O1iv—Ag1—O1—Tc1115.09 (18)O1vii—Ag1—O1—Ag1iii71.71 (6)
Symmetry codes: (i) y+3/4, x+1/4, z+1/4; (ii) y3/4, x+1/4, z+1/4; (iii) x, y+1, z; (iv) x, y1/2, z; (v) x, y+1/2, z; (vi) y1/4, x+1/4, z+1/4; (vii) y+1/4, x+1/4, z+1/4; (viii) y1/4, x+5/4, z+1/4; (ix) y+5/4, x+1/4, z+1/4; (x) x+1, y+3/2, z.

Experimental details

Crystal data
Chemical formulaAgTcO4
Mr269.87
Crystal system, space groupTetragonal, I41/a
Temperature (K)100
a, c (Å)5.3026 (12), 11.810 (5)
V3)332.07 (18)
Z4
Radiation typeMo Kα
µ (mm1)9.89
Crystal size (mm)0.20 × 0.10 × 0.10
Data collection
DiffractometerCCD area detector
diffractometer
Absorption correctionMulti-scan
SADABS, Bruker SHELXTL
Tmin, Tmax0.242, 0.438
No. of measured, independent and
observed [I > 2σ(I)] reflections
1395, 204, 200
Rint0.016
(sin θ/λ)max1)0.664
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.039, 0.093, 1.45
No. of reflections204
No. of parameters10
Δρmax, Δρmin (e Å3)0.69, 1.19

Computer programs: SMART (Bruker, 1997), SMART, SAINT (Bruker, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 1998), DIAMOND (Brandenburg, 2001).

Selected geometric parameters (Å, º) top
Ag1—O1i2.532 (5)Tc1—O11.724 (5)
Ag1—O1ii2.596 (5)
O1—Tc1—O1iii108.52 (16)O1iii—Tc1—O1iv111.4 (3)
Symmetry codes: (i) y+3/4, x+1/4, z+1/4; (ii) y1/4, x+1/4, z+1/4; (iii) y1/4, x+5/4, z+1/4; (iv) y+5/4, x+1/4, z+1/4.
Raman lines (cm−1) and assignments for pertechetate and perrhenate compounds top
Compoundν1ν3(E)ν3(B)
AgTcO4a880(v)e847(m)896(w)
[NH4][TcO4]b908(v)880(m)f
KTcO4c913(v)887(m)920(w)
AgReO4d942(v)862(m)899(w)
KReO4c966(v)897(m)924(w)
Notes: (a) this work; (b) Faggiani et al., 1980; (c) Busey & Keller, 1964; (d) Otto et al., 1991; (e) Relative intensity in parenthesis:- v = very strong, m = medium, w = weak; (f) This signal lies beneath the 908 signal (Faggiani et al., 1980).
 

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