X-ray crystallographic and first-principles theoretical studies of K 2[TcOCl5] and UV/Vis investigation of the [TcOCl 5]2- and [TcOCl4]- ions

Article abstract of DOI:10.1002/ejic.201201346

Dipotassium pentachloridooxidotechnetate, K₂[TcOCl₅], has been isolated as green single crystals by the dissolution of (NH ₄)TcO₄ in 12 M HCl at 0 °C and careful precipitation with KCl. The structure of this compound was determined by single-crystal X-ray diffraction analysis [a = 13.0815(9), b = 9.8982(6), c = 6.7623(4) A; V = 875.605 A³, orthorhombic, Pnma, Z = 4] and compared with the corresponding molybdenum and rhenium analogues. The structure of K ₂[TcOCl₅] was also investigated by density functional theory, and the results are in agreement with the crystallographic data. The oscillator strengths of the electronic transitions in the C_4v complex anions [TcOCl₅]^2- and [TcOCl₄]^- were also calculated by using time-dependent density functional theory and compared with the experimental UV/Vis spectra. Dipotassium pentachloridooxidotechnetate has been isolated as single crystals and its structure investigated by crystallographic and first-principles theoretical techniques. Copyright

Full text of DOI:10.1002/ejic.201201346

SHORT COMMUNICATION
DOI:10.1002/ejic.201201346
X-ray Crystallographic and First-Principles Theoretical
Studies of K [TcOCl ] and UV/Vis Investigation of the
2
5
2–
–
[
TcOCl ] and [TcOCl ] Ions
5
4
[
a]
[b]
[a]
Erik V. Johnstone,* Philippe F. Weck, Frederic Poineau,
[
c]
[a]
[a,d]
Eunja Kim, Paul M. Forster, Alfred P. Sattelberger,
Kenneth R. Czerwinski[
and
a]
Keywords: Technetium / Synthesis design / Density functional calculations / Structure elucidation / Radiopharmaceuticals
Dipotassium pentachloridooxidotechnetate, K
been isolated as green single crystals by the dissolution of
NH )TcO in 12 HCl at 0 °C and careful precipitation with
2
[TcOCl
5
], has
2 5
enum and rhenium analogues. The structure of K [TcOCl ]
was also investigated by density functional theory, and the
results are in agreement with the crystallographic data. The
oscillator strengths of the electronic transitions in the C4v
(
4
4
M
KCl. The structure of this compound was determined by sin-
2
–
–
gle-crystal X-ray diffraction analysis [a = 13.0815(9), b =
complex anions [TcOCl
5
]
4
and [TcOCl ] were also calcu-
3
9
.8982(6), c = 6.7623(4) Å; V = 875.605 Å , orthorhombic,
lated by using time-dependent density functional theory and
Pnma, Z = 4] and compared with the corresponding molybd- compared with the experimental UV/Vis spectra.
Introduction
rich coordination chemistry, which has been widely utilized
in the field of radiopharmaceuticals. Its short half-life
[
5]
2
–
Pentachloridooxidometallate(V)
[MOCl5]
complex
(t1/2 = 6 h) and energetically favorable γ decay energy (E =
γ
anions are formed with the transition metals V, Nb, Ta, Cr,
Mo, W, Tc, and Re. They can also be precipitated as crystal-
line salts with the heavier alkali metals (i.e., K, Rb, and Cs)
or other small monocationic counter ions, such as
99m
140 keV) make the metastable isotope
Tc an ideal im-
aging agent for diagnostic nuclear medicine. Macroscopic
manipulations of the pure β-emitting daughter isotope and
99
5
ground state Tc (t1/2 = 2.1ϫ10 years, E
= 0.3 MeV)
max
+
[1–4]
NH .
When precipitated as the caesium salt, these
4
allow for a better understanding of the fundamental chem-
istry of Tc, including structural and physical characteriza-
compounds crystallize in the cubic lattice with space group
Fm3m, whereas with K , Rb , or NH , the orthorhombic
Pnma structure is observed. Both the cubic and orthorhom-
bic structures are based on close-packing of the [MOCl5]
+
+
+
4
tions of the many inorganic and organometallic complexes
99m
used for body and organ imaging. Because
Tc is eluted
2–
99m
as Na TcO in isotope generators that separate techne-
tium from its parent nuclide (i.e., Mo, t1/2 = 66 h) by
4
[
1]
anions with the cations located in the tetrahedral holes.
99
The combination of the strong M=O interactions and
readily exchangeable chlorido ligands makes these six-coor-
dinate compounds important precursors to a variety of
polyatomic oxido-containing metal complexes. Technetium
means of column chromatography, typical syntheses of Tc
VII
radiopharmaceuticals start from Tc
pertechnetate solu-
tions. These solutions undergo “one-pot” reactions with a
specific ligand, reductant, and stabilizer to quickly and
(Z = 43) is a transition-metal element of particular interest,
99m
easily form low-valent
tion.
Tc complexes ready for injec-
primarily due to the synergy of its radiolytic properties and
[6–8]
Two easily synthesized, reduced-oxidation-state
species derived from pertechnetate, tetrachloridooxidotech-
–
[
a] Department of Chemistry, University of Nevada Las Vegas,
netate(V), [TcOCl ] , and pentachloridooxidotechnetate(V),
4
Las Vegas, NV 89154, USA
2–
[
TcOCl ] , are useful precursors for the synthesis of other
molecules with the Tc =O core.
5
Fax: +1-702-895-1907
V
[9–11]
E-mail: Erikvjohnstone@gmail.com
Homepage: http://radchem.nevada.edu/
b] Sandia National Laboratories,
Albuquerque, NM 87185, USA
n–
The preparation of salts of [TcOCl ] (x = 4, 5; n = 1,
x
[
[
–
VII
2
) entails the 2 e reduction of Tc
in cold concentrated
V
c] Department of Physics and Astronomy, University of Nevada HCl to the Tc intermediates, which must be isolated
Las Vegas,
Las Vegas, NV 89154, USA
relatively quickly to prevent further reduction to the ther-
[
d] Energy Engineering and Systems Analysis Directorate, Argonne modynamically very stable octahedral technetium(IV) com-
National Laboratory,
Argonne, IL 60439, USA
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201201346.
2–
plex, [TcCl ] . Solution studies have shown that both
6
V
Tc species are present in an equilibrium that favors the
monoanion {i.e., [TcOCl4] + Cl– w [TcOCl ] , k =
–
2–
5
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SHORT COMMUNICATION
(
1.5Ϯ1.0)ϫ10–3 m–1 in concentrated HCl at ambient Tc–Cl(4) and Tc–Cl(5). In comparison with the Tc–Cl link-
–
temperature}, but each can be selectively isolated according ages of square-pyramidal [TcOCl ] [i.e., av. Tc–Cl
4
to the size of the coordinating cation.[ The [TcOCl4]– 2.305(2)Å], those found in [TcOCl5] are 0.07(1) Å longer,
12]
2–
anion is isolated by precipitation using a large cation such a phenomenon observed for the Tc–X distances of five- and
+
+
+
[10,17]
as [Bu N] , [(C H ) As] , or [(Ph P) N] . Under the same six-coordinate structures.
Because of the structural
4
6
5 4
3
2
2
–
experimental conditions, six-coordinate [TcOCl5] has been trans effect (STE) of the oxido ligand, the single axial trans
isolated by using smaller monocations [i.e., M = K , Cs , Tc–Cl(2) bond [2.5389(9) Å; 2.57 Å by DFT] is significantly
NH , or N(CH CH ) ].
+
+
+
+ [12]
These complexes have been longer than those of the basal Tc–Cl linkages. In compari-
4
2
3 4
V
characterized by IR and Raman spectroscopy, magnetic son, the octahedral Tc =O-containing complex with the
measurements, and UV/Vis spectroscopy.[13–16] The solid- quadridentate Schiff-base ligand N,NЈ-propane-1,3-diylbis-
0
state structure of [(Ph P) N][TcOCl ] was determined by (salicylideneimine) (H salpd), that is, [TcOCl(salpd)] , exhib-
3
2
4
2
single-crystal X-ray diffraction (SCXRD), and – although its an axial trans Tc–Cl bond length of 2.44 Å, whereas for
no single crystal data for salts containing the [TcOCl5]2– Cs [Tc NCl ] the trans Tc–Cl bond is 2.740(5) Å long,
VI
2
5
anion have been reported – the salt Cs [TcOCl ] has been which demonstrates the increased influence of the opposing
2
5
characterized by powder XRD and EXAFS; it crystallizes axial triple-bonded Tc–N linkage in comparison with
with a cubic lattice.[
1,12,17]
The primary goal of this study Tc=O.
[20,21]
The trans Tc–Cl(2) linkage in K [TcOCl ] is one
2 5
was to isolate single crystals of the potassium salt of of the longest Tc–Cl bonds that has been reported for com-
2
–
V
[
TcOCl5] and to characterize its crystal structure by using pounds with a Tc =O core. Evidence for the distortion of
combined XRD and first-principles theoretical approaches. the six-coordinate octahedron is seen in the bond angles of
The spectral properties of the [TcOCl5] and [TcOCl4]– 94.9 and 82.4° (95.6 and 82.2° by DFT) for O–Tc–Cl(3) and
2–
complexes formed upon dissolution of the K [TcOCl ] salt Cl(4)–Tc–Cl(2), respectively, as well as for the O–Tc–Cl(2)
2
5
have also been investigated by UV/Vis spectroscopy and bond angle, which is slightly less than 180° (i.e., 178.7°;
time-dependent density functional theory (TD-DFT).
178.5° by DFT). The distortion displaces the Tc atom
slightly above (i.e., 0.248 Å) the equatorial plane of the cis-
Cl ligands towards the terminal O atom. The magnitude of
the displacement is similar to that noted for other octahe-
Results and Discussion
3+
[6]
dral (TcO) core complexes. The EXAFS data previously
Crystal Structure of Dipotassium Oxopentachlorotechnetate
[
12]
obtained
for Cs [TcOCl ] and the calculated DFT pa-
2 5
Dipotassium pentachloridooxidotechnetate(V) was iso- rameters are in close agreement with the structural param-
lated as green, hexagonal single crystals (Figure 1) by the eters determined by SCXRD (cf. Table 2). Atomic coordi-
reduction of NH TcO in cold concentrated HCl followed nates and additional structural parameters derived from
4
4
by slow precipitation with a solution of HCl saturated with XRD (see Table S1) and a polyhedral unit-cell packing dia-
KCl at 0 °C. Single-crystal analysis of K [TcOCl ] (Table 1) gram (see Figure S2) are provided in the Supporting Infor-
2
5
reveals a six-coordinate distorted octahedron that crys- mation.
tallizes in the orthorhombic Pnma space group with D2h
symmetry (IT No. 62) and unit-cell lattice parameters a =
1
8
3.0815(9), b = 9.8982(6), and c = 6.7623(4) Å (V =
75.605 Å , final R factor = 2.52%). The unit-cell param-
3
eters calculated by DFT are a = 13.55, b = 10.16, and c =
.98 Å, slightly larger than the experimentally determined
6
values owing to the well-known tendency of generalized
gradient approximation (GGA) functionals to overestimate
bond lengths. The computed ratios, b/a = 0.75 and c/a =
0
.51, are, however, in excellent agreement with the XRD
2
ratios, b/a = 0.7566 and c/a = 0.5169. The d complex is
isomorphous with two other early-transition-metal penta-
chloridooxidometallate salts K [MOCl ] (M
=
Mo,
2
5
Re),[
18,19]
with the “K [OsNCl ] structure type”. In the
2
5
[
TcOCl5]2– anion (Figure 2), the Tc=O bond length is
Figure 1. Optical microscopy image of
[TcOCl ].
a single crystal of
1
.634(3) Å (1.68 Å by DFT), which is similar to that found
K
2
5
V
in other octahedral Tc =O-containing compounds. There
are two different Tc–Cl linkages located cis and trans to the
The structural data for the technetium salt were com-
central Tc=O bond that are defined within the structure. pared with those of the molybdenum and rhenium ana-
The bonds of the three equatorial chlorine atoms cis Tc– logues (Table 3); the three salts show similar cis M–Cl bond
Cl(3,4,5) are significantly shorter [av. Tc–Cl 2.3763(7) Å; av. lengths. The largest difference between the three salts is ob-
Tc–Cl 2.40 Å by DFT] than the trans Tc-Cl bond. Of the served for the M=O bond and the corresponding relation-
four Cl atoms occupying the equatorial plane, the two sym- ship with the trans M–Cl bond; the stronger the M=O
metry-equivalent Tc–Cl(3) distances are slightly longer than bond, the longer the trans M–Cl distance, which is a direct
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SHORT COMMUNICATION
Table 1. Crystal data and refinement details for K
2
[TcOCl
5
].
Table 3. Interatomic distances [Å] in the
K
2
[MoOCl
],[18]
5
[21]
K
2
5 2 5
[TcOCl ], and K [ReOCl ]
crystals determined by single-crys-
Empirical formula Cl
5
K
2
OTc
tal X-ray diffraction analysis.
M
r
369.45
orthorhombic
Pnma
13.0815(9)
9.8982(6)
6.7623(4)
90
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α = β = γ [°]
V [Å ]
Z
Complex
[MoCl
[TcOCl
[ReOCl
M=O [Å]
av. M–Clcis [Å]
M–Cltrans [Å]
K
2
5
]
5
]
5
]
1.61(1)
1.634(3)
1.655(6)
2.386(6)
2.3763(7)
2.378(6)
2.587(6)
2.5389(9)
2.502(2)
K
2
K
2
3
875.60(10)
4
Molecular Structure and UV/Vis Spectroscopy of
2–
–
λ [Å]
μ [mm ] [Mo-K
0.71073
4.039
[TcOCl
5
]
and [TcOCl ]
4
–1
α
]
The dissolution of either (nBu N)[TcOCl ] or
F(000)
696
4
4
T [K]
θ range [°]
Independent reflections
Independent reflections with I Յ [2σ(I)]
Goodness-of-fit (F )
R1
wR2 [I Յ 2σ(I)]
100(2)
3.11–30.51
1409
1367
1.129
0.0252
0.0793
K [TcOCl ] in 12 m HCl at 0 °C yielded a greenish-yellow
2 5
solution. The UV/Vis spectra (cf. Figure S1 in the Support-
ing Information) of these solutions display analogous ab-
sorption maxima at around 230, 295, 475, 582, 882, 960,
and 1160 nm. The similarities between the two spectra are
indicative of the equilibrium formed between the two spe-
cies in HCl solution (see above).
2
To assign the bands observed in the UV/Vis spectra, ge-
ometry optimization of the [TcOCl5]2– and [TcOCl ] com-
–
4
plexes was performed by DFT followed by time-dependent
DFT (TD-DFT) calculations of the oscillator strengths and
2
–
transition energies associated with the relaxed [TcOCl ]
5
–
and [TcOCl ] complexes by using the Gaussian 09 software
4
22]
(
details are given in the Supporting Information).[ This
approach has been used successfully in previous studies on
[
23]
the speciation of technetium.
A study of the structural relaxation of the [TcOCl ]2–
5
complex at the GGA/B3LYP (GGA/PBE) level of theory
resulted in a C4v conformer with the following computed
bond lengths and angles: Tc–O 1.69 Å (1.70 Å), Tc–Cl3
2.49 Å (2.48 Å), Tc–Cl2 2.51 Å (2.51 Å), Cl3–Tc–Cl4 89.8°
(
(
89.8°), Cl2–Tc–Cl3 86.9° (86.7°), Cl3–Tc–Cl3 173.7°
173.3°), O–Tc–Cl2 180.0° (180.0°). These calculated bond
lengths and angles compare well with the results obtained
with VASP. The structural relaxation of the C -symmetric
]2– complex com-
5
posing the K [TcOCl ] crystal. Distances are in Å and angles in °.
2 5
4v
Figure 2. ORTEP representation of the [TcOCl
–
[
TcOCl ] complex analyzed at the GGA/B3LYP level of
4
theory resulted in the following bond lengths and angles:
Tc–O 1.67 Å, Tc–Cl3 2.40 Å, Cl3–Tc–Cl4 85.2°, Cl3–Tc–
Table 2. Interatomic distances determined by single-crystal X-ray Cl3 146.5°.
[
12]
The electronic structures of [TcOCl5]2– and [TcOCl ] re-
–
diffraction, EXAFS, and DFT for the K
2
[TcOCl
5
] crystal.
4
flect the C4v symmetry of these complexes with doubly de-
generate molecular orbitals (MOs) for the E representation
Method
XRD
EXAFS
DFT
Tc=O [Å]
av. Tc–Clcis [Å]
Tc–Cltrans [Å]
1.634(3)
1.65
1.68
2.3763(7)
2.36
2.40
2.5389(9)
2.50
2.57
[
a]
and nondegenerate MOs belonging to the A , A , B , or B
1 2 1 2
representations of this point group [cf. Figure 3 (top and
bottom)]. The HOMO–LUMO energy gaps calculated at
[
2 5
a] For Cs [TcOCl ].
2
–
the B3LYP/SDD level of theory for [TcOCl ]
and
5
–
[
TcOCl ] are 2.49 and 2.92 eV, respectively, that is, smaller
4
–
result of the STE. For technetium, the Tc=O distance is than the energy gap of TcO4 (5.15 eV), but significantly
slightly longer than that of the molybdenum complex, but larger than the gap of the hexahalogenidotechnetate(IV)
about 0.02(1) Å shorter than in the rhenium complex. complexes [TcX6]2– (X = Cl, Br; typically ca. 1–1.5 eV).
[24]
–
Transversely, as a result of the STE on the trans M–Cl dis- Note that the larger HOMO–LUMO gap of [TcOCl ] com-
4
tances, the molybdenum complex exhibits the longest trans pared with [TcOCl5]2– suggests a higher chemical stability
M–Cl distance (2.59 Å), which is approximately 0.06 and of this complex.
0
.09 Å longer than the technetium and rhenium trans M–
As shown in Figure 4 (top), the virtual molecular orbitals
Cl distances, respectively. The effect of the STE decreases (MOs) of the [TcOCl5]2– complex exhibit predominantly Tc
in the order Mo Ͼ Tc Ͼ Re.
4d characteristics, except for L+5 and L+6, which have
Eur. J. Inorg. Chem. 2013, 1097–1104
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SHORT COMMUNICATION
weak Tc 4d character, with some O 2p orbital contributions
LUMO, L+1, and L+3 to L+7) or some degree of Cl 3p
(
character (L+2, L+3, and L+5 to L+7). The HOMO pos-
sesses strong Tc 4dxy character with some contribution
from the Cl 3pxy orbitals, whereas MOs H–1 to H–10 are
essentially ligand-localized, with Cl 3p orbital contributions
(
(
H–1 to H–15) and, in some cases, some O 2p character
H–7 to H–12 and H–15). The lower-lying occupied MOs,
H–11 to H–15, feature a significant degree of Tc 4d charac-
ter. This combination of ligand-localized occupied MOs
and low-lying unoccupied MOs with marked Tc 4d charac-
ter points to ligand-to-metal charge transfer (LMCT), that
is, O 2pǞTc 4d or Cl 3pǞTc 4d transitions.
Figure 4. Top: Schematic representation of the highest-lying molec-
2
–
ular orbitals of the C4v-symmetric [TcOCl
5
]
complex calculated
at the B3LYP/SDD level of theory. Bottom: Schematic representa-
tion of the highest-lying molecular orbitals of the C4v-symmetric
–
[
TcOCl
4
] complex calculated at the B3LYP/SDD level of theory.
Color code: Tc, dark green; O, red; Cl, light green.
Figure 3. Top: Schematic energy-level diagram of the highest-lying
2–
molecular states of the C4v-symmetric [TcOCl
5
]
complex calcu-
lated at the B3LYP/SDD level of theory. The lowest unoccupied
molecular orbitals (LUMOs) are represented in blue and the high-
est occupied molecular orbitals (HOMOs) in red. The symmetry of
The highest-lying molecular orbitals of the [TcOCl ]–
4
each molecular orbital is indicated on the left. Bottom: Schematic complex are depicted in Figure 4 (bottom). There is a high
energy-level diagram of the highest-lying molecular states of the
–
degree of similarity between the [TcOCl ] MOs and those
4
–
C
4v-symmetric [TcOCl
level of theory. The lowest unoccupied molecular orbitals
LUMOs) are represented in blue and the highest occupied molecu-
4
]
complex calculated at the B3LYP/SDD
2–
of the [TcOCl5] complex discussed above. Therefore,
LMCT transitions are also expected to be dominant be-
lar orbitals (HOMOs) in red. The symmetry of each molecular or- tween ligand-localized occupied MOs and low-lying unoc-
(
bital is indicated on the left.
cupied MOs with marked Tc 4d character.
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SHORT COMMUNICATION
2
–
Oscillator strengths for the C -symmetric [TcOCl ]
4
v
5
–
and [TcOCl ] complexes calculated with TD-DFT at the
4
B3LYP/SDD level of theory are displayed in Figure 5 along
with the experimental UV/Vis spectrum of the species
formed upon dissolution of K [TcOCl ] in 12 m HCl at
2
5
0
°C. As expected for noncentrosymmetric complexes, nu-
merous electronic transitions are allowed. The experimental
absorption maxima at around 230, 295, 475, 582, and
9
60 nm are overall well reproduced by the positions of the
2–
computed oscillator strengths of the [TcOCl ]
and
5
–
[
TcOCl ] complexes. However, there are a few minor dis-
4
crepancies between the recorded UV/Vis spectrum and the
TD-DFT data: The low-intensity absorption bands ob-
served at around 882 and 1160 nm are not reproduced by
the calculations, and the computed oscillator strengths at
–
2–
3
79 nm for [TcOCl ] and 381 nm for [TcOCl ] do not ap-
4
5
pear in the UV/Vis spectrum. The residual discrepancies
subsisting between theory and experiment may be ascribed
to some extent to slight structural distortions of the anionic
complex in experiments compared with the ideal C4v sym-
metry used in the calculations and to the absence of explicit
treatment of the solvent in the calculations. Complete lists
of the transition energies and oscillator strengths for the
2
–
–
[
TcOCl5] and [TcOCl ] complexes with C symmetry are
2–
4
4v
4v 5
Figure 5. Oscillator strengths for the C -symmetric [TcOCl ] and
–
given in the Supporting Information (cf. Tables S2 and S3) [TcOCl ] complexes (red and green vertical bars, respectively) cal-
along with the compositions of individual excitations in
terms of major one-electron transitions between the molec-
ular orbital levels schematically represented in Figure 3 (top
and bottom, respectively).
4
culated with TD-DFT at the B3LYP/SDD level of theory. The ex-
2
–
–
perimental UV/Vis absorption spectrum of [TcOCl
5
] /[TcOCl
] in 12 m HCl at 0 °C (solid
blue line) is superimposed for comparison purpose.
4
]
2 5
formed by the dissolution of K [TcOCl
At short wavelengths, the most intense oscillator
2
–
strengths of the [TcOCl5] complex are found at 214 nm 0.0187; H–4Ǟ[LUMO, L+1] (98%)}. At longer wave-
–
{
intensity: 0.0839; [H–8, H–9]ǞL+4 (34%), H–1Ǟ[L+5, lengths, two transitions of the [TcOCl ] complex are pre-
4
L+6] (32%), [H–2, H–3]ǞL+7 (20%), [H–11, H–12]ǞL+2 dicted at 502 nm {intensity: 0.0002; H–1Ǟ[LUMO, L+1]
10%)}, 221 nm {intensity: 0.0687; H–7ǞL+4 (86%)}, (100%)} and 977 nm {intensity: 0.0001;
22 nm {intensity: 0.0721; [H–8, H–9]ǞL+3 (38%), [H–8, [HOMO]Ǟ[LUMO, L+1] (100%)}. The latter coincides
H–9]ǞL+4 (30%), [H–11, H–12]ǞL+2 (20%)}, 234 nm with the absorption maximum observed at 960 nm.
(
2
2
–
{
0
intensity: 0.0985; H–7ǞL+3 (92%)}, 243 nm {intensity:
In noncentrosymmetric complexes such as [TcOCl ]
5
–
.0909; [H–4, H–5](E)ǞL+3 (60%), HOMOǞ[L+5, L+6] and [TcOCl ] with C point-group symmetry, transitions
4
4v
(
(
38%)}, 276 nm {intensity: 0.0326; [H–8, H–9]ǞL+2 will be allowed only for certain orientations of the electric
82%)}, and 293 nm {intensity: 0.0151; [H–11, H– vector of the incident light, and pure electronic selection
12]Ǟ[LUMO, L+1] (84%)}. The oscillator strengths at 234 rules might be expected to apply strictly. A detailed analysis
and 293 nm are in very good agreement with the absorption of the polarization of the one-electron transitions compos-
maxima at 230 and 295 nm, respectively. At longer wave- ing the various bands calculated with TD-DFT is helpful
lengths, predicted oscillator strengths are located at 381 nm for understanding the UV/Vis spectrum recorded experi-
{
4
4
4
intensity: 0.0339; [H–8, H–9]Ǟ[LUMO, L+1] (84%)}, mentally.
51 nm {intensity: 0.0241; H–7Ǟ[LUMO, L+1] (74%)},
In the C4v symmetry, the polarization of the following
67 nm {intensity: 0.0012; H–6Ǟ[LUMO, L+1] (76%)}, types of allowed transitions needs to be determined: EǞE,
77 nm {intensity: 0.0076; [H–4, H–5]Ǟ[LUMO, L+1] EǞB , EǞA , A ǞA , B ǞE, A ǞE, A ǞE, B ǞB ,
2
1
1
1
1
2
1
2
2
(
84%)}, 492 nm {intensity: 0.0161; [H–2, H–3]Ǟ[LUMO, and B ǞE. In the C point group, z belongs to the A1
2 4v
L+1] (80%)}, and 583 nm {intensity: 0.0002; H– representation and x,y to the E representation. The results
Ǟ[LUMO, L+1] (100%)}. The experimental bands cen- for the irreducible representations spanned by the dipole
tered at 475 and 582 nm are well reproduced by the oscil- integrals ͐ψЈ zψ dτ and ͐ψЈ (x,y)ψ dτ for each of the nine
1
e
e
e
e
lator strengths at 477 and 583 nm, respectively.
transition types listed above are reported in Table 4. Analy-
At short wavelengths, the most intense oscillator sis of these results shows that the only allowed one-electron
–
strengths of the [TcOCl ] complex with C symmetry are transitions for z-polarized incident radiation are the EǞE,
4
4v
located at 220 nm {intensity: 0.0289; H–12Ǟ[LUMO, L+1] A ǞA , and B ǞB transitions, whereas the remaining
1
1
2
2
(
(
72%)}, 250 nm {intensity: 0.0270; [H–5, H–6]ǞL+2 EǞB , EǞA , B ǞE, A ǞE, A ǞE, and B ǞE transi-
36%), [H–5, H–6]ǞL+3 (28%)}, and 379 nm {intensity: tions are only allowed for the x,y-polarized incident radia-
2 1 1 2 1 2
Eur. J. Inorg. Chem. 2013, 1097–1104
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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SHORT COMMUNICATION
Table 4. Irreducible representations spanned by the dipole integrals ͐ψЈ
zψ
e e
dτ and ͐ψЈ
e
(x,y)ψ
e
dτ for the one-electron transitions compos-
ing the various bands calculated with TD-DFT.
Transition
͐ψЈ zψ
e e
dτ
͐ψЈ
e
(x,y)ψ
e
dτ
Polarization of incident radiation
z
x,y
EǞE
A
1
+A
2
+B
E
E
1
+B
2
4E
allowed
forbidden
EǞB
EǞA
ǞA
ǞE
2
A
A
1
+A
+A
2
+B
+B
1
+B
+B
2
forbidden
forbidden
allowed
forbidden
forbidden
forbidden
allowed
allowed
allowed
forbidden
allowed
allowed
allowed
forbidden
allowed
1
1
2
1
2
A
1
1
A
E
E
E
1
E
B
A
A
1
A
1
A
1
A
1
+A
+A
+A
2
+B
+B
+B
1
1
1
+B
+B
+B
2
2
2
2
ǞE
ǞE
2
2
1
B
B
2
ǞB
ǞE
2
A
E
1
E
2
A
1
+A
2
+B
1
+B
2
forbidden
2–
tion. This suggests that the optically active [TcOCl ] and TD-DFT and correlated with the absorption peaks in the
5
–
[
TcOCl4] complexes will exhibit differing absorption of experimental UV/Vis spectrum. To date, K [TcOCl ] is the
2 5
light polarized along the directions parallel or perpendicu- only K [TcOX ] complex that has been reported crystallo-
2
5
lar to the z axis (coinciding with the C axis of the anion), graphically by using SCXRD. Therefore, it would be of
4
that is, dichroism. This could be verified, for example, by interest to isolate and study the other [TcOX5]2– (X = F, Br,
using standard linear dichroism spectroscopic techniques.
I) complexes and compare these with the Cl complex. In
From the compositions of the bands calculated for the addition, because of the popularity of the five-coordinate
2
–
–
[
TcOCl5] complex with TD-DFT (cf. Table S5 in the Sup- [TcOCl ] as a precursor for radiopharmaceuticals contain-
4
porting Information), it can be seen that only six are com- ing the (TcO)3 core, and structural differences and behav-
+
posed of pure combinations of allowed one-electron transi- ior, K [TcOCl ] serves as a similar but different potential
2
5
tions for z-polarized incident radiation, that is, the bands at starting material for radiopharmaceuticals.
21 nm (A ǞA ; intensity: 0.0687), 234 nm (A ǞA ; inten-
2
1
1
1
1
sity: 0.0985), 293 nm (EǞE and B ǞB ; intensity: 0.0151),
2
2
3
0
81 nm (EǞE; intensity: 0.0339), 477 nm (EǞE; intensity:
Experimental Section
.0076), and 492 nm (EǞE; intensity: 0.0161). For the
–
CAUTION! Techetium-99 is a weak β emitter (Emax = 292 keV).
All manipulations were performed in a laboratory designed for
work with radionuclides by using efficient HEPA-filtered fume
hoods, Schlenk and glove-box techniques, and applying locally ap-
proved radiochemistry handling and monitoring procedures. Labo-
ratory coats, disposable gloves, and protective eyewear were worn
at all times.
[
TcOCl ] complex (cf. Table S3 in the Supporting Infor-
4
mation), only five computed bands are composed of pure
combinations of allowed one-electron transitions for z-pola-
rized incident radiation: at 214 nm (EǞE, A ǞA , and
B ǞB ; intensity: 0.0043), 246 nm (EǞE and A ǞA ; in-
tensity: 0.0039), 280 nm (B ǞB ; intensity: 0.0003), 342 nm
1
1
2
2
1
1
2
2
(EǞE; intensity: 0.0038), and 388 nm (EǞE; intensity:
2–
Reagents: Technetium was purchased from Oak Ridge National
Laboratory as NH TcO and used as received. All other reagents
4 4
were purchased from Sigma–Aldrich and used as received.
0
.0003). All the other computed bands for the [TcOCl ]
5
–
and [TcOCl ] complexes are composed of pure combina-
tions of allowed one-electron transitions for x,y-polarized
incident radiation.
4
Preparation of Dipotassium Pentachloridooxidotechnetate(V):
NH TcO (50.6 mg, 0.280 mmol) was placed in a glass scintillation
4 4
vial, and cold (0 °C) 12 m HCl (3 mL) was added. The vial was
capped and lightly agitated for 10 min during which time the flask
was periodically vented of the Cl gas formed. After the reaction,
2
Conclusions
K [TcOCl ] has been isolated and characterized crystal- all of the solids had dissolved to yield a dark-green solution. A
2
5
saturated solution of KCl (450 mg) in 12 m HCl (3 mL) was layered
on top of the green liquid and placed in a freezer at –23 °C for
single-crystal growth. After approximately 24 h, small, transparent
green hexagonal crystals crystallized from the solution (ca. 3 mg).
The identity of the compound was confirmed by UV/Vis spec-
troscopy (see Figure S1 in the Supporting Information).
lographically and by first-principles theoretical calculations.
It is the first single-crystal characterization of the
2
–
[
TcOCl5] species. Its structure exhibits an axial Tc=O
bond and a correlated elongated trans Tc–Cl bond attrib-
uted to the STE, as well as four basal Cl atoms in the equa-
torial plane from which the central Tc atom is vertically
displaced. The structure of the Tc complex was compared
with those of the isostructural Re and Mo complexes, which
showed that the STE decreases in the order Mo Ͼ Tc Ͼ
Re. The results of the DFT calculations are in agreement
with the structural parameters determined by XRD analy-
sis. The MO diagram shows contributions from Tc 4d, Cl
Single-Crystal X-ray Diffraction Analysis: Data were collected with
a Bruker Apex II system equipped with an Oxford nitrogen cryo-
stream operating at 100 K. Crystals were mounted under Paratone
on a glass fiber. Data processing was performed by using the Apex
[25]
II suite and an absorption correction applied with SADABS.
Structure determination (direct methods) and refinement were car-
[26,27]
ried out by using SHELX97 and Olex2.
Further details of the
3p, and O 2p orbitals, and the HOMO–LUMO energy gap crystal structure investigation may be obtained from the Fachinfor-
was determined. Oscillator strengths were calculated with mationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Ger-
Eur. J. Inorg. Chem. 2013, 1097–1104
1102
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
SHORT COMMUNICATION
many (fax: +49-7247-808-666; e-mail: crysdata@fiz-karlsruhe.de), aged and operated by Sandia Corporation, a wholly owned subsid-
on quoting the depository number CSD-425683.
iary of Lockheed Martin Corporation, for the U.S. Department of
Energy’s National Nuclear Security Administration under contract
DE-AC04-94AL85000.
Crystal Structure from First-Principle Calculations: First-principles
total energy calculations for the K [TcOCl ] crystal were performed
2 5
by using spin-polarized density functional theory (DFT) as im-
plemented in the Vienna ab initio simulation package (VASP).[
28]
[1] J. E. Fergusson, A. M. Greenway, B. R. Penfold, Inorg. Chim.
Acta 1983, 71, 29–34.
The exchange-correlation energy was calculated by using the gener-
alized gradient approximation (GGA) with Perdew–Burke–Ernzer-
[
[
[
[
[
2] W. F. Jackob, B. Z. Jezowska, Z. Anorg. Chem. 1933, 214, 337.
3] D. J. Brown, J. Chem. Soc. 1964, 4944.
[29]
hof (PBE) parametrization. Pure functionals, such as the PBE or
4] D. A. Edwards, R. T. Ward, J. Mol. Struct. 1970, 6, 421.
5] B. Johannsen, H. Spies, Top. Curr. Chem. 1996, 176, 77.
6] K. Schwochau in Technetium: Chemistry and Radiopharmaceu-
tical Applications, Wiley-VCH, Weinheim, 2000, pp. 165–380.
[
30]
Perdew–Wang (PW91) functionals, have been found in previous
studies to correctly describe the geometric parameters and proper-
ties of various technetium halide crystals observed experimen-
[
31–34]
tally.
[7] U. Abram, R. Alberto, J. Braz. Chem. Soc. 2006, 17, 1486.
[
[
8] H. Braband, Chimia 2011, 65, 776.
The interaction between valence electrons and ionic cores was de-
9] A. Davison, A. G. Jones, Int. J. Appl. Radiat. Isot. 1982, 33,
[
35,36]
scribed by the projector-augmented wave (PAW) method.
4
Tc
875.
6
2
5
6
1
2
5
2
4
p 5s 4d , K 3p 4s , Cl 3s 3p , and O 2s 2p electrons were treated
[10] G. Bandoli, U. Mazzi, E. Roncari, E. Deutsch, Coord. Chem.
explicitly as valence electrons in the Kohn–Sham (KS) equations,
and the remaining core electrons together with the nuclei were rep-
resented by PAW pseudopotentials. The KS equations were solved
by using the special blocked Davidson iterative matrix diagonaliza-
Rev. 1982, 44, 191.
[11] R. W. Thomas, A. Davison, H. S. Trop, E. Deutsch, Inorg.
Chem. 1980, 19, 2840.
[
[
[
[
[
[
[
12] R. W. Thomas, M. J. Heeg, R. C. Elder, E. Deutsch, Inorg.
[
37]
Chem. 1985, 24, 1472.
13] B. Jezowska-Trzebiatowska, S. Wajda, M. Baluka, Zh. Strukt.
Khim. 1967, 8, 524.
14] M. Baluka, J. Hanuza, B. Jezowska-Trzebiatowska, Bull. Acad.
Polon. Sci. 1972, 20, 271.
15] J. Hanuza, M. Baluka, B. Jezowksa-Trzebiatowska, Acta Phys.
Polon. 1987, A71, 91.
16] B. Jezowska-Trzebiatowska, M. Baluka, Bull. Acad. Polon. Sci.
tion scheme.
The plane-wave cutoff energy for the electronic
wavefunctions was set to a value of 500 eV, ensuring the total en-
ergy of the system to be converged to within 1 meV/atom. Partial
occupancies were set for each wavefunction by using the tetrahe-
dron method with Blöchl corrections.[
38]
Ionic relaxation was carried out by using the conjugate gradient
algorithm and the Hellmann–Feynman forces acting on atoms were
calculated with a convergence tolerance set to 0.01 eV/Å. A per-
iodic unit cell approach was used in the calculations. In structural
relaxation calculations, the structure determined by XRD was used
as the starting geometry, and no symmetry constraints were applied
1975, 13, 1.
17] F. A. Cotton, A. Davison, V. W. Day, L. D. Gage, H. Trop, In-
org. Chem. 1979, 18, 3024.
18] V. V. Tkachev, O. N. Krasochka, L. O. Atovmyan, Zh. Strukt.
Khim. 1976, 17, 940.
during relaxation. The Brillouin zone was sampled by using the
[19] T. Glowiak, B. Jezowska-Trzebiatowska, T. Lis, Acta Crys-
tallogr., Sect. C 1991, 47, 177.
Monkhorst–Pack k-point scheme[
39]
with a k-point mesh of
[
20] J. Baldas, S. F. Colmanet, Inorg. Chim. Acta 1991, 179, 189.
21] G. Bandoli, M. Nicolini, U. Mazzi, F. Refosco, J. Chem. Soc.,
Dalton Trans. 1984, 2505.
3
ϫ5ϫ5.
[
Other Techniques: UV/Vis spectra were recorded at room tempera-
ture in a quartz cell (1 cm) with a Cary 6000i double-beam spec-
trometer. Concentrated HCl was used as the reference. In addition,
to assign the spectral signatures observed in the recorded UV/Vis
spectrum, DFT calculations of the structural optimization of the
[22] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li,
H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-
nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-
gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M.
Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Starov-
erov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,
J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M.
Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Ad-
amo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Mar-
tin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B.
Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09, Re-
vision A.02, Gaussian, Inc., Wallingford, CT, 2009.
2–
[
TcOCl
5
]
anion followed by TD-DFT calculations of the oscil-
lator strengths and transition energies associated with the relaxed
complex were carried out by using the Becke 3-parameter, Lee–
[
40–43]
Yang–Parr
(B3LYP) hybrid functional, the Dunning–Huzin-
[44]
aga valence double-zeta basis set
(D95V), and the Stuttgart/
Dresden effective core potentials[ (SDD) with the Gaussian 09
software (details of the calculations are provided in the Supporting
Information).
45]
[22]
Supporting Information (see footnote on the first page of this arti-
cle): Computational method, transition energies, and oscillator
2–
strengths for the [TcOCl
5
]
anion computed with TD-DFT.
[
23] F. Poineau, P. F. Weck, K. German, A. Maruk, G. Kirakosyan,
W. W. Lukens, D. B. Rego, A. P. Sattelberger, K. R. Czerwinski,
Dalton Trans. 2010, 39, 8616.
Acknowledgments
[
[
24] P. F. Weck, E. Kim, K. R. Czerwinski, Chem. Phys. Lett. 2010,
487, 190.
The authors would like to thank Julie Bertoia and Trevor Low for
outstanding laboratory management and health physics support.
Funding for this project was supported by the Department of En-
ergy under the SISGR-Fundamental Chemistry of Technetium-99
Incorporated into Metal Oxide, Phosphate and Sulfide: Toward
Stabilization of Low-Valent Technetium (Contract No. 47824B)
25] Bruker, SADABS, Bruker AXS Inc., Madison, Wisconsin,
USA, 2001.
[
[
26] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
27] O. V. Dolmanov, R. J. Gildea, J. A. K. Howard, H. Puschmann,
J. Appl. Crystallogr. 2009, 42, 339.
[
28] G. Kresse, J. Furthmüller, Phys. Rev. B 1996, 54, 11169.
and the U.S. Department of Energy Award (No. DE-SC00052). [29] P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77,
Sandia National Laboratories is a multi-program laboratory man-
1103
3865.
Eur. J. Inorg. Chem. 2013, 1097–1104
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
SHORT COMMUNICATION
[
[
30] J. P. Perdew, Y. Wang, Phys. Rev. B 1992, 45, 13244.
[38] P. E. Blöchl, O. Jepsen, O. K. Andersen, Phys. Rev. B 1994, 49,
31] F. Poineau, E. Johnstone, P. F. Weck, P. M. Forster, E. Kim,
K. R. Czerwinski, A. P. Sattelberger, Inorg. Chem. 2012, 51,
16223.
[
[
[
39] H. J. Monkhorst, J. D. Pack, Phys. Rev. B 1976, 13, 5188.
40] A. D. Becke, J. Chem. Phys. 1993, 98, 5648.
41] C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785.
4915.
[
[
[
32] F. Poineau, C. D. Malliakas, P. F. Weck, B. L. Scott, E. V. John-
stone, P. M. Forster, E. Kim, M. G. Kanatzidis, K. R. Czerwin-
ski, A. P. Sattelberger, J. Am. Chem. Soc. 2011, 133, 8814.
33] F. Poineau, E. V. Johnstone, P. F. Weck, E. Kim, P. M. Forster,
B. L. Scott, A. P. Sattelberger, K. R. Czerwinski, J. Am. Chem.
Soc. 2010, 132, 15864.
34] P. F. Weck, E. Kim, F. Poineau, E. Rodriguez, A. P. Sattel-
berger, K. R. Czerwinski, Inorg. Chem. 2009, 48, 6555.
35] P. E. Blöchl, Phys. Rev. B 1994, 50, 17953.
[42] S. H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 1980, 58, 1200.
[43] P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J.
Phys. Chem. 1994, 98, 11623.
[44] T. H. Dunning Jr., P. J. Hay in Modern Theoretical Chemistry
(Ed.: H. F. Schaefer III), Plenum Press, New York, 1976, vol.
3, pp. 1–28.
[
[
[
[45] D. Andrae, U. Haeussermann, M. Dolg, H. Stoll, H. Preuss,
Theor. Chem. Acc. 1990, 77, 123.
36] G. Kresse, D. Joubert, Phys. Rev. B 1999, 59, 1758.
37] E. R. Davidson in Methods in Computational Molecular Phys-
ics (Eds.: G. H. F. Diercksen, S. Wilson), Reidel Publishing
Company, Dordrecht, 1983, vol. 113, p. 95.
Received: November 9, 2012
Published Online: January 23, 2013
Eur. J. Inorg. Chem. 2013, 1097–1104
1104
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim