Hexa­carbonyl­technetium(I) perchlorate

The title compound, [Tc(CO)₆]ClO₄, was synthesized by the reaction of [TcCl(CO)₅] with AgClO₄, followed by acidification with HClO₄ under a CO atmosphere. The [Tc(CO)₆]⁺ cation has close to idealized octa­hedral geometry, with the bond angles between cis-CO groups close to 90° and the Tc—C bond lengths in the range 2.025 (3)–2.029 (3)Å. The perchlorate anion is disordered over two crystallographically equivalent half-occupied positions. The Tc atom in the [Tc(CO)₆]⁺ cation is located on an inversion centre.

Related literature

For the first report on the [Tc(CO)₆]⁺ cation, see: Hieber et al. (1965). For related literature, see: Aebischer et al. (2000); Alberto et al. (1996, 1998); Baturin et al. (1994a,b); Grigor'ev et al. (1997a,b); Miroslavov et al. (2008a,b); Schwochau (2000).

Experimental

Crystal data

• [Tc(CO)₆]ClO₄

• M_r = 366.42

• Monoclinic, C 2/c

• a = 13.227 (4) Å

• b = 6.8002 (18) Å

• c = 13.616 (3) Å

• β = 112.56 (2)°

• V = 1131.0 (5) ų

• Z = 4

• Mo Kα radiation

• μ = 1.55 mm⁻¹

• T = 293 (2) K

• 0.20 × 0.18 × 0.10 mm

Data collection

• Stoe IPDS-2 diffractometer

• Absorption correction: integration (X-RED and X-SHAPE; Stoe & Cie, 2005) T_min = 0.620, T_max = 0.723

• 4935 measured reflections

• 1508 independent reflections

• 1224 reflections with I > 2σ(I)

• R_int = 0.035

Refinement

• R[F² > 2σ(F²)] = 0.030

• wR(F²) = 0.067

• S = 1.06

• 1508 reflections

• 99 parameters

• Δρ_max = 0.32 e Å⁻³

• Δρ_min = −0.44 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2007); cell refinement: X-AREA; data reduction: X-RED (Stoe & Cie, 2005); program(s) used to solve structure: SHELXL97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2000); software used to prepare material for publication: publCIF (Westrip, 2008).

Supporting information

S1. Comment

Among technetium(I) carbonyl complexes, the highest carbonyl, [Tc(CO)₆]⁺ cation, is the least studied compared to penta-, tetra-, and especially tricarbonyl complexes (Schwochau, 2000). No data on the crystal structure of its salts are available. More detailed study of this cation is significant for the development of the coordination chemistry of technetium (and d block as a whole). The first report on the [Tc(CO)₆]⁺ cation is dated by Hieber et al., 1965 prepared this species in the form of the solid compound [Tc(CO)₆][AlCl₄] by the solid-phase reaction of [TcCl(CO)₅] with AlCl₃ under high CO pressure (300 atm) at 363 K (Heiber et al., 1965). The product was characterized by chemical analysis, and the cation appeared to be stable in solutions. Relatively recently (Aebischer et al., 2000) observed successive formation of higher technetium carbonyls [Tc(CO)_n(H₂O)_6–n]⁺ (n = 4–6) in aqueous solution (2 M HClO₄) from the complex [Tc(CO)₃(H₂O)₃]⁺ at room temperature and moderately high CO pressure (about 50 atm), after removal of chloride ions. The reaction progress was monitored by the ⁹⁹Tc and ¹³C NMR. The relative content of the [Tc(CO)₆]⁺ cation in the mixture of technetium carbonyl species was low, and no solid salt of this cation was isolated. Here we report on the synthesis and crystal structure of hexacarbonyltechnetium(I) perchlorate, [Tc(CO)₆]ClO₄.

Related literature

For the first report on the [Tc(CO)₆]⁺ cation, see: Hieber et al. (1965). For related literature, see: Aebischer et al. (2000); Alberto et al. (1996, 1998); Baturin et al. (1994a,b); Grigor'ev et al. (1997a,b); Miroslavov et al. (2008a,b); Schwochau (2000).

S2. Experimental

Pentacarbonyltechnetium chloride [TcCl(CO)₅] (SU Inventor's Certificate 1512003) was dissolved in boiled water, and a stoichiometric amount of AgClO₄ was added after cooling to remove chloride ions interfering with the synthesis (Miroslavov et al., 2008a). The resulting solution was acidified with HClO₄ to a concentration of 2 M and treated with CO in a pressure vessel (443 K, 150 atm, 1 h). After completing the reaction and removing the excess of CO, the reaction system consisted of an aqueous solution and a colorless crystalline precipitate. The precipitate was separated, washed with water and methylene chloride (to remove an impurity of [TcCl(CO)₅] (Miroslavov et al., 2008a)), and dried in air. The product was identified as [Tc(CO)₆]ClO₄. Some of the crystals appeared to be suitable for an X-ray diffraction analysis. ⁹⁹Tc NMR(CH₃OH): -1924 p.p.m.. IR (CH₃CN): n_CO 2095 cm^-1. Found Tc, %: 27.12. C₆ClO₁₀Tc. Calculated Tc, %: 27.01. The IR spectrum was recorded on a Shimadzu FTIR 8700 spectrophotometer. The ⁹⁹Tc NMR spectrum was taken on a Bruker WP-200 spectrometer.

S3. Refinement

The crystal structure of [Tc(CO)₆]ClO₄ contains one symmetrically independent Tc⁺ cation octahedrally coordinated by six carbon atoms (Figs. 1, 2). The Tc—C=O fragments are linear to within 3°. The coordination polyhedron of technetium in the [Tc(CO)₆]⁺ cation is close to an ideal octahedron, with the bond angles between cis-CO groups equal to 90° (within ±1.5°) and the Tc–C bond lengths in the range of 2.025–2.029 Å. These distances are significantly (by 0.1–0.15 Å) longer than the Tc–C distances in trans-OC–Tc–σ donor fragments, e.g.: [TcI(CO)₅](Tc–C_trans-I) 1.938 (Grigor'ev et al., 1997a), [TcI(CO)₄]₂ (Tc–C_trans-I) 1.89–1.92 (Grigor'ev et al., 1997b), [TcCl(CO)₃]₄ 1.903 (Baturin et al., 1994a), [TcBr(CO)₃(en)] 1.882–1.889 (Baturin et al., 1994b), [Tc(OH)(CO)₃]₄ 1.886–1.905 Å (Alberto et al., 1998). At the same time, they are only slightly longer than the Tc–C distances in trans-OC–Tc–π acceptor fragments of other structurally examined complexes (π acceptor is another CO group, PPh₃, or Bu^tNC): [Tc(CO)₅(Bu^tNC)]ClO₄ 1.999–2.022 (Miroslavov et al., 2008b), [Tc(CO)₅(PPh₃)]CF₃SO₃ 1.985–2.019 (Alberto et al., 1998) (in these two compounds, the lengths of the equatorial and axial Tc–CO bonds are similar), [fac-Tc(CO)₃(Bu^tNC)₃]NO₃ 1.963–1.975 (Alberto et al., 1996) [TcI(CO)₅] (Tc–C~trans-CO~) 2.015 (Grigor'ev et al., 1997a), [TcI(CO)₄]₂ (Tc–C_trans-CO) 1.98–2.01 Å (Grigor'ev et al., 1997b). The large difference between the Tc–CO bond lengths in cases when the transposition to the CO group is occupied by a π acceptor or a σ donor can be attributed to the trans effect (competition between the π acceptors arranged trans to each other for the same occupied d orbital of the metal ion). A certain cis effect, however, also takes place, because the Tc–CO bonds in the [Tc(CO)₆]⁺ cation are somewhat longer than the Tc–CO bonds in trans-OC–Tc–CO fragments of complexes containing in cis positions ligands that are σ donors or π acceptors weaker than CO.

The Cl atom in the structure of [Tc(CO)₆]ClO₄ is tetrahedrally coordinated by four O atoms (mean Cl–O distance is 1.403 Å). The perchlorate anion is disordered over two crystallographically equivalent half-occupied positions (Fig. 2) with the total site-occupation factor (s.o.f.) equal to 1.0. The central atoms of [Tc(CO)₆]⁺ octahedra and [ClO₄]^- tetrahedra (Tc and Cl respectively) form a distorted NaCl-type lattice oriented along a_NaCl [110], b_NaCl [10–1], c_NaCl [-110] (Fig. 3).

Computing details

Data collection: X-AREA (Stoe & Cie, 2007); cell refinement: X-AREA (Stoe & Cie, 2007); data reduction: X-RED (Stoe & Cie, 2005); program(s) used to solve structure: SHELXL97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2000); software used to prepare material for publication: publCIF (Westrip, 2008).

Figures

	Fig. 1. View of the [Tc(CO)6]^+cation (a) and one component of the disordered perchlorate anion (b) in the structure of [Tc(CO)6]ClO4. Thermal ellipsoids are drawn at the 50% probability level.
	Fig. 2. Crystal structure of [Tc(CO)6]ClO4. Tc atoms are dark-grey, O atoms are grey, Cl atoms are light-grey, and C atoms are white circles.
	Fig. 3. Relationship of title structure to NaCl structure.

Hexacarbonyltechnetium(I) perchlorate

Crystal data

[Tc(CO)6]ClO4	F(000) = 704
Mr = 366.42	Dx = 2.152 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 5446 reflections
a = 13.227 (4) Å	θ = 2.0–29.6°
b = 6.8002 (18) Å	µ = 1.55 mm^−1
c = 13.616 (3) Å	T = 293 K
β = 112.56 (2)°	Prism, colorless
V = 1131.0 (5) Å^3	0.20 × 0.18 × 0.10 mm
Z = 4

Data collection

Stoe IPDS-2 diffractometer	1508 independent reflections
Radiation source: fine-focus sealed tube	1224 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.035
Detector resolution: 6.67 pixels mm^-1	θmax = 29.2°, θmin = 3.2°
rotation method scans	h = −18→18
Absorption correction: integration (X-RED and X-SHAPE; Stoe & Cie, 2005)	k = −9→8
Tmin = 0.620, Tmax = 0.723	l = −18→18
4935 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.031	w = 1/[σ^2(Fo^2) + (0.0289P)^2 + 1.543P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.067	(Δ/σ)max < 0.001
S = 1.06	Δρmax = 0.32 e Å^−3
1508 reflections	Δρmin = −0.44 e Å^−3
99 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0043 (12)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Tc1	0.2500	0.2500	0.0000	0.03673 (14)
C1	0.2509 (2)	0.1350 (5)	0.1375 (2)	0.0484 (7)
C2	0.3021 (2)	−0.0119 (5)	−0.0345 (2)	0.0446 (6)
C3	0.4088 (2)	0.3328 (5)	0.0721 (3)	0.0501 (7)
O1	0.3312 (2)	−0.1557 (4)	−0.0529 (2)	0.0632 (6)
O2	0.49658 (19)	0.3762 (4)	0.1078 (3)	0.0774 (8)
O3	0.2481 (2)	0.0685 (5)	0.2111 (2)	0.0778 (8)
O4	0.0932 (2)	−0.2268 (5)	−0.1933 (3)	0.0814 (9)
O5	0.503 (3)	0.0179 (9)	0.2724 (16)	0.109 (7)	0.50
O6	0.5401 (5)	−0.1423 (12)	0.1398 (5)	0.0856 (18)	0.50
Cl1	0.50996 (15)	−0.1697 (2)	0.22853 (14)	0.0480 (4)	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Tc1	0.03421 (17)	0.04318 (19)	0.03316 (17)	0.00255 (14)	0.01331 (11)	−0.00340 (15)
C1	0.0481 (15)	0.0592 (18)	0.0423 (16)	0.0126 (13)	0.0222 (12)	0.0041 (13)
C2	0.0403 (13)	0.0519 (15)	0.0404 (14)	0.0037 (12)	0.0141 (11)	−0.0028 (12)
C3	0.0418 (14)	0.0527 (15)	0.0545 (18)	0.0005 (13)	0.0172 (13)	−0.0074 (14)
O1	0.0693 (15)	0.0567 (14)	0.0658 (16)	0.0148 (12)	0.0284 (12)	−0.0076 (12)
O2	0.0433 (12)	0.0782 (18)	0.105 (2)	−0.0091 (12)	0.0216 (13)	−0.0225 (16)
O3	0.0830 (18)	0.105 (2)	0.0609 (16)	0.0297 (16)	0.0444 (14)	0.0249 (16)
O4	0.0566 (14)	0.096 (2)	0.087 (2)	−0.0202 (14)	0.0229 (14)	−0.0261 (16)
O5	0.077 (4)	0.074 (3)	0.155 (19)	−0.002 (8)	0.021 (12)	−0.052 (8)
O6	0.072 (3)	0.120 (5)	0.061 (3)	−0.019 (3)	0.021 (3)	0.019 (4)
Cl1	0.0366 (7)	0.0512 (6)	0.0497 (12)	−0.0023 (6)	0.0094 (6)	−0.0015 (6)

Geometric parameters (Å, º)

Tc1—C1^i	2.025 (3)	O5—O5^iv	0.59 (4)
Tc1—C1	2.025 (3)	O5—Cl1^iv	1.286 (8)
Tc1—C3^i	2.027 (3)	O5—Cl1	1.428 (11)
Tc1—C3	2.027 (3)	O6—Cl1	1.422 (6)
Tc1—C2^i	2.029 (3)	O6—Cl1^iv	2.144 (6)
Tc1—C2	2.029 (3)	Cl1—Cl1^iv	0.728 (3)
C1—O3	1.113 (4)	Cl1—O5^iv	1.286 (8)
C2—O1	1.114 (4)	Cl1—O4^v	1.393 (3)
C3—O2	1.113 (4)	Cl1—O4^iii	1.444 (3)
O4—Cl1^ii	1.393 (3)	Cl1—O6^iv	2.144 (6)
O4—Cl1^iii	1.444 (3)
C1^i—Tc1—C1	180.0 (2)	O1—C2—Tc1	179.6 (3)
C1^i—Tc1—C3^i	91.27 (14)	O2—C3—Tc1	177.0 (3)
C1—Tc1—C3^i	88.73 (14)	O5^iv—Cl1—O4^v	124.7 (11)
C1^i—Tc1—C3	88.73 (14)	O4^v—Cl1—O5	107.0 (10)
C1—Tc1—C3	91.27 (14)	O5^iv—Cl1—O6	86.5 (11)
C3^i—Tc1—C3	180.0 (3)	O4^v—Cl1—O6	108.6 (3)
C1^i—Tc1—C2^i	89.61 (12)	O5—Cl1—O6	108.9 (9)
C1—Tc1—C2^i	90.39 (12)	O5^iv—Cl1—O4^iii	112.3 (14)
C3^i—Tc1—C2^i	88.56 (12)	O4^v—Cl1—O4^iii	112.1 (3)
C3—Tc1—C2^i	91.44 (12)	O5—Cl1—O4^iii	111.5 (13)
C1^i—Tc1—C2	90.39 (12)	O6—Cl1—O4^iii	108.6 (3)
C1—Tc1—C2	89.61 (12)	O5^iv—Cl1—O6^iv	80.9 (11)
C3^i—Tc1—C2	91.44 (12)	O4^v—Cl1—O6^iv	79.2 (2)
C3—Tc1—C2	88.56 (12)	O5—Cl1—O6^iv	58.6 (10)
C2^i—Tc1—C2	180.00 (17)	O6—Cl1—O6^iv	167.4 (6)
O3—C1—Tc1	177.6 (3)	O4^iii—Cl1—O6^iv	76.4 (2)

Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) x−1/2, −y−1/2, z−1/2; (iii) −x+1/2, −y−1/2, −z; (iv) −x+1, y, −z+1/2; (v) x+1/2, −y−1/2, z+1/2.