metal-organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
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ISSN: 2056-9890
Volume 68| Part 9| September 2012| Pages m1167-m1168

Bis[μ-N-(tert-butyl­di­methyl­silyl)-N-(pyridin-2-ylmeth­yl)amido]­bis­­[methyl­cobalt(II)]

aInstitut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität, Jena, Humboldt-Strasse 8, 07743 Jena, Germany
*Correspondence e-mail: m.we@uni-jena.de

(Received 6 July 2012; accepted 16 July 2012; online 11 August 2012)

The green title complex, [Co2(CH3)2(C12H21N2Si)2], was obtained from bis­{[μ-N-tert-butyl­dimethyl­silyl-N-(pyridin-2-ylmeth­yl)amido]­chloridocobalt(II)} and methyl­lithium in diethyl ether at 195 K via a metathesis reaction. The dimeric cobalt(II) complex exhibits a crystallographic center of inversion in the middle of the Co2N2 ring (average Co—N = 2.050 Å). The CoII atom shows a distorted tetra­hedral coordination sphere. The exocyclic Co—N bond length to the pyridyl group shows a similar value of 2.045 (4) Å. The exocyclic methyl group has a rather long Co—C bond length of 2.019 (5) Å.

Related literature

The metathetical conversion of a cobalt chloride functionality into a methyl cobalt fragment via the reaction with methyllithium was reported earlier for tetra-coordinate cobalt(II) complexes bound to three additional aza-bases, see: Au-Yeung et al. (2007[Au-Yeung, H. Y., Lam, C. H., Lam, C., Wong, W. & Lee, H. K. (2007). Inorg. Chem. 46, 7695-7697.]); Bowman et al. (2010[Bowman, A. C., Milsmann, C., Bill, E., Lobkovsky, E., Weyhermüller, T., Wieghardt, K. & Chirik, P. J. (2010). Inorg. Chem. 49, 6110-6123.]); Humphries et al. (2005[Humphries, M. J., Tellmann, K. P., Gibson, V. C., White, A. J. P. & Williams, D. J. (2005). Organometallics, 24, 2039-2050.]); Kleigrewe et al. (2005[Kleigrewe, N., Steffen, W., Blömker, T., Kehr, G., Fröhlich, R., Wibbeling, B., Erker, G., Wasilke, J.-C., Wu, G. & Bazan, G. C. (2005). J. Am. Chem. Soc. 127, 13955-13968.]), Wallenhorst et al. (2008[Wallenhorst, C., Kehr, G., Luftmann, H., Fröhlich, R. & Erker, G. (2008). Organometallics, 27, 6547-6556.]). The synthesis of dialkyl cobalt complexes succeeds starting from hexa-coordinate [(L)4CoCl2] with L being a pyridyl base, see: Milani et al. (2003[Milani, B., Stabon, E., Zangrando, E., Mestroni, G., Sommazzi, A. & Zannoni, C. (2003). Inorg. Chim. Acta, 349, 209-216.]); Zhu et al. (2010[Zhu, D., Janssen, F. F. B. J. & Budzelaar, P. H. M. (2010). Organometallics, 29, 1897-1908.]). The coordination number of the final cobalt(II) complexes depends on intra­molecular steric strain yielding hexa-coordinate [(bpy)2CoMe2] (bpy = 2,2′-bipyridine) and tetra-coordinate [(py)2CoR2] (R = CH2C(Me2)Ph). The formation of para-tolyl­cobalt complexes was reported by Zhu & Budzelaar (2010[Zhu, D. & Budzelaar, P. H. M. (2010). Organometallics, 29, 5759-5761.]) who proposed a radical mechanism.

[Scheme 1]

Experimental

Crystal data
  • [Co2(CH3)2(C12H21N2Si)2]

  • Mr = 590.72

  • Triclinic, [P \overline 1]

  • a = 8.4751 (8) Å

  • b = 9.8055 (12) Å

  • c = 10.6130 (6) Å

  • α = 72.837 (6)°

  • β = 83.450 (6)°

  • γ = 69.216 (6)°

  • V = 787.81 (13) Å3

  • Z = 1

  • Mo Kα radiation

  • μ = 1.15 mm−1

  • T = 183 K

  • 0.06 × 0.06 × 0.04 mm

Data collection
  • Nonius KappaCCD diffractometer

  • 5417 measured reflections

  • 3551 independent reflections

  • 1685 reflections with I > 2σ(I)

  • Rint = 0.074

Refinement
  • R[F2 > 2σ(F2)] = 0.061

  • wR(F2) = 0.129

  • S = 0.92

  • 3551 reflections

  • 160 parameters

  • H-atom parameters constrained

  • Δρmax = 0.39 e Å−3

  • Δρmin = −0.39 e Å−3

Data collection: COLLECT (Nonius, 1998[Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.]); cell refinement: DENZO (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.]); data reduction: DENZO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL/PC (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXL97.

Supporting information


Comment top

Au-Yeung et al. (2007) performed a metathetical ligand substitution reaction at (tmeda)cobalt(II) 2,6-dimethylphenyl-N-trimethylsilylamide chloride (tmeda = tetramethylethylenediamine) with methyllithium in toluene. Whereas in this complex the cobalt(II) adopts a distorted tetrahedral coordination sphere, severe distortions were observed using tridentate aza-Lewis bases (Bowman et al., 2010; Humphries et al., 2005; Kleigrewe et al., 2005; Wallenhorst et al., 2008). Treatment of tetrakis(pyridine)cobalt(II) dichloride with trimethylsilylmethyllithium or 2-methyl-2-phenylpropyllithium in n-pentane yielded [(py)2CoR2] (R = CH2SiMe3)2, CH2C(Me2)Ph), respectively, with tetra-coordinate cobalt centers (Zhu et al., 2010). Less bulky methyl groups allowed the formation of [(bpy)2CoMe2] with a hexa-coordinate cobalt atom in a slightly distorted octahedral environment (Milani et al., 2003). Contrary to these procedures, a radical mechanism was discussed by Zhu & Budzelaar (2010) for the formation of para-tolyl-cobalt complexes. Whereas all of these cobalt(II) complexes represent mononuclear derivatives, the reaction of bis[N-(pyidin-2-ylmethyl)-N-(tert-butyldimethylsilyl)amido cobalt(II) chloride] with methyllithium in tetrahydrofuran (THF) yielded the centrosymmetric dinuclear title compound 1 with a central planar Co2N2 ring.

Related literature top

The metathetical conversion of a cobalt chloride functionality into a methyl cobalt fragment via the reaction with LiR was reported earlier for tetra-coordinate cobalt(II) complexes bound to three additional aza-bases, see: Au-Yeung et al. (2007); Bowman et al. (2010); Humphries et al. (2005); Kleigrewe et al. (2005), Wallenhorst et al. (2008). The synthesis of dialkyl cobalt complexes succeeds starting from hexa-coordinate [(L)4CoCl2] with L being a pyridyl base, see: Milani et al. (2003); Zhu et al. (2010). The coordination number of the final cobalt(II) complexes depends on intramolecular steric strain yielding hexa-coordinate [(bpy)2CoMe2] (bpy = 2,2'-bipyridine) and tetra-coordinate [(py)2CoR2] (R = CH2C(Me2)Ph). The formation of para-tolylcobalt complexes was reported by Zhu & Budzelaar (2010) who proposed a radical mechanism.

Experimental top

Bis{chlorido-[N-(pyidin-2-ylmethyl)-N-(tert-butyldimethylsilyl)amido]cobalt(II)} (0.84 g, 1.32 mmol) was dissolved in 15 ml of THF and this solution cooled to -78 °C. Then 1.7 ml (2,72 mmol) of a 1,6M methyllithium solution in diethyl ether was added dropwise. A brown reaction solution formed which was warmed to ambient temperature and stirred for an additional hour. Thereafter all volatile materials were removed and the residue dried in vacuo. This residue was extracted with 15 ml of n-hexane. The volume of this solution was reduced to third of the original volume and cooled to -20 °C. Within several hours green rod-like crystals of 1 precipitated. Yield: 0.21 g (0.36 mmol, 27%).

Refinement top

All hydrogen atoms were calculated to idealized positions with C–H distances of 0.98 (methyl), 0.99 (methylene) and 0.95 (phenyl) Å, and were refined with 1.2 times (1.5 for all methyl groups) the isotropic displacement parameter of the corresponding carbon atom. All methyl groups were allowed to rotate but not to tip.

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997); data reduction: DENZO (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL/PC (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Molecular structure and numbering scheme of the title compound 1; Displacement ellipsoids are at the 40% probability level. H atoms are neglected for clarity reasons. Symmetry-related atoms are marked with the letter i [symmetry code: (i) -x + 1, -y + 1, -z + 1].
[Figure 2] Fig. 2. Packing of the molecules by short ring-interactions (distance between the centroids of the aromatic rings 3.689 (3) Å).
Bis[µ-N-(tert-butyldimethylsilyl)-N-(pyridin-2- ylmethyl)amido]bis[methylcobalt(II)] top
Crystal data top
[Co2(CH3)2(C12H21N2Si)2]Z = 1
Mr = 590.72F(000) = 314
Triclinic, P1Dx = 1.245 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 8.4751 (8) ÅCell parameters from 5417 reflections
b = 9.8055 (12) Åθ = 3.3–27.5°
c = 10.6130 (6) ŵ = 1.15 mm1
α = 72.837 (6)°T = 183 K
β = 83.450 (6)°Prism, green
γ = 69.216 (6)°0.06 × 0.06 × 0.04 mm
V = 787.81 (13) Å3
Data collection top
Nonius KappaCCD
diffractometer
1685 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.074
Graphite monochromatorθmax = 27.5°, θmin = 3.3°
phi– + ω–scanh = 109
5417 measured reflectionsk = 1012
3551 independent reflectionsl = 1313
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.061Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.129H-atom parameters constrained
S = 0.92 w = 1/[σ2(Fo2) + (0.0369P)2]
where P = (Fo2 + 2Fc2)/3
3551 reflections(Δ/σ)max < 0.001
160 parametersΔρmax = 0.39 e Å3
0 restraintsΔρmin = 0.39 e Å3
Crystal data top
[Co2(CH3)2(C12H21N2Si)2]γ = 69.216 (6)°
Mr = 590.72V = 787.81 (13) Å3
Triclinic, P1Z = 1
a = 8.4751 (8) ÅMo Kα radiation
b = 9.8055 (12) ŵ = 1.15 mm1
c = 10.6130 (6) ÅT = 183 K
α = 72.837 (6)°0.06 × 0.06 × 0.04 mm
β = 83.450 (6)°
Data collection top
Nonius KappaCCD
diffractometer
1685 reflections with I > 2σ(I)
5417 measured reflectionsRint = 0.074
3551 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0610 restraints
wR(F2) = 0.129H-atom parameters constrained
S = 0.92Δρmax = 0.39 e Å3
3551 reflectionsΔρmin = 0.39 e Å3
160 parameters
Special details top

Experimental. IR (in Nujol between KBr windows, cm-1): = 1715 w, 1583 m, 1273 m, 1244 s, 1146 m, 1080 m, 1036 m, 1008 m, 889 m, 828 s, 770 m, 736 m. MS (DEI, rel. intensity in brackets): m/z = 501 ([M - CoMe2]+, 11%), 165 ([Pyr-CH2-NHSiMe2]+, 100%). Elemental analysis (C26H48Co2N4Si2, 590,72): calcd.: C 52.86, H 8.19, N 9.48; found: C 49.47, H 7.70, N 9.03 (the rather large deviations are caused by extreme sensitivity of the complex towards moisture and air; the low carbon value is a consequence of carbide and carbonate formation despite the fact that V2O5 was added prior to combustion).

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
Co10.50875 (8)0.62393 (8)0.52394 (5)0.0360 (2)
Si10.36965 (16)0.43232 (17)0.77488 (11)0.0373 (4)
N10.2891 (5)0.7874 (4)0.4452 (3)0.0342 (10)
N20.3562 (4)0.4948 (4)0.6037 (3)0.0306 (9)
C10.2668 (7)0.9328 (6)0.3756 (4)0.0466 (14)
H1A0.35990.96810.36360.056*
C20.1139 (7)1.0311 (6)0.3217 (4)0.0524 (15)
H2A0.10171.13250.27320.063*
C30.0218 (7)0.9803 (7)0.3391 (5)0.0570 (16)
H3A0.12751.04520.30030.068*
C40.0012 (6)0.8329 (6)0.4142 (4)0.0429 (13)
H4A0.09380.79670.42940.052*
C50.1560 (6)0.7389 (6)0.4668 (4)0.0349 (12)
C60.1808 (5)0.5827 (6)0.5525 (4)0.0387 (12)
H6A0.15010.52560.50200.046*
H6B0.10200.58920.62860.046*
C70.2682 (6)0.5989 (6)0.8446 (4)0.0529 (15)
H7A0.32430.67420.80800.079*
H7B0.27880.56480.94080.079*
H7C0.14850.64450.82130.079*
C80.5975 (6)0.3468 (6)0.8222 (4)0.0504 (15)
H8A0.65710.41650.77460.076*
H8B0.64790.25040.79930.076*
H8C0.60670.32880.91740.076*
C90.2621 (6)0.2877 (6)0.8564 (4)0.0430 (13)
C100.0704 (6)0.3488 (6)0.8314 (5)0.0594 (16)
H10A0.02080.27190.88080.089*
H10B0.05050.37220.73700.089*
H10C0.01800.44110.86060.089*
C110.3389 (6)0.1452 (6)0.8085 (4)0.0502 (14)
H11A0.27900.07390.84990.075*
H11B0.45840.09760.83240.075*
H11C0.32880.17280.71250.075*
C120.2873 (7)0.2393 (7)1.0077 (4)0.0700 (19)
H12A0.24150.15751.04910.105*
H12B0.22840.32631.04300.105*
H12C0.40800.20341.02670.105*
C130.6200 (6)0.7259 (7)0.6082 (4)0.0580 (16)
H13A0.62690.81890.54420.087*
H13B0.73390.65710.63630.087*
H13C0.55320.75100.68500.087*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Co10.0333 (4)0.0450 (5)0.0363 (4)0.0195 (3)0.0038 (3)0.0147 (3)
Si10.0355 (8)0.0459 (10)0.0285 (7)0.0122 (8)0.0012 (5)0.0098 (6)
N10.039 (2)0.033 (3)0.033 (2)0.015 (2)0.0103 (16)0.0130 (19)
N20.026 (2)0.036 (3)0.0285 (17)0.009 (2)0.0019 (15)0.0068 (16)
C10.051 (4)0.038 (4)0.050 (3)0.017 (3)0.020 (3)0.015 (3)
C20.059 (4)0.037 (4)0.048 (3)0.010 (3)0.011 (3)0.004 (3)
C30.051 (4)0.050 (4)0.054 (3)0.000 (3)0.005 (3)0.010 (3)
C40.032 (3)0.045 (4)0.046 (3)0.009 (3)0.001 (2)0.010 (3)
C50.037 (3)0.041 (3)0.024 (2)0.012 (3)0.0019 (19)0.008 (2)
C60.038 (3)0.044 (4)0.037 (2)0.022 (3)0.003 (2)0.007 (2)
C70.061 (4)0.057 (4)0.045 (3)0.018 (3)0.003 (2)0.024 (3)
C80.045 (3)0.070 (4)0.038 (3)0.014 (3)0.007 (2)0.020 (3)
C90.044 (3)0.042 (4)0.029 (2)0.005 (3)0.005 (2)0.003 (2)
C100.050 (4)0.054 (4)0.068 (3)0.022 (3)0.016 (3)0.009 (3)
C110.048 (3)0.042 (4)0.056 (3)0.018 (3)0.010 (2)0.007 (3)
C120.084 (4)0.064 (5)0.040 (3)0.019 (4)0.001 (3)0.009 (3)
C130.055 (4)0.089 (5)0.055 (3)0.047 (4)0.013 (3)0.034 (3)
Geometric parameters (Å, º) top
Co1—C132.019 (5)C6—H6B0.9900
Co1—N2i2.032 (3)C7—H7A0.9800
Co1—N12.045 (4)C7—H7B0.9800
Co1—N22.067 (4)C7—H7C0.9800
Co1—Co1i2.6812 (14)C8—H8A0.9800
Si1—N21.741 (3)C8—H8B0.9800
Si1—C81.873 (4)C8—H8C0.9800
Si1—C71.877 (5)C9—C111.528 (7)
Si1—C91.898 (5)C9—C101.544 (6)
N1—C51.345 (5)C9—C121.551 (6)
N1—C11.354 (6)C10—H10A0.9800
N2—C61.499 (5)C10—H10B0.9800
N2—Co1i2.032 (3)C10—H10C0.9800
C1—C21.376 (6)C11—H11A0.9800
C1—H1A0.9500C11—H11B0.9800
C2—C31.381 (7)C11—H11C0.9800
C2—H2A0.9500C12—H12A0.9800
C3—C41.388 (7)C12—H12B0.9800
C3—H3A0.9500C12—H12C0.9800
C4—C51.390 (6)C13—H13A0.9800
C4—H4A0.9500C13—H13B0.9800
C5—C61.487 (6)C13—H13C0.9800
C6—H6A0.9900
C13—Co1—N2i119.40 (17)N2—C6—H6B108.5
C13—Co1—N1105.8 (2)H6A—C6—H6B107.5
N2i—Co1—N1112.97 (13)Si1—C7—H7A109.5
C13—Co1—N2130.97 (16)Si1—C7—H7B109.5
N2i—Co1—N298.30 (12)H7A—C7—H7B109.5
N1—Co1—N284.19 (15)Si1—C7—H7C109.5
C13—Co1—Co1i151.34 (17)H7A—C7—H7C109.5
N2i—Co1—Co1i49.71 (10)H7B—C7—H7C109.5
N1—Co1—Co1i102.57 (11)Si1—C8—H8A109.5
N2—Co1—Co1i48.59 (10)Si1—C8—H8B109.5
N2—Si1—C8108.95 (18)H8A—C8—H8B109.5
N2—Si1—C7109.2 (2)Si1—C8—H8C109.5
C8—Si1—C7108.4 (2)H8A—C8—H8C109.5
N2—Si1—C9114.74 (19)H8B—C8—H8C109.5
C8—Si1—C9108.4 (2)C11—C9—C10107.8 (4)
C7—Si1—C9107.0 (2)C11—C9—C12107.5 (4)
C5—N1—C1119.0 (4)C10—C9—C12107.5 (4)
C5—N1—Co1113.7 (3)C11—C9—Si1111.1 (3)
C1—N1—Co1127.3 (3)C10—C9—Si1113.3 (3)
C6—N2—Si1114.5 (2)C12—C9—Si1109.4 (3)
C6—N2—Co1i109.3 (2)C9—C10—H10A109.5
Si1—N2—Co1i125.9 (2)C9—C10—H10B109.5
C6—N2—Co1108.8 (3)H10A—C10—H10B109.5
Si1—N2—Co1111.27 (17)C9—C10—H10C109.5
Co1i—N2—Co181.70 (12)H10A—C10—H10C109.5
N1—C1—C2122.1 (5)H10B—C10—H10C109.5
N1—C1—H1A118.9C9—C11—H11A109.5
C2—C1—H1A118.9C9—C11—H11B109.5
C1—C2—C3119.1 (5)H11A—C11—H11B109.5
C1—C2—H2A120.4C9—C11—H11C109.5
C3—C2—H2A120.4H11A—C11—H11C109.5
C2—C3—C4119.0 (5)H11B—C11—H11C109.5
C2—C3—H3A120.5C9—C12—H12A109.5
C4—C3—H3A120.5C9—C12—H12B109.5
C3—C4—C5119.4 (5)H12A—C12—H12B109.5
C3—C4—H4A120.3C9—C12—H12C109.5
C5—C4—H4A120.3H12A—C12—H12C109.5
N1—C5—C4121.3 (4)H12B—C12—H12C109.5
N1—C5—C6117.8 (4)Co1—C13—H13A109.5
C4—C5—C6120.8 (4)Co1—C13—H13B109.5
C5—C6—N2115.1 (4)H13A—C13—H13B109.5
C5—C6—H6A108.5Co1—C13—H13C109.5
N2—C6—H6A108.5H13A—C13—H13C109.5
C5—C6—H6B108.5H13B—C13—H13C109.5
Symmetry code: (i) x+1, y+1, z+1.

Experimental details

Crystal data
Chemical formula[Co2(CH3)2(C12H21N2Si)2]
Mr590.72
Crystal system, space groupTriclinic, P1
Temperature (K)183
a, b, c (Å)8.4751 (8), 9.8055 (12), 10.6130 (6)
α, β, γ (°)72.837 (6), 83.450 (6), 69.216 (6)
V3)787.81 (13)
Z1
Radiation typeMo Kα
µ (mm1)1.15
Crystal size (mm)0.06 × 0.06 × 0.04
Data collection
DiffractometerNonius KappaCCD
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
5417, 3551, 1685
Rint0.074
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.061, 0.129, 0.92
No. of reflections3551
No. of parameters160
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.39, 0.39

Computer programs: COLLECT (Nonius, 1998), DENZO (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL/PC (Sheldrick, 2008).

 

Acknowledgements

We thank the Deutsche Forschungsgemeinschaft (DFG, Bonn–Bad Godesberg, Germany) for generous financial support. We also acknowledge funding from the Fonds der Chemischen Industrie (Frankfurt/Main, Germany).

References

First citationAu-Yeung, H. Y., Lam, C. H., Lam, C., Wong, W. & Lee, H. K. (2007). Inorg. Chem. 46, 7695–7697.  Web of Science PubMed CAS
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Volume 68| Part 9| September 2012| Pages m1167-m1168
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