Tris{2-[(2,6-dimethyl­phen­yl)amino]­eth­yl}amine

Moroz, Y.S.; Takase, M.K.; Müller, P.; Rybak-Akimova, E.V.

doi:10.1107/S1600536811049397

organic compounds

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Volume 67| Part 12| December 2011| Page o3421

https://doi.org/10.1107/S1600536811049397

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Tris{2-[(2,6-dimethylphenyl)amino]ethyl}amine

Yurii S. Moroz,^a Michael K. Takase,^b Peter Müller ^b and Elena V. Rybak-Akimova ^a ^*

^aDepartment of Chemistry, Tufts University, 62 Talbot Avenue, Medford, MA 02155, USA, and ^bDepartment of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
^*Correspondence e-mail: elena.rybak-akimova@tufts.edu

(Received 16 November 2011; accepted 18 November 2011; online 25 November 2011)

The title compound, C₃₀H₄₂N₄, is an arylated tris(aminoethyl)amine derivative which was obtained by reducing the corresponding tris-amide with AlH₃. The asymmetric unit consists of one third of a C_3v-symmetric molecule with the tertiary N atom lying on a crystallographic threefold axis.

Related literature

For the structural parameters of arylated derivatives of tris(aminoethyl)amine, see: Almesåker et al. (2009 ); Amoroso et al. (2009 ). For the synthesis and the structural parameters of metal complexes based on arylated derivatives of tris(aminoethyl)amine, see: Morton et al. (2000 ); Yandulov & Schrock (2005 ); Smythe et al. (2006 ); Reithofer et al. (2010 ); Almesåker et al. (2010 ).

Experimental

Crystal data

C₃₀H₄₂N₄
M_r = 458.68
Trigonal, $[R \overline 3]$
a = 14.2880 (7) Å
c = 22.3811 (11) Å
V = 3956.9 (5) Å³
Z = 6
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 100 K
0.1 × 0.1 × 0.1 mm

Data collection

Bruker SMART APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2009 ) T_min = 0.680, T_max = 0.746
20390 measured reflections
2695 independent reflections
2330 reflections with I > 2σ(I)
R_int = 0.031

Refinement

R[F² > 2σ(F²)] = 0.041
wR(F²) = 0.113
S = 1.06
2695 reflections
109 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.42 e Å⁻³
Δρ_min = −0.18 e Å⁻³

Data collection: APEX2 (Bruker, 2009 ); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536811049397/zl2430sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536811049397/zl2430Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S1600536811049397/zl2430Isup3.cml

checkCIF report

Comment top

Tris(aminoethyl)amine derivatives have attracted attention of chemists due to their ability to adopt a trigonal pyramidal geometry which is favourable for coordination of different metal ions in a trigonal bipyramidal environment, with one open coordination site for a small exchangeable ligand (Morton et al., 2000; Yandulov et al., 2005; Smythe et al., 2006; Reithofer et al., 2010; Almesåker et al., 2010). In this report, we disscuss the molecular structure of an arylated tris(aminoethyl)amine derivative which appears to be a promising ligand for obtaining high valent iron compounds.

The title compound (1) crystallizes in the trigonal space group R3 and consists of neutral molecules (Figure 1); inter-molecular interactions include a number of van der Waals and C–H···π contacts. There are two types of the C—H···π contacts that originate from hydrogen atoms of the methyl groups pointing towards the opposite sides of the same aromatic ring; no aryl H atoms are involved. The first type of non-covalent interactions has a C10 atom acting as a donor (the C—H···π separation is 3.530 (1) A) and results in the formation of pseudo-dimer aggregates (Figure 2) which form a three-dimensional, well defined symmetric cavity via the second type of C—H···π contacts and van der Waals contacts. The second type of C–H···π contacts includes C9 as a donor (the C–H···π separation is 3.641 (1) Å).

The secondary amino group is located in a cis-position to the tertiary N atom (N1—C1—C2—N2 torsion angle is 54.0 (1)°). The C—C, C—N bond lengths are comparable to the previously reported structures of arylated derivatives of tris(aminoethyl)amine (Almesåker et al., 2009; Amoroso et al., 2009).

Related literature top

For the structural parameters of arylated derivatives of tris(aminoethyl)amine, see: Almesåker et al. (2009); Amoroso et al. (2009). For the synthesis and the structural parameters of metal complexes based on arylated derivatives of tris(aminoethyl)amine, see: Morton et al. (2000); Yandulov & Schrock (2005); Smythe et al. (2006); Reithofer et al. (2010); Almesåker et al. (2010).

Experimental top

The title compound, (1), was obtained in three steps. Nitrilotriacetoanilide, (ArNC(O)CH₂)₃N, where Ar = Me₂C₆H₃, was synthesized via the reaction of nitrilotriacetic acid chloride and 2,6-dimethylaniline. The acid chloride was prepared in situ: Oxalyl chloride (10.6 ml) was added dropwise to a cooled (278 K, 5 °C) mixture of nitrilotriacetic acid (5 g, 0.03 mol, in 100 ml of DCM) with one drop of DMF as a catalyst. The mixture was stirred for 48 h at room temperature, and then the DCM and extra oxalyl chloride were removed by vacuum distillation. The crude acid chloride was dissolved in 50 ml of DCM and added dropwise to a 100 ml of DCM solution of 2,6-dimethylaniline (9.8 ml, 0.08 mol) and N-ethyldiisopropylamine (18.5 ml, 0.11 mol) at 263 K (–10 °C). After the addition was complete, the reaction mixture was allowed to warm up and stirred for 24 h at ambient temperature. The reaction mixture was washed with 1 N HCl (25 ml), and then with saturated NaHCO₃ (25 ml). The organic layer was dried (Na₂SO₄) and concentrated under reduced pressure. The solid was washed with water/methanol, 1/1 (v/v), filtered, and dried in an oven at 373 K (100 °C) for 2 days. Yield: 3.07 g (23%). ¹H NMR (300 MHz, dmso-d₆): δ 2.16 (s, 18, Me), 3.70 (s, 6, CH₂), 7.08 (m, 9, H_p, 2H_m), 9.63 (s, 3, NH). ¹³C NMR (75 MHz, dmso-d₆): δ 18.21, 57.99, 126.6, 127.74, 134.86, 135.21, 168.82.

N¹,N²,N³-Tris((2,6-dimethylphenyl)amino)ethyl)amine: To 200 ml of dry THF, 7.20 g (0.2 mol) of LiAlH₄ was added slowly in portions. Then the reaction mixture was cooled in an ice bath and 26 ml (0.2 mol) of chlorotrimethylsilane was added dropwise, followed by an addition of 3.07 g (0.006 mol) of nitrilotriacetoanilide. The reaction mixture was refluxed for 14 h (the reaction was controlled by NMR) and then cooled down to room temperature. Then 21 ml of water in 40 ml of THF was carefully added to the reaction mixture, followed by the addition of NaOH (50%, 21 ml). The reaction mixture was filtered, the precipitate was washed with THF (100 ml) and the filtrate was evaporated under reduced pressure. The solid was extracted with DCM (100 ml); the DCM solution was dried (Na₂SO₄) and concentrated. The crude product was washed with cold diethyl ether (100 ml), filtered, and dried under reduced pressure. Yield: 1.5 g (54%). Colourless crystals, which were suitable for X-ray analysis, were grown in an NMR tube from the dmso-d₆ solution. ¹H NMR (300 MHz, dmso-d₆): δ 2.18 (s, 18, Me), 2.64 (t, J = 6.3 Hz, 6, CH₂), 2.99 (td, J = 6.3, 6 Hz, 6, CH₂), 3.83 (t, J = 6 Hz, 3, NH), 6.69 (t, J = 7.2 Hz, 3, H_p), 6.90 (d, J = 7.2 Hz, 6, H_m). ¹³C NMR (75 MHz, dmso-d₆): δ 18.47, 45.54, 54.51, 120.8, 128.51, 146.38.

Structure description top

For the structural parameters of arylated derivatives of tris(aminoethyl)amine, see: Almesåker et al. (2009); Amoroso et al. (2009). For the synthesis and the structural parameters of metal complexes based on arylated derivatives of tris(aminoethyl)amine, see: Morton et al. (2000); Yandulov & Schrock (2005); Smythe et al. (2006); Reithofer et al. (2010); Almesåker et al. (2010).

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top

	Fig. 1. A view of the title compound, with displacement ellipsoids shown at the 50% probability level. Symmetry transformations used to generate equivalent atoms: (i) -y+1, x-y, z; (ii) -x+y+1, -x+1, z.
	Fig. 2. A fragment of the packing diagram of the title compound, with displacement ellipsoids shown at the 50% probability level (H atoms, except H atoms attached to C10 atom, are omitted for clarity). Symmetry transformations used to generate equivalent atoms: (i) -y+1, x-y, z; (ii) -x+y+1, -x+1, z; (iii) 1/3+x-y, -1/3+x, 2/3-z; (iv) 1/3+y, 2/3-x+y, 2/3-z; (v) 1/3-x, 2/3-y, 2/3-z.

Tris{2-[(2,6-dimethylphenyl)amino]ethyl}amine top

Crystal data top

C₃₀H₄₂N₄	D_x = 1.155 Mg m⁻³
M_r = 458.68	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3	Cell parameters from 9944 reflections
Hall symbol: -R 3	θ = 2.5–30.6°
a = 14.2880 (7) Å	µ = 0.07 mm⁻¹
c = 22.3811 (11) Å	T = 100 K
V = 3956.9 (5) Å³	Block, colourless
Z = 6	0.1 × 0.1 × 0.1 mm
F(000) = 1500

Data collection top

Bruker Smart APEXII CCD diffractometer	2695 independent reflections
Radiation source: ImuS micro-focus sealed tube	2330 reflections with I > 2σ(I)
Icoatech ImuS multilayer optics monochromator	R_int = 0.031
Detector resolution: 8.3 pixels mm^-1	θ_max = 30.6°, θ_min = 1.9°
φ and ω scans	h = −20→20
Absorption correction: multi-scan (SADABS; Sheldrick, 2009)	k = −20→20
T_min = 0.680, T_max = 0.746	l = −31→31
20390 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.041	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.113	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ²(F_o²) + (0.0529P)² + 4.1067P] where P = (F_o² + 2F_c²)/3
2695 reflections	(Δ/σ)_max < 0.001
109 parameters	Δρ_max = 0.42 e Å⁻³
0 restraints	Δρ_min = −0.18 e Å⁻³

Crystal data top

C₃₀H₄₂N₄	Z = 6
M_r = 458.68	Mo Kα radiation
Trigonal, R3	µ = 0.07 mm⁻¹
a = 14.2880 (7) Å	T = 100 K
c = 22.3811 (11) Å	0.1 × 0.1 × 0.1 mm
V = 3956.9 (5) Å³

Data collection top

Bruker Smart APEXII CCD diffractometer	2695 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2009)	2330 reflections with I > 2σ(I)
T_min = 0.680, T_max = 0.746	R_int = 0.031
20390 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.041	0 restraints
wR(F²) = 0.113	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	Δρ_max = 0.42 e Å⁻³
2695 reflections	Δρ_min = −0.18 e Å⁻³
109 parameters

Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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

	x	y	z	U_iso*/U_eq
C1	0.58018 (7)	0.22760 (7)	0.11134 (4)	0.01668 (18)
H1A	0.5860	0.2233	0.0675	0.020*
H1B	0.5095	0.2218	0.1200	0.020*
C2	0.58289 (8)	0.13268 (7)	0.13995 (4)	0.01696 (18)
H2A	0.5189	0.0642	0.1271	0.020*
H2B	0.6485	0.1316	0.1268	0.020*
C3	0.58132 (7)	0.05566 (7)	0.23806 (4)	0.01446 (17)
C4	0.48468 (7)	−0.04409 (7)	0.24161 (4)	0.01604 (18)
C5	0.48377 (8)	−0.12750 (8)	0.27456 (4)	0.01872 (19)
H5	0.4192	−0.1956	0.2766	0.022*
C6	0.57519 (8)	−0.11311 (8)	0.30435 (4)	0.01925 (19)
H6	0.5732	−0.1708	0.3264	0.023*
C7	0.66954 (8)	−0.01359 (8)	0.30156 (4)	0.01794 (18)
H7	0.7318	−0.0032	0.3225	0.022*
C8	0.67430 (7)	0.07137 (7)	0.26845 (4)	0.01593 (18)
C9	0.38314 (8)	−0.06114 (8)	0.21179 (5)	0.0221 (2)
H9A	0.3838	−0.0794	0.1696	0.033*
H9B	0.3791	0.0052	0.2146	0.033*
H9C	0.3202	−0.1203	0.2316	0.033*
C10	0.77793 (8)	0.17807 (8)	0.26578 (5)	0.0238 (2)
H10A	0.8351	0.1721	0.2866	0.036*
H10B	0.7675	0.2338	0.2850	0.036*
H10C	0.7988	0.1979	0.2240	0.036*
N1	0.6667	0.3333	0.13202 (6)	0.0142 (2)
N2	0.58312 (7)	0.14184 (6)	0.20523 (4)	0.01647 (17)
H2N	0.6392 (12)	0.2043 (12)	0.2164 (6)	0.024 (3)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0167 (4)	0.0151 (4)	0.0166 (4)	0.0067 (3)	−0.0036 (3)	−0.0003 (3)
C2	0.0202 (4)	0.0147 (4)	0.0158 (4)	0.0086 (3)	−0.0020 (3)	−0.0008 (3)
C3	0.0160 (4)	0.0149 (4)	0.0142 (4)	0.0090 (3)	−0.0006 (3)	−0.0009 (3)
C4	0.0154 (4)	0.0168 (4)	0.0159 (4)	0.0081 (3)	−0.0001 (3)	−0.0016 (3)
C5	0.0195 (4)	0.0153 (4)	0.0201 (4)	0.0077 (3)	0.0034 (3)	0.0007 (3)
C6	0.0240 (4)	0.0184 (4)	0.0196 (4)	0.0137 (4)	0.0037 (3)	0.0036 (3)
C7	0.0191 (4)	0.0216 (4)	0.0173 (4)	0.0133 (4)	−0.0003 (3)	0.0011 (3)
C8	0.0155 (4)	0.0164 (4)	0.0160 (4)	0.0081 (3)	−0.0008 (3)	−0.0007 (3)
C9	0.0149 (4)	0.0237 (5)	0.0238 (5)	0.0068 (4)	−0.0031 (3)	−0.0002 (4)
C10	0.0176 (4)	0.0201 (4)	0.0286 (5)	0.0055 (4)	−0.0063 (4)	0.0024 (4)
N1	0.0130 (3)	0.0130 (3)	0.0167 (6)	0.00651 (17)	0.000	0.000
N2	0.0204 (4)	0.0139 (3)	0.0158 (4)	0.0091 (3)	−0.0030 (3)	−0.0011 (3)

Geometric parameters (Å, º) top

C1—N1	1.4686 (10)	C6—C7	1.3879 (14)
C1—C2	1.5178 (12)	C6—H6	0.9500
C1—H1A	0.9900	C7—C8	1.3946 (12)
C1—H1B	0.9900	C7—H7	0.9500
C2—N2	1.4667 (12)	C8—C10	1.5043 (13)
C2—H2A	0.9900	C9—H9A	0.9800
C2—H2B	0.9900	C9—H9B	0.9800
C3—C4	1.4059 (12)	C9—H9C	0.9800
C3—C8	1.4069 (12)	C10—H10A	0.9800
C3—N2	1.4231 (11)	C10—H10B	0.9800
C4—C5	1.3961 (13)	C10—H10C	0.9800
C4—C9	1.5020 (13)	N1—C1ⁱ	1.4686 (10)
C5—C6	1.3872 (14)	N1—C1ⁱⁱ	1.4686 (10)
C5—H5	0.9500	N2—H2N	0.886 (15)

N1—C1—C2	113.69 (7)	C6—C7—C8	121.01 (9)
N1—C1—H1A	108.8	C6—C7—H7	119.5
C2—C1—H1A	108.8	C8—C7—H7	119.5
N1—C1—H1B	108.8	C7—C8—C3	119.13 (8)
C2—C1—H1B	108.8	C7—C8—C10	119.87 (8)
H1A—C1—H1B	107.7	C3—C8—C10	120.99 (8)
N2—C2—C1	109.91 (7)	C4—C9—H9A	109.5
N2—C2—H2A	109.7	C4—C9—H9B	109.5
C1—C2—H2A	109.7	H9A—C9—H9B	109.5
N2—C2—H2B	109.7	C4—C9—H9C	109.5
C1—C2—H2B	109.7	H9A—C9—H9C	109.5
H2A—C2—H2B	108.2	H9B—C9—H9C	109.5
C4—C3—C8	120.33 (8)	C8—C10—H10A	109.5
C4—C3—N2	119.34 (8)	C8—C10—H10B	109.5
C8—C3—N2	120.30 (8)	H10A—C10—H10B	109.5
C5—C4—C3	118.71 (8)	C8—C10—H10C	109.5
C5—C4—C9	120.02 (8)	H10A—C10—H10C	109.5
C3—C4—C9	121.26 (8)	H10B—C10—H10C	109.5
C6—C5—C4	121.41 (9)	C1ⁱ—N1—C1	110.54 (6)
C6—C5—H5	119.3	C1ⁱ—N1—C1ⁱⁱ	110.54 (6)
C4—C5—H5	119.3	C1—N1—C1ⁱⁱ	110.54 (6)
C5—C6—C7	119.38 (9)	C3—N2—C2	116.04 (7)
C5—C6—H6	120.3	C3—N2—H2N	110.0 (9)
C7—C6—H6	120.3	C2—N2—H2N	109.3 (9)

N1—C1—C2—N2	54.02 (10)	C6—C7—C8—C10	−179.46 (9)
C8—C3—C4—C5	−1.51 (13)	C4—C3—C8—C7	0.65 (13)
N2—C3—C4—C5	−179.24 (8)	N2—C3—C8—C7	178.35 (8)
C8—C3—C4—C9	177.26 (8)	C4—C3—C8—C10	−179.19 (9)
N2—C3—C4—C9	−0.47 (13)	N2—C3—C8—C10	−1.48 (14)
C3—C4—C5—C6	1.07 (14)	C2—C1—N1—C1ⁱ	67.79 (13)
C9—C4—C5—C6	−177.72 (9)	C2—C1—N1—C1ⁱⁱ	−169.49 (8)
C4—C5—C6—C7	0.25 (14)	C4—C3—N2—C2	−74.71 (11)
C5—C6—C7—C8	−1.16 (14)	C8—C3—N2—C2	107.56 (10)
C6—C7—C8—C3	0.70 (14)	C1—C2—N2—C3	177.64 (7)

Symmetry codes: (i) −y+1, x−y, z; (ii) −x+y+1, −x+1, z.

Experimental details

Crystal data
Chemical formula	C₃₀H₄₂N₄
M_r	458.68
Crystal system, space group	Trigonal, R3
Temperature (K)	100
a, c (Å)	14.2880 (7), 22.3811 (11)
V (Å³)	3956.9 (5)
Z	6
Radiation type	Mo Kα
µ (mm⁻¹)	0.07
Crystal size (mm)	0.1 × 0.1 × 0.1

Data collection
Diffractometer	Bruker Smart APEXII CCD
Absorption correction	Multi-scan (SADABS; Sheldrick, 2009)
T_min, T_max	0.680, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	20390, 2695, 2330
R_int	0.031
(sin θ/λ)_max (Å⁻¹)	0.716

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.041, 0.113, 1.06
No. of reflections	2695
No. of parameters	109
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.42, −0.18

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999).

Acknowledgements

This material is based upon work supported by the US Department of Energy, Office of Basic Energy Science, grant No. DE—FG02–06ER15799. X-ray diffraction instrumentation was purchased with the help of funding from the National Science Foundation (CHE-0946721).

References

Almesåker, A., Gamez, P., Scott, J. L., Teat, S. J., Reedijk, J. & Spiccia, L. (2010). Eur. J. Inorg. Chem. pp. 5394–5400. Google Scholar
Almesåker, A., Scott, J. L., Spiccia, L. & Strauss, C. R. (2009). Tetrahedron Lett. 50, 1847–1850. Google Scholar
Amoroso, A. J., Edwards, P. G., Howard, S. T., Kariuki, B. M., Knight, J. C., Ooi, L., Malik, K. M. A., Stratford, L. & Al-Sudani, A.-R. H. (2009). Dalton Trans. 39, 8356–8362. Web of Science CSD CrossRef PubMed Google Scholar
Bruker (2009). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Morton, C., Gillespie, K. M., Sanders, C. J. & Scott, P. (2000). J. Organomet. Chem. 606, 141–146. Web of Science CrossRef CAS Google Scholar
Reithofer, M. R., Schrock, R. R. & Müller, P. (2010). J. Am. Chem. Soc. 132, 8349–8358. Web of Science CSD CrossRef CAS PubMed Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2009). SADABS. University of Göttingen, Germany. Google Scholar
Smythe, N. C., Schrock, R. R., Müller, P. & Weare, W. W. (2006). Inorg. Chem. 45, 9197–9205. Web of Science CSD CrossRef PubMed CAS Google Scholar
Yandulov, D. V. & Schrock, R. R. (2005). Inorg. Chem. 44, 1103–1117. Web of Science CSD CrossRef PubMed CAS Google Scholar