1,3,3-Tribenzyl­indolin-2-one

Liu, Y.; Liu, B.; Dong, Z.; Jin, S.

doi:10.1107/S1600536811042425

organic compounds

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ISSN: 2056-9890

Volume 67| Part 11| November 2011| Page o2998

doi:10.1107/S1600536811042425

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1,3,3-Tribenzylindolin-2-one

Yufang Liu,^a Bo Liu,^b ^* Zhenming Dong ^a and Shuo Jin ^a

^aSchool of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, Shanxi Province, People's Republic of China, and ^bSchool of Science, Beijing Jiaotong University, Beijing 100044, People's Republic of China
^*Correspondence e-mail: liuyf@sxu.edu.cn

(Received 3 October 2011; accepted 13 October 2011; online 22 October 2011)

In the title compound, C₂₉H₂₅NO, the dihedral angles between the indolin-2-one ring system and the three benzene rings are 62.78 (9), 31.69 (9) and 80.94 (9)°.

Related literature

For general background to the use of indoline-2-one compounds as precursors for the synthesis of antitumor agents, see: Wang et al. (2011 ). For a related structure, see: Katritzky et al. (1997 ).

Experimental

Crystal data

C₂₉H₂₅NO
M_r = 403.50
Monoclinic, P 2₁
a = 8.3387 (9) Å
b = 9.6266 (10) Å
c = 13.9398 (14) Å
β = 99.442 (2)°
V = 1103.8 (2) Å³
Z = 2
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 296 K
0.30 × 0.20 × 0.20 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ) T_min = 0.979, T_max = 0.986
4797 measured reflections
2073 independent reflections
1731 reflections with I > 2σ(I)
R_int = 0.028

Refinement

R[F² > 2σ(F²)] = 0.033
wR(F²) = 0.076
S = 1.05
2073 reflections
281 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.10 e Å⁻³
Δρ_min = −0.11 e Å⁻³

Data collection: SMART (Siemens, 1996 ); cell refinement: SAINT (Siemens, 1996); 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: SHELXL97.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811042425/hg5107sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811042425/hg5107Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536811042425/hg5107Isup3.cml

checkCIF report

Comment top

Indoline-2-one compounds have been widely explored as precursors for the synthesis of antitumor agent (Wang et al., 2011). In the course of exploring new antitumor medicine, we obtained a intermediate compound C₂₉H₂₅NO (I), the synthesis and structure of which are reported here.

The title compound contain four ring planes, three benzene rings and one indoline-2-one ring. The interplanar dihedral angle between the indolin-2-one ring plane and the three benzene ring planes are 62.78 (9)°, 31.69 (9)° and 80.94 (9)\ respectively.

The molecules of (I) crystallize in the space group P2₁ which is different from that of 3-(1,2-diphenylethylidene)indolin-2-one (P-1) (Katritzky et al. 1997).

Related literature top

For general background to the use of indoline-2-one compounds as precursors

for the synthesis of antitumor agents, see: Wang et al. (2011). For a related structure, see: Katritzky et al. (1997).

Experimental top

Indolin-2-one (0.50 g, 3.76 mmol) was dissolved in THF (20 mL) and KOH (0.80 g, 14.3 mmol) was slowly added. After heating the stirred mixture at reflux temperature for 30 min, a solution of 1-(chloromethyl)benzene (2.00 g, 15.9 mmol) in THF was slowly added and the refluxing continued for 2 h. The mixture was then cooled to 333 K and poured into water (200 mL) and was extracted with chloroform and dried over Na₂SO₄. After removing the solvent, the crude product was purified by column chromatography on silica gel, affording the title compound (yield: 0.23 g, 15%). The compound was then dissolved in THF, and colorless crystals were formed on slow evaporation at room temperature over one week.

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT (Siemens, 1996); 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: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. The molecular packing of (I) viewed along the b axis.

1,3,3-Tribenzylindolin-2-one top

Crystal data top

C₂₉H₂₅NO	F(000) = 428
M_r = 403.50	D_x = 1.214 Mg m⁻³
Monoclinic, P2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 2492 reflections
a = 8.3387 (9) Å	θ = 2.9–26.3°
b = 9.6266 (10) Å	µ = 0.07 mm⁻¹
c = 13.9398 (14) Å	T = 296 K
β = 99.442 (2)°	Block, yellow
V = 1103.8 (2) Å³	0.30 × 0.20 × 0.20 mm
Z = 2

Data collection top

Bruker SMART APEX CCD area-detector diffractometer	2073 independent reflections
Radiation source: fine-focus sealed tube	1731 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.028
phi and ω scans	θ_max = 25.1°, θ_min = 1.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −9→7
T_min = 0.979, T_max = 0.986	k = −11→11
4797 measured reflections	l = −16→16

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.033	H-atom parameters constrained
wR(F²) = 0.076	w = 1/[σ²(F_o²) + (0.0404P)²] where P = (F_o² + 2F_c²)/3
S = 1.05	(Δ/σ)_max < 0.001
2073 reflections	Δρ_max = 0.10 e Å⁻³
281 parameters	Δρ_min = −0.11 e Å⁻³
1 restraint	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.085 (5)

Crystal data top

C₂₉H₂₅NO	V = 1103.8 (2) Å³
M_r = 403.50	Z = 2
Monoclinic, P2₁	Mo Kα radiation
a = 8.3387 (9) Å	µ = 0.07 mm⁻¹
b = 9.6266 (10) Å	T = 296 K
c = 13.9398 (14) Å	0.30 × 0.20 × 0.20 mm
β = 99.442 (2)°

Data collection top

Bruker SMART APEX CCD area-detector diffractometer	2073 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	1731 reflections with I > 2σ(I)
T_min = 0.979, T_max = 0.986	R_int = 0.028
4797 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.033	1 restraint
wR(F²) = 0.076	H-atom parameters constrained
S = 1.05	Δρ_max = 0.10 e Å⁻³
2073 reflections	Δρ_min = −0.11 e Å⁻³
281 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
O1	0.3706 (2)	−0.1015 (2)	0.38221 (12)	0.0693 (5)
N1	0.5070 (2)	−0.1315 (2)	0.25382 (12)	0.0454 (5)
C24	0.3103 (3)	−0.1520 (2)	0.09974 (16)	0.0446 (6)
C8	0.6583 (2)	−0.0925 (2)	0.23014 (14)	0.0415 (5)
C3	0.7426 (3)	−0.0128 (2)	0.30485 (14)	0.0393 (5)
C16	0.7158 (3)	−0.0745 (3)	0.48023 (15)	0.0519 (6)
H16A	0.6343	−0.0772	0.5225	0.062*
H16B	0.7383	−0.1698	0.4640	0.062*
C10	0.4948 (3)	0.2266 (2)	0.32102 (16)	0.0464 (6)
C15	0.3277 (3)	0.2368 (3)	0.31634 (18)	0.0558 (7)
H15	0.2784	0.1947	0.3640	0.067*
C4	0.8954 (3)	0.0370 (3)	0.29641 (17)	0.0503 (6)
H4	0.9531	0.0917	0.3452	0.060*
C2	0.6413 (3)	0.0012 (2)	0.38491 (15)	0.0437 (6)
C1	0.4884 (3)	−0.0807 (3)	0.34282 (16)	0.0468 (6)
C25	0.3007 (3)	−0.0100 (3)	0.08741 (17)	0.0524 (6)
H25	0.3496	0.0480	0.1371	0.063*
C17	0.8693 (3)	−0.0135 (2)	0.53710 (15)	0.0488 (6)
C23	0.3890 (3)	−0.2184 (3)	0.19369 (17)	0.0574 (7)
H23A	0.3046	−0.2437	0.2308	0.069*
H23B	0.4424	−0.3033	0.1787	0.069*
C18	1.0215 (3)	−0.0589 (3)	0.52212 (17)	0.0612 (7)
H18	1.0286	−0.1267	0.4755	0.073*
C9	0.5968 (3)	0.1523 (3)	0.40544 (16)	0.0504 (6)
H9A	0.5382	0.1527	0.4601	0.060*
H9B	0.6965	0.2043	0.4247	0.060*
C22	0.8643 (3)	0.0867 (3)	0.60759 (16)	0.0566 (7)
H22	0.7641	0.1195	0.6188	0.068*
C6	0.8748 (3)	−0.0747 (3)	0.14105 (18)	0.0610 (7)
H6	0.9211	−0.0958	0.0865	0.073*
C29	0.2389 (3)	−0.2353 (3)	0.02380 (18)	0.0629 (7)
H29	0.2455	−0.3314	0.0302	0.075*
C26	0.2199 (3)	0.0472 (3)	0.0027 (2)	0.0668 (8)
H26	0.2133	0.1432	−0.0042	0.080*
C7	0.7211 (3)	−0.1231 (3)	0.14706 (16)	0.0547 (6)
H7	0.6619	−0.1745	0.0969	0.066*
C11	0.5633 (3)	0.2891 (3)	0.24806 (17)	0.0578 (7)
H11	0.6752	0.2844	0.2500	0.069*
C21	1.0043 (4)	0.1389 (3)	0.66143 (19)	0.0682 (8)
H21	0.9976	0.2061	0.7085	0.082*
C12	0.4683 (3)	0.3586 (3)	0.1721 (2)	0.0697 (8)
H12	0.5161	0.3982	0.1229	0.084*
C20	1.1531 (4)	0.0928 (3)	0.6464 (2)	0.0698 (8)
H20	1.2474	0.1271	0.6838	0.084*
C5	0.9610 (3)	0.0040 (3)	0.21408 (18)	0.0580 (7)
H5	1.0644	0.0355	0.2083	0.070*
C28	0.1581 (3)	−0.1783 (4)	−0.0613 (2)	0.0754 (9)
H28	0.1100	−0.2359	−0.1114	0.090*
C14	0.2335 (3)	0.3088 (3)	0.2416 (2)	0.0639 (7)
H14	0.1220	0.3166	0.2403	0.077*
C13	0.3036 (3)	0.3686 (3)	0.1697 (2)	0.0684 (8)
H13	0.2396	0.4160	0.1192	0.082*
C19	1.1621 (3)	−0.0052 (3)	0.5751 (2)	0.0710 (8)
H19	1.2629	−0.0350	0.5628	0.085*
C27	0.1485 (3)	−0.0374 (4)	−0.0721 (2)	0.0730 (9)
H27	0.0942	0.0012	−0.1296	0.088*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0624 (10)	0.0862 (14)	0.0635 (10)	−0.0224 (10)	0.0228 (9)	−0.0056 (11)
N1	0.0469 (11)	0.0475 (12)	0.0406 (10)	−0.0077 (9)	0.0037 (8)	−0.0046 (9)
C24	0.0411 (12)	0.0487 (15)	0.0428 (13)	−0.0069 (11)	0.0039 (10)	−0.0058 (11)
C8	0.0445 (12)	0.0402 (13)	0.0387 (11)	0.0010 (11)	0.0037 (10)	0.0007 (11)
C3	0.0425 (12)	0.0363 (12)	0.0375 (11)	0.0003 (10)	0.0016 (9)	0.0013 (10)
C16	0.0670 (15)	0.0468 (14)	0.0406 (12)	−0.0041 (13)	0.0048 (11)	0.0017 (12)
C10	0.0506 (14)	0.0403 (13)	0.0462 (13)	0.0024 (11)	0.0014 (11)	−0.0099 (11)
C15	0.0539 (15)	0.0581 (16)	0.0539 (14)	−0.0019 (13)	0.0041 (12)	−0.0131 (14)
C4	0.0485 (14)	0.0491 (15)	0.0516 (14)	−0.0032 (11)	0.0027 (11)	0.0018 (12)
C2	0.0498 (13)	0.0458 (14)	0.0346 (11)	−0.0052 (11)	0.0048 (10)	−0.0015 (11)
C1	0.0499 (13)	0.0468 (14)	0.0434 (12)	−0.0058 (12)	0.0067 (11)	0.0027 (12)
C25	0.0567 (15)	0.0540 (16)	0.0462 (14)	−0.0064 (12)	0.0073 (11)	−0.0014 (13)
C17	0.0633 (15)	0.0434 (14)	0.0367 (11)	0.0057 (12)	−0.0003 (11)	0.0033 (11)
C23	0.0633 (16)	0.0510 (16)	0.0540 (14)	−0.0171 (13)	−0.0019 (12)	−0.0020 (13)
C18	0.0718 (17)	0.0545 (16)	0.0521 (15)	0.0139 (14)	−0.0049 (13)	−0.0046 (13)
C9	0.0571 (14)	0.0504 (15)	0.0425 (13)	0.0005 (12)	0.0047 (11)	−0.0086 (12)
C22	0.0729 (17)	0.0547 (16)	0.0402 (13)	0.0072 (13)	0.0035 (12)	−0.0010 (13)
C6	0.0639 (16)	0.0716 (18)	0.0511 (13)	0.0114 (15)	0.0203 (13)	−0.0025 (14)
C29	0.0678 (17)	0.0570 (17)	0.0587 (16)	−0.0054 (14)	−0.0047 (13)	−0.0108 (14)
C26	0.0690 (17)	0.0654 (18)	0.0652 (18)	−0.0027 (15)	0.0081 (14)	0.0138 (15)
C7	0.0608 (15)	0.0583 (16)	0.0446 (12)	0.0040 (13)	0.0075 (11)	−0.0074 (13)
C11	0.0532 (15)	0.0559 (16)	0.0630 (16)	−0.0005 (13)	0.0061 (13)	0.0048 (14)
C21	0.095 (2)	0.0543 (16)	0.0498 (15)	−0.0009 (16)	−0.0057 (15)	−0.0088 (14)
C12	0.0756 (19)	0.0597 (17)	0.0717 (17)	0.0039 (15)	0.0063 (15)	0.0158 (15)
C20	0.0749 (19)	0.0567 (18)	0.0686 (18)	−0.0057 (15)	−0.0152 (15)	0.0032 (16)
C5	0.0512 (14)	0.0616 (17)	0.0641 (16)	0.0033 (13)	0.0176 (13)	0.0075 (14)
C28	0.077 (2)	0.089 (2)	0.0528 (17)	−0.0057 (18)	−0.0112 (14)	−0.0182 (17)
C14	0.0502 (15)	0.0652 (17)	0.0713 (17)	0.0067 (14)	−0.0049 (13)	−0.0105 (15)
C13	0.0723 (19)	0.0517 (16)	0.0732 (18)	0.0061 (15)	−0.0120 (15)	0.0052 (16)
C19	0.0628 (17)	0.0706 (19)	0.0736 (17)	0.0133 (15)	−0.0062 (14)	0.0036 (17)
C27	0.0704 (19)	0.097 (3)	0.0476 (15)	0.0017 (17)	−0.0012 (13)	0.0128 (17)

Geometric parameters (Å, º) top

O1—C1	1.218 (3)	C18—C19	1.380 (4)
N1—C1	1.366 (3)	C18—H18	0.9300
N1—C8	1.407 (3)	C9—H9A	0.9700
N1—C23	1.449 (3)	C9—H9B	0.9700
C24—C25	1.379 (3)	C22—C21	1.375 (3)
C24—C29	1.383 (3)	C22—H22	0.9300
C24—C23	1.507 (3)	C6—C5	1.374 (4)
C8—C7	1.379 (3)	C6—C7	1.380 (3)
C8—C3	1.388 (3)	C6—H6	0.9300
C3—C4	1.384 (3)	C29—C28	1.379 (4)
C3—C2	1.512 (3)	C29—H29	0.9300
C16—C17	1.510 (3)	C26—C27	1.379 (4)
C16—C2	1.553 (3)	C26—H26	0.9300
C16—H16A	0.9700	C7—H7	0.9300
C16—H16B	0.9700	C11—C12	1.386 (3)
C10—C11	1.383 (3)	C11—H11	0.9300
C10—C15	1.388 (3)	C21—C20	1.366 (4)
C10—C9	1.514 (3)	C21—H21	0.9300
C15—C14	1.384 (3)	C12—C13	1.372 (4)
C15—H15	0.9300	C12—H12	0.9300
C4—C5	1.387 (3)	C20—C19	1.381 (4)
C4—H4	0.9300	C20—H20	0.9300
C2—C1	1.532 (3)	C5—H5	0.9300
C2—C9	1.539 (3)	C28—C27	1.365 (4)
C25—C26	1.375 (3)	C28—H28	0.9300
C25—H25	0.9300	C14—C13	1.367 (4)
C17—C22	1.383 (3)	C14—H14	0.9300
C17—C18	1.389 (3)	C13—H13	0.9300
C23—H23A	0.9700	C19—H19	0.9300
C23—H23B	0.9700	C27—H27	0.9300

C1—N1—C8	110.93 (17)	C10—C9—C2	115.07 (18)
C1—N1—C23	124.39 (19)	C10—C9—H9A	108.5
C8—N1—C23	124.65 (19)	C2—C9—H9A	108.5
C25—C24—C29	118.1 (2)	C10—C9—H9B	108.5
C25—C24—C23	122.5 (2)	C2—C9—H9B	108.5
C29—C24—C23	119.4 (2)	H9A—C9—H9B	107.5
C7—C8—C3	122.2 (2)	C21—C22—C17	121.4 (3)
C7—C8—N1	128.2 (2)	C21—C22—H22	119.3
C3—C8—N1	109.58 (17)	C17—C22—H22	119.3
C4—C3—C8	119.18 (19)	C5—C6—C7	121.3 (2)
C4—C3—C2	131.7 (2)	C5—C6—H6	119.3
C8—C3—C2	109.10 (17)	C7—C6—H6	119.3
C17—C16—C2	116.90 (19)	C28—C29—C24	121.1 (3)
C17—C16—H16A	108.1	C28—C29—H29	119.5
C2—C16—H16A	108.1	C24—C29—H29	119.5
C17—C16—H16B	108.1	C25—C26—C27	120.2 (3)
C2—C16—H16B	108.1	C25—C26—H26	119.9
H16A—C16—H16B	107.3	C27—C26—H26	119.9
C11—C10—C15	117.9 (2)	C8—C7—C6	117.6 (2)
C11—C10—C9	122.0 (2)	C8—C7—H7	121.2
C15—C10—C9	120.1 (2)	C6—C7—H7	121.2
C14—C15—C10	120.8 (3)	C10—C11—C12	121.2 (2)
C14—C15—H15	119.6	C10—C11—H11	119.4
C10—C15—H15	119.6	C12—C11—H11	119.4
C3—C4—C5	119.0 (2)	C20—C21—C22	120.6 (3)
C3—C4—H4	120.5	C20—C21—H21	119.7
C5—C4—H4	120.5	C22—C21—H21	119.7
C3—C2—C1	101.66 (17)	C13—C12—C11	119.8 (3)
C3—C2—C9	113.73 (18)	C13—C12—H12	120.1
C1—C2—C9	110.30 (19)	C11—C12—H12	120.1
C3—C2—C16	113.32 (18)	C21—C20—C19	119.4 (3)
C1—C2—C16	106.07 (17)	C21—C20—H20	120.3
C9—C2—C16	111.05 (18)	C19—C20—H20	120.3
O1—C1—N1	124.8 (2)	C6—C5—C4	120.7 (2)
O1—C1—C2	126.4 (2)	C6—C5—H5	119.7
N1—C1—C2	108.73 (19)	C4—C5—H5	119.7
C26—C25—C24	120.9 (2)	C27—C28—C29	120.2 (3)
C26—C25—H25	119.5	C27—C28—H28	119.9
C24—C25—H25	119.5	C29—C28—H28	119.9
C22—C17—C18	117.4 (2)	C13—C14—C15	120.3 (2)
C22—C17—C16	121.5 (2)	C13—C14—H14	119.8
C18—C17—C16	121.0 (2)	C15—C14—H14	119.8
N1—C23—C24	114.57 (19)	C14—C13—C12	119.9 (3)
N1—C23—H23A	108.6	C14—C13—H13	120.0
C24—C23—H23A	108.6	C12—C13—H13	120.0
N1—C23—H23B	108.6	C20—C19—C18	119.9 (3)
C24—C23—H23B	108.6	C20—C19—H19	120.0
H23A—C23—H23B	107.6	C18—C19—H19	120.0
C19—C18—C17	121.3 (3)	C28—C27—C26	119.5 (3)
C19—C18—H18	119.4	C28—C27—H27	120.2
C17—C18—H18	119.4	C26—C27—H27	120.2

Experimental details

Crystal data
Chemical formula	C₂₉H₂₅NO
M_r	403.50
Crystal system, space group	Monoclinic, P2₁
Temperature (K)	296
a, b, c (Å)	8.3387 (9), 9.6266 (10), 13.9398 (14)
β (°)	99.442 (2)
V (Å³)	1103.8 (2)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.07
Crystal size (mm)	0.30 × 0.20 × 0.20

Data collection
Diffractometer	Bruker SMART APEX CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996)
T_min, T_max	0.979, 0.986
No. of measured, independent and observed [I > 2σ(I)] reflections	4797, 2073, 1731
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.596

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.033, 0.076, 1.05
No. of reflections	2073
No. of parameters	281
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.10, −0.11

Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1996), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997).

Acknowledgements

The authors are grateful to the National Science Foundation (BL, No. 21072019) for support of this work and Dr Maosen Yuan of Northwest A & F University for the data collection and structure determination.

References

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