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Acta Cryst. (2008). E64, m129-m130    [ doi:10.1107/S1600536807065208 ]

([mu]-4-Bromo-2-{1-[2-(dimethylamino)ethylimino]ethyl}phenolato)bis[ethylzinc(II)]

W.-C. Hung, S.-L. Lai and C.-C. Lin

Abstract top

The title complex, [Zn2(C2H5)2(C12H16BrN2O)2], is dimeric, bridged through the O atoms of the phenolate anions. The molecule lies on a crystallographic twofold rotation axis. Each Zn atom is pentacoordinated by two N atoms and two bridging O atoms of the tridentate salicylideneiminate ligands and one C atom from an ethyl group, forming a distorted square-pyramidal environment.

Comment top

Poly(ε-caprolactone) (PCL) and poly(lactide) (PLA) and their copolymers have been attracting considerable attention due to their potential applications in many fields (Gref et al.,1994; Jeong et al., 1997). The major polymerization method employed to synthesize these polymers is the ring-opening polymerization (ROP) of lactones/lactides. Many zinc complexes with various ligands have been reported to be effective initiators/catalyst for ROP of lactones/lactides (Chamberlain et al., 2001; Williams et al., 2003; Dechy-Cabaret et al. 2004; Chen, et al., 2005, Wu, et al., 2005; Wu et al., 2006). Tripodal tridentate ligand supported zinc complexes have been synthesized and used for the polymerization of lactides and the polymerizations are living with relatively low polydispersities (Chisholm et al., 2000). Recently, we have synthesized a series of Schiff base zinc complexes which have shown high activity in the ROP of lactide (Chen et al., 2006). We report herein the synthesis and crystal structure of a NNO-tridentate Schifff base zinc complex (I), a potential catalyst for lactide polymerization.

The solid structure of (I) reveals a dimeric Zn(II) complex (Fig. 1.) containing a Zn2O2 core bridging through the oxygen atoms of the phenolate. The geometry around Zn atom is pentacoordinated with a distorted square pyramid geometry in which two nitrogen atoms and two oxygen atoms are almost coplanar occupied the basal positions. The ethyl group is sitting on the axial position. The zinc atom is ca 0.888 Å above the O1/O1A/N1/N2 mean plane. The distances between the Zn atom and O1, O1A, N1, N2, and C13 are 2.142 (3), 2.060 (3), 2.180 (4), 2.236 (4), 2.022 (4) Å, respectively, which are all within a normal range for Schiff base Zn(II) complexes (Chen et al., 2006).

Related literature top

For related literature, see: Chamberlain et al. (2001); Chen et al. (2005, 2006); Chisholm et al. (2000); Dechy-Cabaret et al. (2004); Gref et al. (1994); Jeong et al. (1997); Williams et al. (2003); Wu et al. (2005, 2006).

Experimental top

The ligand, 4-bromo-2-[1-(2-dimethylamino-ethylimino)ethyl]phenol was prepared by the reaction of 2-dimethylaminoethylamine (1.39 g, 22 mmol) with 5-bromo-2-hydroxyacetophenone (4.30 g, 20 mmol) in ethanol (30 ml) at room temperature for 24 h. Volatile materials were removed under vacuum and the resulting material was dissolved in hot hexane (30 ml). The solution was then cooled at 250 K for 24 h giving yellow powder.

The title complex was synthesized by the following procedures. To an ice cold solution (273 K) of 4-bromo-2-[1-(2-dimethylamino-ethylimino)ethyl]phenol (0.57 g, 2.0 mmol) in 40 ml hexane was slowly added a diethyl zinc (2.2 ml, 1 M in hexane, 2.2 mmol) solution. The mixture was stirred at room temoerature for 3 h during which the formation of yellow precipitate was observed. The resulting solid was collected by filtration and then dried under vacuum to give yellow powder. Yellow crystals was obtained from the recrystallization of a mixed dichloromethane/hexane solution.

Refinement top

All non-H atoms were initially located in a difference Fourier map. The methyl H atoms were then constrained to an ideal geometry with C—H distances of 0.96 Å and Uiso(H) = 1.5Ueq(C), but each group was allowed to rotate freely about its C—C bond. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C—H distances in the range 0.95–1.00 Å and Uiso(H) =1.2Ueq(C).

Computing details top

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1999); software used to prepare material for publication: SHELXTL (Bruker, 1999).

Figures top
[Figure 1] Fig. 1. A view of the molecular structure of (I) with displacement ellipsoids shown at the 20% probability level.
(µ-4-Bromo-2-{1-[2-(dimethylamino)ethylimino]ethyl}phenolato)bis[ethylzinc(II)] top
Crystal data top
[Zn2(C2H5)2(C12H16BrN2O)2]F000 = 1536
Mr = 757.22Dx = 1.550 Mg m−3
Orthorhombic, PbcnMo Kα radiation
λ = 0.71073 Å
Hall symbol: -P 2n 2abCell parameters from 3732 reflections
a = 21.656 (6) Åθ = 2.8–24.0º
b = 7.839 (2) ŵ = 3.97 mm−1
c = 19.114 (5) ÅT = 293 (2) K
V = 3244.9 (14) Å3Parallelpiped, yellow
Z = 40.17 × 0.16 × 0.15 mm
Data collection top
Bruker SMART 1K CCD
diffractometer		1957 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.086
Monochromator: graphiteθmax = 26.1º
T = 298(2) Kθmin = 1.9º
φ and ω scansh = −26→25
Absorption correction: nonek = −9→9
17313 measured reflectionsl = −13→23
3207 independent reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.040H-atom parameters constrained
wR(F2) = 0.107  w = 1/[σ2(Fo2) + (0.052P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.00(Δ/σ)max = 0.002
3207 reflectionsΔρmax = 0.68 e Å−3
172 parametersΔρmin = −0.39 e Å−3
Primary atom site location: structure-invariant direct methodsExtinction correction: none
Crystal data top
[Zn2(C2H5)2(C12H16BrN2O)2]V = 3244.9 (14) Å3
Mr = 757.22Z = 4
Orthorhombic, PbcnMo Kα
a = 21.656 (6) ŵ = 3.97 mm−1
b = 7.839 (2) ÅT = 293 (2) K
c = 19.114 (5) Å0.17 × 0.16 × 0.15 mm
Data collection top
Bruker SMART 1K CCD
diffractometer		3207 independent reflections
Absorption correction: none1957 reflections with I > 2σ(I)
17313 measured reflectionsRint = 0.086
Refinement top
R[F2 > 2σ(F2)] = 0.040172 parameters
wR(F2) = 0.107H-atom parameters constrained
S = 1.00Δρmax = 0.68 e Å−3
3207 reflectionsΔρmin = −0.39 e Å−3
Special details top

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
Zn0.93264 (2)0.18811 (6)0.70779 (3)0.04040 (17)
Br0.79595 (3)0.47079 (8)1.01986 (3)0.0781 (2)
O10.97357 (12)0.1816 (4)0.80980 (15)0.0476 (8)
N10.87340 (16)0.0062 (4)0.7620 (2)0.0462 (9)
N20.92031 (17)−0.0132 (5)0.6261 (2)0.0569 (10)
C10.93610 (19)0.2386 (6)0.8581 (2)0.0424 (10)
C20.87745 (18)0.1621 (5)0.8681 (2)0.0395 (10)
C30.8368 (2)0.2322 (6)0.9182 (2)0.0461 (11)
H3A0.79840.18210.92540.055*
C40.8534 (2)0.3742 (6)0.9567 (2)0.0536 (12)
C50.9115 (2)0.4456 (6)0.9490 (3)0.0613 (14)
H5A0.92310.53870.97610.074*
C60.9519 (2)0.3770 (6)0.9005 (3)0.0566 (13)
H6A0.99110.42470.89610.068*
C70.85761 (18)0.0141 (5)0.8261 (3)0.0428 (10)
C80.8185 (3)−0.1206 (7)0.8618 (3)0.0779 (17)
H8A0.8087−0.20920.82890.117*
H8B0.7810−0.06970.87860.117*
H8C0.8410−0.16830.90030.117*
C90.8539 (2)−0.1357 (6)0.7177 (3)0.0655 (15)
H9A0.8114−0.16530.72790.079*
H9B0.8795−0.23480.72690.079*
C100.8600 (2)−0.0839 (7)0.6419 (3)0.0780 (18)
H10A0.8529−0.18270.61250.094*
H10B0.82860.00020.63100.094*
C110.9207 (3)0.0648 (9)0.5561 (3)0.104 (2)
H11A0.9154−0.02230.52130.156*
H11B0.95930.12190.54860.156*
H11C0.88750.14570.55260.156*
C120.9678 (3)−0.1460 (7)0.6266 (4)0.092 (2)
H12A0.9593−0.22740.59030.138*
H12B0.9677−0.20260.67110.138*
H12C1.0075−0.09520.61860.138*
C130.88570 (19)0.4061 (5)0.6884 (2)0.0469 (11)
H13A0.90590.49860.71320.056*
H13B0.88850.43070.63880.056*
C140.8200 (2)0.4042 (8)0.7084 (3)0.0851 (19)
H14A0.80160.51210.69700.128*
H14B0.81650.38430.75780.128*
H14C0.79920.31500.68340.128*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Zn0.0380 (3)0.0341 (3)0.0490 (3)0.0014 (2)−0.0007 (2)−0.0017 (2)
Br0.0802 (4)0.0978 (5)0.0562 (4)0.0351 (3)−0.0039 (3)−0.0238 (3)
O10.0353 (15)0.0560 (19)0.052 (2)0.0020 (14)0.0015 (13)−0.0005 (15)
N10.047 (2)0.032 (2)0.061 (3)−0.0057 (16)0.0050 (18)−0.0076 (18)
N20.060 (3)0.055 (2)0.055 (3)−0.012 (2)0.0055 (19)−0.019 (2)
C10.046 (2)0.044 (2)0.037 (3)0.006 (2)−0.005 (2)0.002 (2)
C20.043 (2)0.037 (2)0.039 (2)0.0009 (19)0.0002 (19)0.0008 (19)
C30.045 (2)0.051 (3)0.042 (3)0.003 (2)0.001 (2)0.002 (2)
C40.056 (3)0.062 (3)0.043 (3)0.020 (2)−0.003 (2)−0.005 (2)
C50.069 (3)0.051 (3)0.064 (4)0.001 (3)−0.016 (3)−0.012 (3)
C60.050 (3)0.056 (3)0.064 (4)−0.006 (2)−0.006 (2)−0.007 (3)
C70.041 (2)0.035 (2)0.052 (3)−0.0002 (19)0.007 (2)0.001 (2)
C80.083 (4)0.068 (4)0.083 (4)−0.030 (3)0.024 (3)0.003 (3)
C90.072 (3)0.046 (3)0.078 (4)−0.022 (3)0.015 (3)−0.025 (3)
C100.065 (4)0.079 (4)0.089 (5)−0.029 (3)0.006 (3)−0.041 (3)
C110.143 (6)0.114 (5)0.054 (4)−0.046 (5)0.003 (4)−0.021 (4)
C120.083 (4)0.065 (4)0.128 (6)0.003 (3)0.020 (4)−0.032 (4)
C130.046 (2)0.029 (2)0.066 (3)0.0080 (19)−0.010 (2)0.003 (2)
C140.073 (4)0.063 (4)0.119 (5)0.021 (3)0.015 (4)0.027 (4)
Geometric parameters (Å, °) top
Zn—C132.022 (4)C6—H6A0.9300
Zn—O1i2.060 (3)C7—C81.516 (6)
Zn—O12.142 (3)C8—H8A0.9600
Zn—N12.180 (4)C8—H8B0.9600
Zn—N22.236 (4)C8—H8C0.9600
Br—C41.892 (4)C9—C101.509 (7)
O1—C11.307 (5)C9—H9A0.9700
O1—Zni2.060 (3)C9—H9B0.9700
N1—C71.273 (5)C10—H10A0.9700
N1—C91.460 (6)C10—H10B0.9700
N2—C101.451 (6)C11—H11A0.9600
N2—C121.464 (6)C11—H11B0.9600
N2—C111.471 (7)C11—H11C0.9600
C1—C61.398 (6)C12—H12A0.9600
C1—C21.417 (6)C12—H12B0.9600
C2—C31.413 (6)C12—H12C0.9600
C2—C71.475 (6)C13—C141.472 (7)
C3—C41.382 (6)C13—H13A0.9700
C3—H3A0.9300C13—H13B0.9700
C4—C51.384 (6)C14—H14A0.9600
C5—C61.383 (7)C14—H14B0.9600
C5—H5A0.9300C14—H14C0.9600
C13—Zn—O1i119.14 (15)C7—C8—H8A109.5
C13—Zn—O1113.25 (15)C7—C8—H8B109.5
O1i—Zn—O174.93 (13)H8A—C8—H8B109.5
C13—Zn—N1110.12 (16)C7—C8—H8C109.5
O1i—Zn—N1129.91 (12)H8A—C8—H8C109.5
O1—Zn—N178.18 (13)H8B—C8—H8C109.5
C13—Zn—N2114.09 (17)N1—C9—C10109.1 (4)
O1i—Zn—N289.20 (13)N1—C9—H9A109.9
O1—Zn—N2131.93 (14)C10—C9—H9A109.9
N1—Zn—N278.48 (14)N1—C9—H9B109.9
C1—O1—Zni136.0 (3)C10—C9—H9B109.9
C1—O1—Zn112.2 (2)H9A—C9—H9B108.3
Zni—O1—Zn105.00 (13)N2—C10—C9112.4 (4)
C7—N1—C9121.2 (4)N2—C10—H10A109.1
C7—N1—Zn125.7 (3)C9—C10—H10A109.1
C9—N1—Zn113.1 (3)N2—C10—H10B109.1
C10—N2—C12111.1 (4)C9—C10—H10B109.1
C10—N2—C11110.7 (5)H10A—C10—H10B107.8
C12—N2—C11107.3 (5)N2—C11—H11A109.5
C10—N2—Zn103.4 (3)N2—C11—H11B109.5
C12—N2—Zn114.4 (3)H11A—C11—H11B109.5
C11—N2—Zn110.0 (3)N2—C11—H11C109.5
O1—C1—C6121.5 (4)H11A—C11—H11C109.5
O1—C1—C2120.4 (4)H11B—C11—H11C109.5
C6—C1—C2118.0 (4)N2—C12—H12A109.5
C3—C2—C1119.1 (4)N2—C12—H12B109.5
C3—C2—C7119.6 (4)H12A—C12—H12B109.5
C1—C2—C7121.4 (4)N2—C12—H12C109.5
C4—C3—C2120.8 (4)H12A—C12—H12C109.5
C4—C3—H3A119.6H12B—C12—H12C109.5
C2—C3—H3A119.6C14—C13—Zn115.4 (3)
C3—C4—C5120.4 (4)C14—C13—H13A108.4
C3—C4—Br119.4 (4)Zn—C13—H13A108.4
C5—C4—Br120.2 (4)C14—C13—H13B108.4
C4—C5—C6119.3 (5)Zn—C13—H13B108.4
C4—C5—H5A120.3H13A—C13—H13B107.5
C6—C5—H5A120.3C13—C14—H14A109.5
C1—C6—C5122.3 (4)C13—C14—H14B109.5
C1—C6—H6A118.8H14A—C14—H14B109.5
C5—C6—H6A118.8C13—C14—H14C109.5
N1—C7—C2118.9 (4)H14A—C14—H14C109.5
N1—C7—C8123.3 (4)H14B—C14—H14C109.5
C2—C7—C8117.8 (4)
Symmetry codes: (i) −x+2, y, −z+3/2.
Table 1
Selected geometric parameters (Å, °) top
Zn—C132.022 (4)Zn—N12.180 (4)
Zn—O1i2.060 (3)Zn—N22.236 (4)
Zn—O12.142 (3)
C13—Zn—O1i119.14 (15)O1—Zn—N178.18 (13)
C13—Zn—O1113.25 (15)C13—Zn—N2114.09 (17)
O1i—Zn—O174.93 (13)O1i—Zn—N289.20 (13)
C13—Zn—N1110.12 (16)O1—Zn—N2131.93 (14)
O1i—Zn—N1129.91 (12)N1—Zn—N278.48 (14)
Symmetry codes: (i) −x+2, y, −z+3/2.
Acknowledgements top

Financial support from the National Science Council of the Republic of China is gratefully appreciated.

references
References top

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