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The title compound, [Zn(C6H5)2(C5H5N)2], (I), forms conformationally chiral mol­ecules residing on a twofold axis. The mol­ecules are stacked along c, and these stacks are associated by edge-to-face π–π inter­actions. Crystals of (I) belong to the Sohncke space group P21212 and the crystal lattice of (I) is chiral. The crystal batch that was examined consisted of a mixture of enanti­omerically pure crystals and crystals twinned by inversion.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109014127/gg3194sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270109014127/gg3194Isup2.hkl
Contains datablock I

CCDC reference: 735112

Comment top

Optical resolution is usually time consuming (Faigl et al., 2008), but in a few rare cases spontaneous resolution may occur. It has been estimated to occur for less than 10% of crystalline racemates (Jacques et al., 1981) and involves the crystallization of a racemate in one of the 65 Sohncke space groups (Flack, 2003). Chiral molecules which are stereochemically labile in solution may undergo total spontaneous resolution, also known as crystallization-induced asymmetric transformation (Jacques et al., 1984). This is a phenomenon where the whole batch of crystals originates from a single-crystal nucleus and a fast enantiomerization in the solution converts all material in solution into the crystallizing enantiomer. Under favourable circumstances the entire amount of racemate may be converted to a pure enantiomer in quantitative yield. It has been observed that slow stirring may be beneficial for crystallization-induced asymmetric transformation (Kondepudi et al., 1990; McBride & Carter, 1991; Pagni & Compton, 2002). Since a racemic mixture is transformed into an optically active substance without the use of chiral reagents or catalysts, crystallization-induced asymmetric transformation is an important strategy for absolute asymmetric synthesis i.e. the creation of optically active substances from achiral or racemic starting materials only (Feringa & Van Delden, 1999). Over the years we have studied the total spontaneous resolution of stereochemically labile chemical reagents (Lennartson et al., 2009; Vestergren et al., 2000, 2003; Håkansson et al., 1999) and potential substrates (Johansson & Håkansson, 2005; Lennartson, Salo et al., 2005; Andersson et al., 1986, Lennartson et al., 2007). During a study of (diphenyl)zinc complexes, it was found that diphenyl(dipyridyl)zinc(II), (I), crystallizes in the Sohnke space group P21212.

The molecules of (I) are located on a twofold axis, and the molecules are therefore C2 symmetric. The coordination geometry around Zn1 is distorted tetrahedral (Fig. 1). The molecules of (I) are conformationally chiral due to the orientations of the aromatic rings surrounding the central Zn atom as in Fig. 2. The enantiomerization barrier between the two enantiomers can be expected to be very low, and the conformational chirality of (I) will be immediately lost upon dissolution of the crystals, one of the requirements for total spontaneous resolution.

Only a limited number of diphenylzinc structures are reported in the Cambridge Structural Database (CSD, version 5.29 of November 2007; Allen, 2002). Unsolvated diphenylzinc forms a dimer with two three-coordinate Zn atoms bridged by two phenyl groups (Markies et al., 1990). There are another five structures where diphenylzinc coordinates crown ethers (Markies et al., 1991; Fabicon et al., 1999; Kooijman et al., 2007), two examples of coordination to glyme ligands (Markies et al., 1992) and a complex with thiophene (Dickson et al., 2000). The thiophene complex is dimeric with two distorted tetrahedral Zn atoms bridged by two phenyl groups, and the structure is therefore very different from (I). The other seven complexes also differ from (I), since the C—Zn—C angles are considerably larger, approximately 140–150° compared with 125.65 (8)° in (I). The C—Zn—C angle in the (2)-(diphenyl)zinc(18-crown-6)rotaxane is 174.5 (1)° (Fabicon et al., 1999). These differences are rational, since pyridine appears to coordinate stronger than the ligands previously employed. The Zn—N distances in (I) are 2.1505 (12) Å, while the Zn—O distances in the rotaxane approaches 3 Å. Monomeric Lewis base free dialkylzinc compounds are reported to be linear (Almenningen et al., 1982; Lewinski et al., 2007), and this rule also applies to monomeric diarylzinc compounds, viz. dimesitylzinc (Cole et al., 2003). Weaker coordinating ligands would therefore be expected to give rise to larger C—Zn—C angles. A few structures with one phenyl group attached to Zn have also been published, e.g. di-µ-phenoxido-bis[(diethyl ether)phenylzinc(II)], which we recently reported (Lennartson & Håkansson, 2008). The dinuclear phenylzinc amide bis[µ2-phenyl-C,C)-{µ2-4,6-bis(dimethylamino)ethylamido}dibenzofuran-N,N',N'',N''']dizinc (Hlavinka & Hagadorn, 2005) is also related to (I), since it has an N-donor ligand rather than the O-donor ligands which appear to be more abundant among the structures previously reported in the CSD.

The molecules in (I) are stacked along c, and molecules of the same chiral sense will fit perfectly on top of each other. There are no unambiguous indications of interactions within these stacks, although there is one intermolecular distance (2.89 Å) within the sum of the van der Waals radii between H8 and C6 (at x, y, 1 + z). Each stack is surrounded by four adjacent stacks, and these stacks appears to be held together by means of edge-to-face ππ-interactions resulting in a network structure (Fig. 3). Each aromatic ring acts both as a donor and as an acceptor. There are two independent sets of interactions in (I), the shortest intermolecular distances being H9···C5 (at 1/2-x, -1/2+y, 2 - z) with a distance of 2.87 Å and H4···C10(1/2 + x, 1/2 - y, 1 - z) with a distance of 2.90 Å. Due to the molecular symmetry, each molecule will be engaged in eight interactions, four of each kind.

Organozinc reagents readily undergo nucleophilic addition to aldehydes and ketones, and the reaction of (I) with a prochiral aldehyde is expected to give rise to a chiral product. If crystallization-induced asymmetric transformation of (I) could be preformed[performed?], it would perhaps be possible to use (I) as a chiral reagent and to obtain an optically active alcohol. This would be similar to the reaction of octahedral `chiral-at-Mg' Grignard reagents with prochiral aldehydes, which give up to 22% enantiomeric excess (Vestergren et al., 2003). Reaction conditions that prevent the reagent from dissolving are required, e.g. a solid-state reaction with an aldehyde. The formation of a solid-state melt could, however, be a potential problem. A problem encountered during crystallization of (I), compared to the Grignard reagents, is a tendency for twinning by inversion. Three crystals from the same crystal batch were picked for absolute structure determination, and two of these crystals were found to be twinned, and almost racemic. Complete spontaneous resolution of (I) would therefore require rigorously controlled crystallization conditions (Gervais et al., 2002; Perez-Garcia & Amabilino, 2002). Determination of an e.e. in a microcrystalline bulk sample of (I) using solid-state CD spectroscopy (Lennartson, Vestergren et al., 2005) would be very difficult due to the high air sensitivity of (I).

Related literature top

For related literature, see: Almenningen et al. (1982); Andersson et al. (1986); Cole et al. (2003); Dickson et al. (2000); Fabicon et al. (1999); Faigl et al. (2008); Feringa & Van Delden (1999); Flack (2003); Gervais et al. (2002); Håkansson et al. (1999); Hlavinka & Hagadorn (2005); Jacques et al. (1981); Johansson & Håkansson (2005); Kondepudi et al. (1990); Kooijman et al. (2007); Lennartson & Håkansson (2008); Lennartson et al. (2005a, 2005b, 2007, 2009); Lewinski et al. (2007); Markies et al. (1990, 1991, 1992); McBride & Carter (1991); Pagni & Compton (2002); Vestergren et al. (2000, 2003).

Experimental top

Bromobenzene (4.1 ml, 0.039 mol) was added to a stirred mixture of magnesium (1.1 g, 0.045 mol) and diethyl ether (40 ml). The mixture was stirred overnight at ambient temperature. The solution was added dropwise to a suspension of zinc chloride (2.6 g, 0.019 mol) in diethyl ether (10 ml) at 273 K. The reaction mixture was stirred at ambient temperature overnight, evaporated and sublimated at 10-2 mbar (1 mbar = 100 Pa). The white product was dissolved in toluene (4 ml). An excess of pyridine (1 ml) was added, whereupon a precipitate formed. The mixture was heated to reflux, and slowly allowed to reach ambient temperature, whereupon colourless crystals of (I) formed.

Refinement top

All H atoms were included in calculated positions and refined using a riding model with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear (Rigaku, 2000); data reduction: CrystalClear (Rigaku, 2000); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick,2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) displaying the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. All H atoms are omitted. The central Zn atom displays a distorted tetrahedral coordination geometry. Symmetry code: (i) 1 - x, 1 - y, z.
[Figure 2] Fig. 2. A molecule of (I) and its mirror image illustrating the conformational chirality of the molecules.
[Figure 3] Fig. 3. The molecules of (I) form stacks along c. The figure shows a stack of four molecules viewed along b.
Diphenyldipyridinezinc(II) top
Crystal data top
[Zn(C6H5)2(C5H5N)2]F(000) = 392
Mr = 377.79Dx = 1.375 Mg m3
Orthorhombic, P21212Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2 2abCell parameters from 5959 reflections
a = 11.931 (2) Åθ = 3.2–25.5°
b = 12.157 (2) ŵ = 1.35 mm1
c = 6.2921 (13) ÅT = 100 K
V = 912.6 (3) Å3Prism, white
Z = 20.4 × 0.3 × 0.2 mm
Data collection top
Rigaku R-AXIS IIC image-plate system
diffractometer
1672 independent reflections
Radiation source: rotating-anode X-ray tube, Rigaku RU-H3R1644 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.022
Detector resolution: 105 pixels mm-1θmax = 25.5°, θmin = 3.2°
ϕ scansh = 1414
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2000)
k = 1414
Tmin = 0.551, Tmax = 0.767l = 77
5959 measured 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)] = 0.017H-atom parameters constrained
wR(F2) = 0.046 w = 1/[σ2(Fo2) + (0.0302P)2 + 0.1732P]
where P = (Fo2 + 2Fc2)/3
S = 1.04(Δ/σ)max < 0.001
1672 reflectionsΔρmax = 0.26 e Å3
124 parametersΔρmin = 0.36 e Å3
0 restraintsAbsolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.061 (10)
Crystal data top
[Zn(C6H5)2(C5H5N)2]V = 912.6 (3) Å3
Mr = 377.79Z = 2
Orthorhombic, P21212Mo Kα radiation
a = 11.931 (2) ŵ = 1.35 mm1
b = 12.157 (2) ÅT = 100 K
c = 6.2921 (13) Å0.4 × 0.3 × 0.2 mm
Data collection top
Rigaku R-AXIS IIC image-plate system
diffractometer
1672 independent reflections
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2000)
1644 reflections with I > 2σ(I)
Tmin = 0.551, Tmax = 0.767Rint = 0.022
5959 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.017H-atom parameters constrained
wR(F2) = 0.046Δρmax = 0.26 e Å3
S = 1.04Δρmin = 0.36 e Å3
1672 reflectionsAbsolute structure: Flack (1983)
124 parametersAbsolute structure parameter: 0.061 (10)
0 restraints
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
C10.35104 (12)0.51973 (12)0.5765 (2)0.0126 (3)
C20.33527 (13)0.60603 (13)0.4290 (3)0.0140 (3)
H20.39150.65850.41420.018 (5)*
C30.23879 (13)0.61611 (12)0.3052 (3)0.0155 (3)
H30.23160.67480.21130.021 (5)*
C40.15420 (13)0.53868 (13)0.3222 (3)0.0154 (3)
H40.09010.54450.23880.017 (5)*
C50.16567 (13)0.45229 (14)0.4649 (3)0.0160 (3)
H50.10940.39970.47660.018 (5)*
C60.26204 (13)0.44414 (13)0.5897 (2)0.0143 (3)
H60.26740.38660.68660.017 (5)*
C70.39766 (13)0.36116 (14)1.0858 (3)0.0150 (3)
H70.35040.42151.10090.021 (5)*
C80.37750 (14)0.26805 (14)1.2085 (3)0.0185 (3)
H80.31790.26631.30380.021 (5)*
C90.44804 (15)0.17815 (14)1.1869 (3)0.0195 (3)
H90.43600.11441.26540.020 (5)*
C100.53713 (14)0.18426 (13)1.0461 (3)0.0177 (3)
H100.58650.12561.03050.018 (5)*
C110.55105 (14)0.27996 (13)0.9284 (2)0.0149 (3)
H110.61040.28360.83290.022 (5)*
N10.48256 (11)0.36714 (10)0.94604 (19)0.0128 (3)
Zn10.50000.50000.72282 (3)0.01101 (8)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0131 (6)0.0153 (9)0.0094 (6)0.0002 (6)0.0018 (5)0.0027 (6)
C20.0143 (7)0.0138 (7)0.0140 (7)0.0032 (6)0.0012 (6)0.0009 (6)
C30.0202 (7)0.0132 (7)0.0129 (7)0.0041 (6)0.0003 (6)0.0006 (6)
C40.0120 (7)0.0197 (7)0.0144 (8)0.0023 (6)0.0025 (6)0.0026 (6)
C50.0123 (7)0.0180 (7)0.0179 (9)0.0041 (6)0.0010 (6)0.0025 (7)
C60.0158 (8)0.0136 (7)0.0136 (8)0.0003 (7)0.0005 (6)0.0017 (6)
C70.0140 (7)0.0176 (8)0.0132 (7)0.0005 (7)0.0001 (6)0.0025 (6)
C80.0189 (7)0.0248 (8)0.0119 (7)0.0067 (7)0.0006 (6)0.0009 (7)
C90.0285 (8)0.0168 (8)0.0131 (8)0.0066 (7)0.0053 (7)0.0020 (6)
C100.0235 (8)0.0127 (7)0.0168 (9)0.0031 (6)0.0060 (6)0.0024 (6)
C110.0156 (7)0.0174 (8)0.0117 (7)0.0019 (7)0.0002 (6)0.0014 (6)
N10.0140 (7)0.0131 (6)0.0112 (5)0.0001 (5)0.0022 (5)0.0006 (4)
Zn10.00980 (12)0.01206 (12)0.01117 (12)0.00009 (11)0.0000.000
Geometric parameters (Å, º) top
C1—C61.407 (2)C7—N11.344 (2)
C1—C21.413 (2)C7—C81.391 (2)
C1—Zn12.0158 (15)C7—H70.9299
C2—C31.395 (2)C8—C91.386 (3)
C2—H20.9300C8—H80.9300
C3—C41.384 (2)C9—C101.386 (2)
C3—H30.9300C9—H90.9300
C4—C51.388 (2)C10—C111.389 (2)
C4—H40.9299C10—H100.9301
C5—C61.396 (2)C11—N11.343 (2)
C5—H50.9301C11—H110.9300
C6—H60.9300N1—Zn12.1505 (12)
C6—C1—C2115.04 (14)C8—C7—H7118.7
C6—C1—Zn1124.11 (11)C9—C8—C7118.82 (16)
C2—C1—Zn1120.37 (11)C9—C8—H8120.6
C3—C2—C1122.80 (14)C7—C8—H8120.6
C3—C2—H2118.6C8—C9—C10119.09 (15)
C1—C2—H2118.6C8—C9—H9120.7
C4—C3—C2119.90 (15)C10—C9—H9120.2
C4—C3—H3120.2C9—C10—C11118.52 (15)
C2—C3—H3119.9C9—C10—H10120.8
C3—C4—C5119.52 (14)C11—C10—H10120.7
C3—C4—H4120.2N1—C11—C10122.97 (15)
C5—C4—H4120.2N1—C11—H11118.7
C4—C5—C6119.91 (15)C10—C11—H11118.4
C4—C5—H5120.0C11—N1—C7118.04 (14)
C6—C5—H5120.1C11—N1—Zn1118.68 (11)
C5—C6—C1122.83 (15)C7—N1—Zn1122.77 (11)
C5—C6—H6118.6C1—Zn1—C1i125.65 (8)
C1—C6—H6118.6C1—Zn1—N1i107.11 (5)
N1—C7—C8122.53 (15)C1—Zn1—N1107.60 (5)
N1—C7—H7118.7N1i—Zn1—N198.45 (7)
Symmetry code: (i) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C9—H9···C5ii0.932.873.765 (2)162
C4—H4···C10iii0.932.903.703 (2)146
Symmetry codes: (ii) x+1/2, y1/2, z+2; (iii) x+1/2, y+1/2, z+1.

Experimental details

Crystal data
Chemical formula[Zn(C6H5)2(C5H5N)2]
Mr377.79
Crystal system, space groupOrthorhombic, P21212
Temperature (K)100
a, b, c (Å)11.931 (2), 12.157 (2), 6.2921 (13)
V3)912.6 (3)
Z2
Radiation typeMo Kα
µ (mm1)1.35
Crystal size (mm)0.4 × 0.3 × 0.2
Data collection
DiffractometerRigaku R-AXIS IIC image-plate system
diffractometer
Absorption correctionMulti-scan
(CrystalClear; Rigaku, 2000)
Tmin, Tmax0.551, 0.767
No. of measured, independent and
observed [I > 2σ(I)] reflections
5959, 1672, 1644
Rint0.022
(sin θ/λ)max1)0.606
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.017, 0.046, 1.04
No. of reflections1672
No. of parameters124
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.26, 0.36
Absolute structureFlack (1983)
Absolute structure parameter0.061 (10)

Computer programs: CrystalClear (Rigaku, 2000), SIR92 (Altomare et al., 1993), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 2009), SHELXL97 (Sheldrick,2008).

Selected geometric parameters (Å, º) top
C1—Zn12.0158 (15)N1—Zn12.1505 (12)
C1—Zn1—C1i125.65 (8)C1—Zn1—N1107.60 (5)
C1—Zn1—N1i107.11 (5)N1i—Zn1—N198.45 (7)
Symmetry code: (i) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C9—H9···C5ii0.9302.8703.765 (2)162.11
C4—H4···C10iii0.9302.8993.703 (2)145.51
Symmetry codes: (ii) x+1/2, y1/2, z+2; (iii) x+1/2, y+1/2, z+1.
 

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