catena-Poly­[[di­bromo­zinc(II)]-di-μ-1,4-dioxan-κ²O:O′]

The title compound, [ZnBr₂(C₄H₈O₂)]_n or ZnBr₂·(dioxan), has a zigzag chain structure in which the 1,4-dioxan mol­ecules link tetrahedrally coordinated Zn atoms. Each dioxan ring sits on a centre of symmetry. The Zn—Br distances are 2.3110 (8) and 2.3169 (8) Å, and angle Br1—Zn1—Br2 is 124.53 (3)°. The Zn—O distances are 2.054 (4) and 2.043 (3) Å, and angle O—Zn—O is 89.6 (15)°.

Comment

1,4-Dioxan forms crystalline adducts with a very wide range of metal halides, nitrates and perchlorates. Phase diagrams of ternary systems (metal halide–dioxan–water) by Lynch and co-workers (e.g. Weicksel & Lynch, 1950; Schott & Lynch, 1966) show that there is competition between water and dioxan at 298 K. Some metals give a hydrate as the only solid product, others give only a dioxan adduct, and a third group form both of these together with ternary compounds.

Structural studies have shown that dioxan may be coordinated directly to a metal or may form hydrogen bonds with the H atoms of coordinated water mol­ecules (e.g. Barnes & Weakley, 1976; Barnes, 2004a). The chair-shaped dioxan mol­ecules cannot chelate. They almost invariably form 1,4-bridges in which each O atom usually coordinates to only one metal atom but may form one or two hydrogen bonds.

ZnCl₂·2(dioxan) (Boardman et al., 1983) has an unusual trigonal pyramidal chain structure which includes a monodentate dioxan. In the present work, we report the structure at 150 K of ZnBr₂·(dioxan), (I).

Fig. 1 shows that (I) consists of zigzag chains, parallel to c, in which dioxan mol­ecules bridge tetrahedrally coordinated zinc atoms. The two independent dioxan mol­ecules lie about the centres of inversion at (½, 0, ½) for O1, C2 and C3, and at (½, 0, 0) for O4, C5 and C6. Selected geometric parameters are given in Table 1. The Zn—Br distances are 2.3110 (8) and 2.3169 (8) Å. These are significantly shorter than those in [ZnBr₂(H₂O)₂]·H₂O.2(1,8-cineol) [2.360 (2) Å, also determined at 120 K (Barnes, 2004b)] and the room-temperature structures of K₂ZnBr₄ (2.405 Å; Fábry et al., 1993) and ZnBr₂·2H₂O (2.483 Å; Duhlev et al., 1988).

The sums of covalent radii are Zn—Br = 2.45 Å and Zn—O = 1.97 Å, while the sums of ionic radii give Zn—Br = 2.78 Å and Zn—O 2.28 Å. These values suggest that the Zn—Br interactions in all these compounds are largely covalent. The Zn—O distances in (I) [2.054 (4) and 2.043 (3) Å] are not significantly different from the Zn—OH₂ distances in [ZnBr₂(H₂O)₂]·H₂O.2(1,8-cineol) and ZnBr₂·2H₂O.

In (I), the torsion angles C3a—C2—O1—Zn1 [155.3 (2)°] and C5b—C6—O4—Zn1 [154.2 (2)°] show that the direction of the O—Zn vectors is close to equatorial rather than the equatorial/axial average often found in dioxan complexes of metal salts (Barnes & Weakley, 1976). Each of the fragments Zn1—O1⋯O1a—Zn1a and Zn1—O4⋯O4b—Zn1b has a torsion angle of 180° [symmetry codes: (a) 1 − x, −y, 1 − z; (b) 1 − x, −y, 2 − z]. The angle between the planes C2/C2a/C3/C3a and C5/C5b/C6/C6b is only 25.2 (4)°. Taken together, these factors produce a very compact zigzag chain structure, which minimizes steric hindrance between the dioxan mol­ecules at the Zn atom. This allows the O—Zn—O angle to be only 89.6 (15)° and so provides space for the unusually close approach of the Br atoms to the zinc, and the large Br1—Zn1—Br2 angle of 124.53 (3)°.

Figure 1 The structure of (I), showing the atom-labelling scheme and 50% probability displacement ellipsoids. [Symmetry codes: (a) 1 − x, −y, 1 − z; (b) 1 − x, −y, 2 − z.]

Experimental

Crystals of (I) were obtained by slow evaporation of a solution of ZnBr₂ in dioxan at room temperature, under an­hydro­us conditions.

Crystal data

• [ZnBr₂(C₄H₈O₂)]

• M_r = 313.29

• Monoclinic, P2₁/n

• a = 7.1326 (2) Å

• b = 12.0376 (4) Å

• c = 9.8312 (3) Å

• β = 99.4200 (14)°

• V = 832.72 (4) ų

• Z = 4

• D_x = 2.499 Mg m⁻³

• Mo Kα radiation

• Cell parameters from 2831 reflections

• θ = 1.9–27.5°

• μ = 12.48 mm⁻¹

• T = 150 (2) K

• Block, colourless

• 0.30 × 0.20 × 0.20 mm

Data collection

• Nonius KappaCCD area-detector diffractometer

• φ and ω cans

• Absorption correction: multi-scan (SORTAV; Blessing, 1995) T_min = 0.052, T_max = 0.083

• 2831 measured reflections

• 1885 independent reflections

• 1606 reflections with I > 2σ(I)

• R_int = 0.031

• θ_max = 27.5°

• h = −9 → 8

• k = −15 → 12

• l = −12 → 12

Refinement

• Refinement on F²

• R[F² > 2σ(F²)] = 0.042

• wR(F²) = 0.106

• S = 1.10

• 1885 reflections

• 83 parameters

• H-atom parameters constrained

• w = 1/[σ²(F_o²) + (0.0512P)² + 3.2775P] where P = (F_o² + 2F_c²)/3

• (Δ/σ)_max < 0.001

• Δρ_max = 1.37 e Å⁻³

• Δρ_min = −0.96 e Å⁻³

• Extinction correction: SHELXL97

• Extinction coefficient: 0.0142 (10)

Table 1
Selected geometric parameters (Å, °)

Zn1—O1	2.043 (3)
Zn1—O4	2.054 (4)
Zn1—Br1	2.3110 (8)
Zn1—Br2	2.3169 (8)

O1—Zn1—O4	89.60 (15)
O1—Zn1—Br1	111.75 (11)
O4—Zn1—Br1	106.06 (10)
O1—Zn1—Br2	107.24 (10)
O4—Zn1—Br2	112.16 (11)
Br1—Zn1—Br2	124.53 (3)
C3—O1—Zn1	117.8 (3)
C2—O1—Zn1	122.1 (3)
C5—O4—Zn1	119.1 (3)
C6—O4—Zn1	121.9 (3)

The H atoms were included in calculated positions and treated as riding atoms; C—H = 0.99 Å and U_iso(H) = 1.3U_eq(parent C atom). The highest peak lies on the Zn1–Br1 vector, 1.11 Å from Zn1.

Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Supporting information

Computing details

Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

catena-Poly[[dibromozinc(II)]-di-µ-1,4-dioxan-κ²O:O']

Crystal data

[ZnBr2(C4H8O2)]	F(000) = 592
Mr = 313.29	Dx = 2.499 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71074 Å
a = 7.1326 (2) Å	Cell parameters from 2831 reflections
b = 12.0376 (4) Å	θ = 1.9–27.5°
c = 9.8312 (3) Å	µ = 12.48 mm^−1
β = 99.4200 (14)°	T = 150 K
V = 832.72 (4) Å^3	Block, colourless
Z = 4	0.30 × 0.20 × 0.20 mm

Data collection

Enraf–Nonius KappaCCD area-detector diffractometer	1885 independent reflections
Radiation source: Enraf–Nonius FR591 rotating anode	1606 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.031
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 2.7°
φ and ω scans to fill Ewald sphere	h = −9→8
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	k = −15→12
Tmin = 0.052, Tmax = 0.083	l = −12→12
2831 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.042	H-atom parameters constrained
wR(F^2) = 0.106	w = 1/[σ^2(Fo^2) + (0.0512P)^2 + 3.2775P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max < 0.001
1885 reflections	Δρmax = 1.37 e Å^−3
83 parameters	Δρmin = −0.96 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0142 (10)

Special details

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.

Hydrogen atoms were placed on calculated positions, riding on the adjacent carbon atom. Isotropic displacement parameters were set at 1.3 times that of the carbon atom.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Zn1	0.34430 (9)	0.17978 (5)	0.73063 (6)	0.0129 (2)
Br1	0.01610 (8)	0.17948 (5)	0.70049 (6)	0.0197 (2)
Br2	0.53024 (8)	0.33850 (4)	0.74508 (6)	0.0195 (2)
O1	0.4446 (5)	0.0740 (3)	0.5968 (4)	0.0151 (8)
C2	0.5349 (8)	0.1139 (4)	0.4840 (5)	0.0157 (11)
H2A	0.6085	0.1822	0.5125	0.020*
H2B	0.4370	0.1322	0.4037	0.020*
C3	0.3348 (8)	−0.0253 (4)	0.5548 (6)	0.0195 (11)
H3A	0.2350	−0.0083	0.4751	0.025*
H3B	0.2721	−0.0519	0.6315	0.025*
O4	0.4332 (5)	0.0709 (3)	0.8889 (4)	0.0162 (8)
C5	0.6330 (8)	0.0636 (5)	0.9438 (6)	0.0201 (12)
H5A	0.6668	0.1205	1.0164	0.026*
H5B	0.7084	0.0781	0.8696	0.026*
C6	0.3207 (8)	0.0493 (5)	0.9969 (5)	0.0176 (11)
H6A	0.1837	0.0536	0.9582	0.023*
H6B	0.3488	0.1061	1.0702	0.023*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0157 (4)	0.0123 (3)	0.0112 (3)	0.0014 (2)	0.0032 (2)	0.0000 (2)
Br1	0.0155 (3)	0.0209 (3)	0.0223 (3)	0.0015 (2)	0.0017 (2)	−0.0004 (2)
Br2	0.0205 (3)	0.0157 (3)	0.0233 (3)	−0.0032 (2)	0.0065 (2)	−0.0037 (2)
O1	0.020 (2)	0.0121 (17)	0.0149 (18)	−0.0021 (15)	0.0093 (16)	−0.0031 (14)
C2	0.027 (3)	0.008 (2)	0.015 (2)	−0.001 (2)	0.010 (2)	0.0021 (19)
C3	0.021 (3)	0.011 (2)	0.028 (3)	−0.006 (2)	0.013 (2)	−0.004 (2)
O4	0.0129 (18)	0.023 (2)	0.0129 (17)	0.0026 (15)	0.0031 (14)	0.0043 (15)
C5	0.013 (3)	0.027 (3)	0.021 (3)	−0.002 (2)	0.003 (2)	0.004 (2)
C6	0.018 (3)	0.023 (3)	0.014 (3)	0.004 (2)	0.008 (2)	0.005 (2)

Geometric parameters (Å, º)

Zn1—O1	2.043 (3)	C3—H3A	0.9900
Zn1—O4	2.054 (4)	C3—H3B	0.9900
Zn1—Br1	2.3110 (8)	O4—C5	1.442 (7)
Zn1—Br2	2.3169 (8)	O4—C6	1.454 (6)
O1—C3	1.451 (6)	C5—C6^ii	1.495 (8)
O1—C2	1.452 (6)	C5—H5A	0.9900
C2—C3^i	1.504 (7)	C5—H5B	0.9900
C2—H2A	0.9900	C6—H6A	0.9900
C2—H2B	0.9900	C6—H6B	0.9900
O1—Zn1—O4	89.60 (15)	O1—C3—H3B	109.8
O1—Zn1—Br1	111.75 (11)	C2^i—C3—H3B	109.8
O4—Zn1—Br1	106.06 (10)	H3A—C3—H3B	108.3
O1—Zn1—Br2	107.24 (10)	C5—O4—C6	110.2 (4)
O4—Zn1—Br2	112.16 (11)	C5—O4—Zn1	119.1 (3)
Br1—Zn1—Br2	124.53 (3)	C6—O4—Zn1	121.9 (3)
C3—O1—C2	110.0 (4)	O4—C5—C6^ii	110.1 (5)
C3—O1—Zn1	117.8 (3)	O4—C5—H5A	109.6
C2—O1—Zn1	122.1 (3)	C6^ii—C5—H5A	109.6
O1—C2—C3^i	109.2 (4)	O4—C5—H5B	109.6
O1—C2—H2A	109.8	C6^ii—C5—H5B	109.6
C3^i—C2—H2A	109.8	H5A—C5—H5B	108.2
O1—C2—H2B	109.8	O4—C6—C5^ii	109.5 (4)
C3^i—C2—H2B	109.8	O4—C6—H6A	109.8
H2A—C2—H2B	108.3	C5^ii—C6—H6A	109.8
O1—C3—C2^i	109.2 (4)	O4—C6—H6B	109.8
O1—C3—H3A	109.8	C5^ii—C6—H6B	109.8
C2^i—C3—H3A	109.8	H6A—C6—H6B	108.2

Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x+1, −y, −z+2.