Dichlorobis(2-methylquinoline N-oxide-[kappa]O)zinc(II) from powder data

The crystal structure of the title compound, [ZnCl₂(C₁₀H₉NO)₂], has been determined from laboratory powder diffraction data. Although the powder pattern was initially indexed with tetragonal unit-cell dimensions, the correct solution was found in an orthorhombic space group using a combination of grid-search and simulated-annealing techniques. The subsequent bond-restrained Rietveld refinement gave bond lengths and angles within expected ranges. The molecule has crystallographically imposed twofold symmetry.

S1. Comment

Heteroatomic N-oxides, and their complexes and salts demonstrate a broad spectrum of biological activity. Some are used as medical remedies (Albini & Pietra, 1991) or plant growth activators (Ponomarenko, 1999). N-oxidation is one of the detoxification pathways of heterocycles in living things (Murray et al., 1997; Hecht, 1996). The necessity of establishing structure-property relationships for this class of compounds led to the crystal structure determination of the title compound, (I). \sch

In the crystal structure of (I), the Zn atom is situated on a twofold axis (Fig. 1). Selected geometric parameters are given in Table 1. The coordination polyhedron of the Zn atom is a slightly distorted tetrahedron, with edge lengths of Cl1—Cl1ⁱ 3.885 (6), O1—O1ⁱ 3.20 (2), Cl1—O1 3.41 (1) and Cl1—O1ⁱ 3.38 (1) Å [symmetry code: (i) -x, y, 1/2 - z]. Is this the correct symmetry code? The distortions of the Zn tetrahedron in (I) are less than those in dichlorobis(2,6-lutidine N-oxide)zinc(II) (Sager & Watson, 1968) and dichlorobis(pyridine N-oxide-O)zinc(II) (McConnell et al., 1986). The molecules of (I) form bent chains stretching along the a axis. The distance between Zn atoms in the chain is 9.95 Å.

Although the unit-cell dimensions seemed to be tetragonal, the crystal structure solution of (I) from powder data turned out not to be an easy task. The measured powder patterns admitted a long list of possible space groups. Therefore, various space groups (first, tetragonal, such as P4₂2₁2 (94), P4₂/m (84), P4₂ (77) and some others, and then orthorhombic) were tested while also using grid-search (Chernyshev & Schenk, 1998) and simulated annealing (Zhukov et al., 2001) techniques to solve the crystal structure of (I). The solution was found in the orthorhombic space group Pna2₁ (33) and transformed with the ADDSYM option of PLATON (Spek, 2000) into Pbcn (60).

S2. Experimental

2-Methylquinoline N-oxide was synthesized according to the procedure of Ochiai (1953). Compound (I) was prepared in polycrystalline form by mixing warm saturated 2-methylquinoline N-oxide and zinc chloride solutions in ethanol in molar ratio, and subsequent washing with ethanol and diethyl ether of the precipitate obtained (yield 60%). IR spectra were measured in KBr using a Specord M-40 spectrometer. The intensities of the N—O bands (1340 and 1272 cm^-1) decreased in (I) in comparison with the spectrum of the parent N-oxide. Bands at 1188 cm^-1 (induced by connection of zinc chloride to the N—O group) and 328–305 cm^-1 (Zn—Cl bonds) (Whyman et al., 1967; Garvey et al., 1968) are also present.

S3. Refinement

Two X-ray powder diffraction patterns were measured in reflection mode on an XPert PRO X-ray powder diffraction system equipped with a standard PW 3050/60 resolution goniometer and PW 3011/20 proportional point detector. The first pattern, measured in the range 2–40° with the narrowest beam attenuator, was used for indexing, while the second was used for structure solution and refinement. The powder was sprinkled on the sample holder using a small sieve to avoid a preferred orientation. The thickness of the sample was no more than 0.1 mm. During the exposures, the specimen was spun in its plane to improve particle statistics. The unit-cell dimensions were determined with the indexing program TREOR (Werner et al., 1985), and were refined in tetragonal space groups with the program LSPAID (Visser, 1986) to M₂₀ = 47 and F₃₀ = 85 (0.006, 61) using the first 30 peak positions. However, several of the tested tetragonal space groups could not provide an appropriate solution. A correct solution was found in the orthorhombic space group Pna2₁ (33) in a two-step procedure. First, the rigid ZnCl₂O₂ fragment was located in the asymmetric part of the unit cell using the grid-search procedure (Chernyshev & Schenk, 1998), using a set of 250 high-angle X_obs values extracted from the pattern by the full pattern decomposition procedure. Second, the orientations of the two 2-methylquinoline N-oxide fragments were found with the simulated annealing technique (Zhukov et al., 2001), using a set of 70 low-angle X_obs values. Preliminary bond-restrained Rietveld refinement showed the presence of local symmetry, axis 2. The crystal structure obtained at this stage was tested with the ADDSYM option of PLATON (Spek, 2000) and transformed into space group Pbcn (60). The final bond-restrained Rietveld refinement was performed in the correct space group, Pbcn. The strength of the restraints was a function of interatomic separation and, for intramolecular bond lengths, corresponds to an r.m.s. deviation of 0.03 Å. An additional restraint was applied to the planarity of the 2-methylquinoline N-oxide fragment. Three isotropic atomic displacement parameters were refined: two for Zn and Cl1, and the overall U_iso parameter for the rest of non-H atoms. H atoms were placed in geometrically calculated positions and allowed to refine using bond restraints, with a common isotropic displacement parameter U_iso(H) fixed to 0.05 Ų. The diffraction profiles and the differences between the measured and calculated profiles are shown on Fig. 2.

Computing details

Data collection: local program; cell refinement: LSPAID (Visser, 1986); data reduction: local program; program(s) used to solve structure: MRIA (Zlokazov & Chernyshev, 1992); program(s) used to refine structure: MRIA; molecular graphics: PLATON (Spek, 2000); software used to prepare material for publication: MRIA, SHELXL97 (Sheldrick, 1997) and PARST (Nardelli, 1983).

Figures

	Fig. 1. The molecular structure of (I) with the atomic numbering.
	Fig. 2. The Rietveld plot, showing the observed and difference profiles for (I). The reflection positions are shown above the difference profile.

Dichlorobis(2-methylquinoline N-oxide-κO)zinc(II)

Crystal data

[ZnCl2(C10H9NO)2]	F(000) = 928
Mr = 454.63	Dx = 1.501 Mg m^−3
Orthorhombic, Pbcn	Melting point: 493(1) K
Hall symbol: -P 2n 2ab	Cu Kα1 radiation, λ = 1.54056 Å
a = 14.052 (6) Å	T = 293 K
b = 10.192 (5) Å	Particle morphology: no specific habit
c = 14.047 (6) Å	light grey
V = 2011.8 (16) Å^3	flat_sheet, 20 × 20 mm
Z = 4

Data collection

XPert PRO X-ray diffraction system diffractometer	Data collection mode: reflection
Radiation source: PW3373/00, line-focus sealed tube	Scan method: step
PW3110/65, four Ge(220) crystals monochromator	2θmin = 10°, 2θmax = 70°, 2θstep = 0.01°
Specimen mounting: The powder was sprinkled on the sample holder using a small sieve. The thickness of the layer was no more than 0.1 mm.

Refinement

Refinement on Inet	64 parameters
Least-squares matrix: full with fixed elements per cycle	74 restraints
Rp = 0.083	1 constraint
Rwp = 0.114	H-atom parameters constrained
Rexp = 0.086	Weighting scheme based on measured s.u.'s
χ^2 = 1.742	(Δ/σ)max = 0.01
6001 data points	Background function: Chebyshev polynomial up to the 5th order
Profile function: split-type pseudo-Voigt (Toraya, 1986)	Preferred orientation correction: none

Special details

Experimental. specimen was rotated in its plane

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.

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

	x	y	z	Uiso*/Ueq
Zn	0.0000	0.2186 (3)	0.2500	0.060 (1)*
Cl1	−0.1368 (3)	0.3277 (4)	0.2700 (3)	0.064 (2)*
O1	−0.0144 (6)	0.1043 (8)	0.1370 (6)	0.049 (1)*
N1	0.0601 (10)	0.1072 (13)	0.0775 (8)	0.049*
C2	0.1317 (11)	0.0199 (13)	0.0905 (11)	0.049*
C3	0.2118 (9)	0.0180 (14)	0.0273 (11)	0.049*
C4	0.2171 (10)	0.0999 (15)	−0.0489 (10)	0.049*
C5	0.1496 (11)	0.2879 (14)	−0.1372 (12)	0.049*
C6	0.0764 (12)	0.3752 (14)	−0.1497 (9)	0.049*
C7	−0.0011 (12)	0.3774 (13)	−0.0885 (10)	0.049*
C8	−0.0106 (12)	0.2866 (14)	−0.0164 (8)	0.049*
C9	0.0645 (11)	0.1963 (15)	−0.0012 (9)	0.049*
C10	0.1450 (11)	0.1957 (13)	−0.0622 (10)	0.049*
C11	0.1271 (10)	−0.0802 (14)	0.1690 (10)	0.049*
H3	0.2592	−0.0439	0.0362	0.051*
H4	0.2704	0.0983	−0.0884	0.051*
H5	0.1998	0.2849	−0.1803	0.051*
H6	0.0785	0.4336	−0.2013	0.051*
H7	−0.0510	0.4354	−0.0998	0.051*
H8	−0.0625	0.2895	0.0243	0.051*
H111	0.0741	−0.0638	0.2076	0.051*
H112	0.1234	−0.1656	0.1398	0.051*
H113	0.1854	−0.0751	0.2048	0.051*

Geometric parameters (Å, º)

Zn—Cl1^i	2.238 (5)	C5—H5	0.93
Zn—O1^i	1.979 (9)	C6—C7	1.39 (2)
Zn—Cl1	2.238 (5)	C6—H6	0.94
Zn—O1	1.979 (9)	C7—C8	1.38 (2)
O1—N1	1.341 (16)	C7—H7	0.93
N1—C9	1.432 (18)	C8—H8	0.93
C2—N1	1.35 (2)	C9—C8	1.42 (2)
C2—C11	1.50 (2)	C9—C10	1.42 (2)
C3—C4	1.36 (2)	C10—C5	1.41 (2)
C3—C2	1.43 (2)	C10—C4	1.42 (2)
C3—H3	0.93	C11—H111	0.94
C4—H4	0.93	C11—H112	0.96
C5—C6	1.37 (2)	C11—H113	0.96
O1—Zn—O1^i	107.9 (6)	C3—C4—C10	119 (1)
O1—Zn—Cl1^i	106.2 (3)	C3—C4—H4	120
O1^i—Zn—Cl1^i	107.8 (3)	C10—C4—H4	121
O1—Zn—Cl1	107.8 (3)	C6—C5—C10	120 (1)
O1^i—Zn—Cl1	106.2 (3)	C6—C5—H5	121
Cl1^i—Zn—Cl1	120.4 (2)	C10—C5—H5	120
N1—O1—Zn	114.0 (7)	C5—C6—C7	121 (1)
C4—C3—C2	121 (1)	C5—C6—H6	119
C4—C3—H3	119	C7—C6—H6	120
C2—C3—H3	119	C8—C7—C6	121 (1)
N1—C2—C3	121 (1)	C8—C7—H7	119
N1—C2—C11	121 (1)	C6—C7—H7	120
C3—C2—C11	119 (1)	C7—C8—C9	118 (1)
O1—N1—C2	119 (1)	C7—C8—H8	121
O1—N1—C9	122 (1)	C9—C8—H8	121
C2—N1—C9	119 (1)	C2—C11—H111	110
C8—C9—C10	120 (1)	C2—C11—H112	108
C8—C9—N1	120 (1)	H111—C11—H112	111
C10—C9—N1	120 (1)	C2—C11—H113	108
C5—C10—C9	119 (1)	H111—C11—H113	111
C5—C10—C4	122 (1)	H112—C11—H113	109
C9—C10—C4	120 (1)
Cl1—Zn—O1—N1	135.0 (8)	Zn—O1—N1—C2	90 (1)

Symmetry code: (i) −x, y, −z+1/2.