Lead tartrate from X-ray powder diffraction data

The structure of lead tartrate, Pb²⁺·C₄H₄O₆²⁻, has been solved from X-ray powder diffraction data. The cation exhibits ninefold coordination and the tartrate groups are linked through Pb...O contacts to form a three-dimensional network.

S1. Comment

The structure determination presented in this paper is part of a series of attempts to determine crystal structures from powder diffraction data (e.g. Goubitz et al., 2001; Dova et al., 2001). Crystal structure determination from single-crystal data has become a standard routine during the last decades, provided it is possible to grow suitable crystals. If only a powder is available, then structure determination is certainly by no means a standard procedure. In the last ten years, a number of research groups have attempted to tackle this problem and a couple of program packages now exist [e.g. POWSIM (Jansen et al., 1992a,b, 1993) and SIRPOW (Altomare et al., 1994, 1995)]. These programs apply direct methods to solve the structure.

Recently, Harris et al. (2001) discussed the contemporary advances achieved using Monte Carlo, simulated annealing, grid search and genetic algorithm search methods as the basis of direct-space techniques for powder structure solution. The main problem in structure determination is the number of reflections with reliable intensity that can be extracted from a powder diffractogram. Particularly for lower symmetries (up to orthorhombic) and larger structures, the overlap of reflections often prevents the extraction of reliable intensities, especially at higher θ values. The grid search technique (Chernyshev & Schenk, 1998) used here can overcome this problem for molecules with known conformation. Only the lower angle part of the diffractogram, where overlap of reflections is less severe, is needed to obtain a reliable estimate of the position and orientation of the molecule within the asymmetric unit. Such a solution can be used to refine the structure in a Rietveld refinement procedure.

The title compound, (I), is used as an additive in petroleum to prevent `knocking' or `pinging' in internal combustion engines. It is very toxic and is dangerous for the environment. \sch

Compound (I) turned out to be isomorphous with barium tartrate (González-Silgo et al., 1999). Bond lengths and angles in the tartrate anion of (I) (Table 2) are normal and do not deviate significantly from those of other reported tartrates with divalent cations, i.e. Ca²⁺ (Hawthorne et al., 1982; Ambady, 1968), Mn²⁺ (Ruiz-Pérez et al., 1996), Ni²⁺ (Bostelaar et al., 1984), Zn²⁺ (Templeton et al., 1985), Sr²⁺ (Ambady, 1968) and Ba²⁺ (González-Silgo et al., 1999).

The C1/O1/O2/C2/O3 and C4/O5/O6/C3/O4 planes (Fig. 1) are flat [maximum deviation 0.08 (2) Å for atom C3], and the angle between these planes is 67.6 (6)°, which is close to the value of ~60° usually found in tartrates. The four C atoms assume a typical zigzag planar conformation [C1—C2—C3—C4 - 180 (1)°].

The molecular packing of (I) is shown in Fig. 2. The Pb²⁺ cation is surrounded by six tartrate groups and is linked to nine O atoms (Table 1); the average Pb—O distance is 2.780 (11) Å. In general, the Pb²⁺ cation has a coordination number of eight or ten (see, for example, the overview given by Rogers et al., 1996); a coordination number of nine is also found in [Pb(18-crown-6)(CH₃CN)₃] (von Arnim et al., 1993), in the lead(II) bromide complex with heptaethyleneglycol (Rogers et al., 1996) and in [Pb₉{calix[4]diquinone bis(acid)}₃(ClO₄)₆(OH)₆] (Beer et al., 2000). In the series of reported tartrates with divalent cations, ninefold coordination is also observed for Ba²⁺ (González-Silgo et al., 1999) and eightfold coordination is found for Ca²⁺ (Hawthorne et al., 1982; Ambady, 1968) and Sr²⁺ (Ambady, 1968), whereas Mn²⁺ (Ruiz-Pérez et al., 1996), Ni²⁺ (Bostelaar et al., 1984) and Zn²⁺ (Templeton et al., 1985) are six-coordinated.

S2. Experimental

Lead tartrate was obtained from FLUKA (purity ≥ 98%) and used without further purification.

S3. Refinement

The specimen was mounted in reflection mode (Bragg-Brantano geometry) and spun during measurement. The counting time was 12 s per step. The measurement was performed with a variable divergence slit to irradiate a constant length of 10 mm. The peaks were located with the program PROFIT (Philips, 1996). The orthorhombic cell dimensions were determined using ITO (Visser, 1969) and refined to M₂₀ = 150 and F = 280 using the first 70 peak positions. To obtain reflection intensities, a full-pattern decomposition (FPD) procedure using the program MRIA (Zlokazov & Chernyshev, 1992) was performed; the powder diffraction pattern was fitted employing a split-type pseudo-Voigt peak profile function (Toraya, 1986). The initial molecular model was built from barium L-tartrate from the Cambridge Structural Database (Allen & Kennard, 1993), entry HIXZOD (González-Silgo et al., 1999), replacing Ba with Pb.

To position the molecule in the asymmetric part of the unit cell, the initial model was used in the grid-search procedure (Chernyshev & Schenk, 1998) performed by the program MRIA, using 75 low-angle X_obs values [X_obs and R(X) are defined in expressions (1) and (2) of Chernyshev & Schenk (1998)] extracted from the pattern after the FPD procedure. The model was translated and rotated through the asymmetric unit, with grid increments of ~0.17 Å for molecule translations along a, b and c, and 15° for the three rotations around ϕ, ψ and κ angles, resulting in an R(X) value of 32.8%.

Bond- and angle-restrained Rietveld refinement (RR) was performed with GSAS (Larson & Von Dreele, 1994). The multi-term Simpson's rule integration of the pseudo-Voigt profile function (Howard, 1982) was used and its first 19 coefficients were refined. The preferred orientation was corrected using the spherical-harmonics function implemented in GSAS (Von Dreele, 1997). A cylindrical sample symmetry was chosen and a maximum harmonic order L = 12 was considered. The weight factors (f_d, f_a), weighting the effect of distance and angle restraints on the minimization function, were gradually reduced (from 5000 to 1) in subsequent refinement cycles. During RR, the U_iso values of all atoms were kept fixed at 0.01 Ų. Two powder absorption factors were taken into account for the surface roughness effect, with coefficients A_B1 = 0.38408 and A_B2 = 0.27990 (Suortti, 1972). The X-ray diffraction profile and the difference between the measured and calculated profiles after the RR are shown in Fig. 3.

Computing details

Data collection: Please provide missing information; data reduction: Please provide missing information; program(s) used to solve structure: Please provide missing information; program(s) used to refine structure: GSAS (Larson & Von Dreele, 1994); molecular graphics: Please provide missing information; software used to prepare material for publication: Please provide missing information.

Figures

	Fig. 1. A molecular diagram of the tartrate ligand in (I), showing the atom-numbering scheme.
	Fig. 2. A packing diagram for (I), viewed along the c axis.
	Fig. 3. A Rietveld plot for (I), showing the observed and difference profiles. The reflection positions are shown at the bottom.

Lead tartrate

Crystal data

[Pb(C4H4O6)]	Z = 4
Mr = 355.27	F(000) = 632
Orthorhombic, P212121	Dx = 3.983 Mg m^−3
Hall symbol: p 2ac 2ab	Cu Kα radiation, λ = 1.54056 Å
a = 7.99482 (3) Å	T = 295 K
b = 8.84525 (4) Å	white
c = 8.35318 (4) Å	flat sheet, 20 × 0.05 mm
V = 590.71 (1) Å^3

Data collection

XPERT PRO Alpha-1 diffractometer	Data collection mode: reflection
Radiation source: sealed X-ray tube, line	Scan method: continuous
Johannson monochromator	2θmin = 12.438°, 2θmax = 74.933°, 2θstep = 0.005°
Specimen mounting: sprinkled as a thin layer on the specimen holder

Refinement

Least-squares matrix: full	43 parameters
Rp = 0.114	31 restraints
Rwp = 0.152	H atoms treated by a mixture of independent and constrained refinement
Rexp = 0.091	Weighting scheme based on measured s.u.'s
R(F^2) = 0.105	(Δ/σ)max = 0.13
χ^2 = 2.856	Background function: GSAS Background function number 1 with 9 terms. Shifted Chebyshev function of 1st kind 1: 23.2328 2: 15.3492 3: -1.86066 4: -2.10346 5: -1.16661 6: -1.42882 7: -1.76251 8: -0.653488 9: -0.646831
13800 data points	Preferred orientation correction: Spherical Harmonic ODF Spherical harmonic order= 12 The sample symmetry is: cylindrical (fiber texture) Index = 2 0 0 Coeff= -0.1155 Index = 2 0 2 Coeff= 0.0946 Index = 4 0 0 Coeff= 0.1865 Index = 4 0 2 Coeff= 0.1985 Index = 4 0 4 Coeff= -0.1922 Index = 6 0 0 Coeff= -0.6389 Index = 6 0 2 Coeff= -0.3721 Index = 6 0 4 Coeff= -0.0609 Index = 6 0 6 Coeff= -0.7518 Index = 8 0 0 Coeff= 0.2137 Index = 8 0 2 Coeff= -0.1717 Index = 8 0 4 Coeff= -0.3871 Index = 8 0 6 Coeff= 0.1447 Index = 8 0 8 Coeff= 0.3167 Index = 10 0 0 Coeff= -0.3410 Index = 10 0 2 Coeff= 0.2917 Index = 10 0 4 Coeff= -0.8413 Index = 10 0 6 Coeff= -1.1218 Index = 10 0 8 Coeff= 0.3545 Index = 10 0 10 Coeff= 1.0021 Index = 12 0 0 Coeff= 1.4161 Index = 12 0 2 Coeff= -0.8332 Index = 12 0 4 Coeff= 0.3133 Index = 12 0 6 Coeff= -1.0567 Index = 12 0 8 Coeff= 0.7183 Index = 12 0 10 Coeff= 0.0528 Index = 12 0 12 Coeff= 1.1920 Prefered orientation correction range: Min= 0.58210, Max= 1.67259
Profile function: CW Profile function number 3 with 19 terms Pseudovoigt profile coefficients as parameterized in P. Thompson, D.E. Cox & J.B. Hastings (1987). J. Appl. Cryst.,20,79-83. Asymmetry correction of L.W. Finger, D.E. Cox & A. P. Jephcoat (1994). J. Appl. Cryst.,27,892-900. #1(GU) = 3.797 #2(GV) = 10.806 #3(GW) = -1.506 #4(GP) = 2.259 #5(LX) = 0.000 #6(LY) = 0.000 #7(S/L) = 0.0000 #8(H/L) = 0.0000 #9(trns) = 0.00 #10(shft)= 0.0000 #11(stec)= 0.00 #12(ptec)= 0.00 #13(sfec)= 0.00 #14(L11) = 0.000 #15(L22) = 0.000 #16(L33) = 0.000 #17(L12) = 0.000 #18(L13) = 0.000 #19(L23) = 0.000 Peak tails are ignored where the intensity is below 0.0010 times the peak Aniso. broadening axis 0.0 0.0 1.0

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

	x	y	z	Uiso*/Ueq
O1	−0.0771 (15)	0.0988 (13)	0.1293 (14)	0.01*
O2	0.1070 (14)	0.1712 (14)	−0.0063 (14)	0.01*
O3	0.1588 (11)	−0.007 (2)	0.3594 (10)	0.01*
H3O	0.22898	−0.02231	0.41589	0.01*
O4	0.2189 (14)	0.3176 (13)	0.2999 (14)	0.01*
H4O	0.14152	0.26983	0.36637	0.01*
O5	0.5808 (13)	0.0761 (12)	0.3292 (14)	0.01*
O6	0.4835 (14)	0.2460 (13)	0.4925 (14)	0.01*
C1	0.0809 (17)	0.105 (2)	0.1171 (19)	0.01*
C2	0.2161 (15)	0.0544 (13)	0.2153 (16)	0.01*
H2	0.28328	−0.02695	0.14311	0.01*
C3	0.3282 (18)	0.1926 (16)	0.2515 (14)	0.01*
H3	0.36818	0.22372	0.14406	0.01*
C4	0.480 (2)	0.1875 (18)	0.3470 (18)	0.01*
Pb	−0.34155 (8)	0.0007 (3)	−0.05454 (9)	0.01*

Geometric parameters (Å, º)

Pb—O1	2.754 (12)	H4O—O4	0.932
Pb—O1^i	2.859 (12)	O5—O6	2.173 (16)
Pb—O2^ii	2.975 (13)	O5—C4	1.280 (12)
Pb—O3^i	2.637 (9)	O5—Pb^vii	2.398 (11)
Pb—O4^ii	2.649 (11)	O6—O5	2.173 (16)
Pb—O4^iii	2.847 (12)	O6—C4	1.321 (12)
Pb—O5^iv	2.398 (11)	O6—Pb^viii	2.575 (12)
Pb—O6^iii	2.575 (12)	C1—O1	1.268 (12)
O1—O2	1.964 (16)	C1—O2	1.204 (12)
O1—C1	1.268 (12)	C1—C2	1.429 (12)
O1—Pb	2.754 (12)	C2—O3	1.399 (15)
O1—Pb^v	2.859 (12)	C2—C1	1.429 (12)
O2—O1	1.964 (16)	C2—H2	1.082
O2—C1	1.204 (12)	C2—C3	1.545 (12)
O2—Pb^vi	2.975 (13)	H2—C2	1.082
O3—H3O	0.745	C3—O4	1.466 (17)
O3—C2	1.399 (15)	C3—C2	1.545 (12)
O3—Pb^v	2.637 (9)	C3—H3	0.991
H3O—O3	0.745	C3—C4	1.455 (13)
H3O—H2^vii	1.9498	H3—C3	0.991
O4—H4O	0.932	C4—O5	1.280 (12)
O4—C3	1.466 (17)	C4—O6	1.321 (12)
O4—Pb^vi	2.649 (11)	C4—C3	1.455 (13)
O4—Pb^viii	2.847 (12)
H3O—O3—C2	111.6	H2—C2—C3	110.3
H3O—O3—Pb^v	123.7	O4—C3—C2	107.8 (10)
C2—O3—Pb^v	122.7 (8)	O4—C3—H3	103.5
H4O—O4—C3	102.6	O4—C3—C4	111.7 (11)
C4—O5—Pb^vii	135.8 (10)	C2—C3—H3	103.3
C4—O6—Pb^viii	121.3 (9)	C2—C3—C4	124.5 (13)
O1—C1—O2	105.2 (13)	H3—C3—C4	103.6
O1—C1—C2	134.0 (13)	O5—C4—O6	113.3 (13)
O2—C1—C2	120.8 (13)	O5—C4—C3	119.0 (13)
O3—C2—C1	111.6 (10)	O6—C4—C3	120.5 (12)
O3—C2—H2	112.5	O3^i—Pb—O5^iv	137.1 (4)
O3—C2—C3	109.3 (11)	O3^i—Pb—O6^iii	69.6 (5)
C1—C2—H2	105.2	O5^iv—Pb—O6^iii	102.5 (4)
C1—C2—C3	107.7 (12)

Symmetry codes: (i) −x−1/2, −y, z−1/2; (ii) x−1/2, −y+1/2, −z; (iii) −x, y−1/2, −z+1/2; (iv) −x+1/2, −y, z−1/2; (v) −x−1/2, −y, z+1/2; (vi) x+1/2, −y+1/2, −z; (vii) −x+1/2, −y, z+1/2; (viii) −x, y+1/2, −z+1/2.