Crystal structure of lead(II) tartrate: a redetermination

Weil, M.

doi:10.1107/S2056989014027376

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Volume 71| Part 1| January 2015| Pages 82-84

https://doi.org/10.1107/S2056989014027376

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Crystal structure of lead(II) tartrate: a redetermination

Matthias Weil ^a ^*

^aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
^*Correspondence e-mail: mweil@mail.zserv.tuwien.ac.at

Edited by H. Stoeckli-Evans, University of Neuchâtel, Switzerland (Received 10 December 2014; accepted 15 December 2014; online 1 January 2015)

Single crystals of poly[μ₄-tartrato-κ⁶O¹,O³:O^1′:O²,O⁴:O^4′-lead], [Pb(C₄H₄O₆)]_n, were grown in a gel medium. In comparison with the previous structure determination of this compound from laboratory powder X-ray diffraction data [De Ridder et al. (2002 ). Acta Cryst. C58, m596–m598], the redetermination on the basis of single-crystal data reveals the absolute structure, all atoms with anisotropic displacement parameters and a much higher accuracy in terms of bond lengths and angles. It could be shown that a different space group or incorporation of water as reported for similarly gel-grown lead tartrate crystals is incorrect. In the structure, each Pb²⁺ cation is bonded to eight O atoms of five tartrate anions, while each tartrate anion links four Pb²⁺ cations. The resulting three-dimensional framework is stabilized by O—H⋯O hydrogen bonds between the OH groups of one tartrate anion and the carboxylate O atoms of adjacent anions.

Keywords: crystal structure; lead tartrate; gel growth; redetermination; O—H⋯O hydrogen bonds.

CCDC reference: 1039408

1. Chemical context

Crystal growth in gels (Henisch, 1970 ) is a convenient method to obtain single crystals of high quality from compounds with rather low solubility products. Therefore gel growth was the method of choice for single-crystal growth of the low-soluble fluorophosphate BaPO₃F. This compound is interesting insofar as the polycrystalline material (prepared by fast precipitation) has orthorhombic symmetry whereas single crystals grown slowly in a gel have monoclinic symmetry. Both the orthorhombic and monoclinic BaPO₃F phases belong to the same order–disorder (OD) family and can be derived from the baryte (BaSO₄) structure type by replacing the SO₄²⁻ anions with isoelectronic PO₃F²⁻ anions in two orientations (Stöger et al., 2013 ). The same baryte-type structure has been reported for PbPO₃F on the basis of similar lattice parameters and systematic absences of reflections (Walford, 1967 ). However, structural details were not determined at that time. In analogy with the barium compound, it was intended to grow crystals of lead fluorophosphate in a gel medium. In order to take into account the somewhat lower solubility of PbPO₃F in comparison with BaPO₃F (Lange, 1929 ), crystal-growth experiments were performed with lead salts in ammoniacal tartrate solutions to produce a soluble, poorly dissociated lead tartrate complex which lowers the concentration of Pb²⁺ to such an extent that its direct precipitation is prevented. In fact, after some days colourless single crystals appeared in the gel medium that, on the basis of unit-cell determinations, turned out to be lead tartrate, [Pb(C₄H₄O₆)]. The structure of this compound was originally solved and refined from laboratory X-ray powder diffraction data in space group P2₁2₁2₁ (De Ridder et al., 2002). However, some years later it was reported that gel-grown lead tartrate crystallizes as a dihydrate (Lillybai & Rahimkutty, 2010 ) or in a different space group (Pna2₁; Labutina et al., 2011 ). Motivated by these disagreements, it was decided to re-investigate the crystal structure of gel-grown lead tartrate on the basis of single-crystal diffraction data for an unambiguous determination of the space group and the composition, and to obtain more precise results compared to the powder refinement.

2. Structural commentary

The present study confirms in principle the results of the previous powder X-ray diffraction study and reveals the determination of the absolute structure (Flack parameter 0.003 (7); Flack, 1983 ) and all non-H atoms refined with anisotropic displacement parameters. In comparison with the powder study, the higher precision and accuracy of the present model is, for example, reflected by the notable differences in the Pb—O bond lengths determined in the two studies (Table 1). An important result of the present study is that neither a different space group nor a different content in terms of an incorporation of water into the structure could be found on the basis of the single-crystal data.

Table 1
Comparison of the Pb—O bond lengths (Å) in the current and the previous (De Ridder et al., 2002) refinements of lead tartrate

For the previous refinement: a = 7.99482 (3), b = 8.84525 (4), c = 8.35318 (4) Å.

Bond	current refinement	previous refinement
Pb—O1ⁱ	2.472 (2)	2.859 (12)
Pb—O5ⁱⁱ	2.482 (2)	2.398 (11)
Pb—O6ⁱⁱⁱ	2.594 (2)	2.575 (12)
Pb—O3ⁱ	2.5972 (17)	2.637 (9)
Pb—O4^iv	2.6878 (19)	2.649 (11)
Pb—O4ⁱⁱⁱ	2.7866 (19)	2.847 (12)
Pb—O2^iv	2.935 (2)	2.975 (13)
Pb—O1	3.004 (2)	2.754 (12)
Symmetry codes: (i) −x − $[{1\over 2}]$ , −y, z − $[{1\over 2}]$ ; (ii) −x + $[{1\over 2}]$ , −y, z − $[{1\over 2}]$ ; (iii) −x, y − $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (iv) x − $[{1\over 2}]$ , −y + $[{1\over 2}]$ , −z.

The Pb²⁺ cation has a coordination number of eight considering a cut-off value of 3 Å for the ligating oxygen atoms. The coordination polyhedron is considerably distorted (Fig. 1), with Pb—O distances in the range 2.472 (2)–3.004 (2) Å (Table 1). The resulting bond-valence sum (Brown, 2002 ) of 1.75 valence units, using the parameters of Krivovichev & Brown (2001 ) for the Pb—O bonds, is reasonably close to the expected value of 2.0 valence units. Bond lengths and angles within the tartrate anion are in normal ranges.

Figure 1
Coordination environment of the Pb²⁺ cation in the title compound, with atom labelling (for symmetry codes refer to Table 1

). Displacement ellipsoids are drawn at the 50% probability level.

3. Packing features

In the crystal structure, the Pb²⁺ cations are arranged in hexagonally packed rows extending parallel to [100] (Fig. 2). Each Pb²⁺ cation is bonded to five tartrate anions (three chelating and two in a monodentate fashion, Fig. 1) while each tartrate anion links four Pb²⁺ cations, leading to a three-dimensional framework. O—H⋯O hydrogen bonds (Table 2) between the hydroxy groups of one tartrate anion and the carboxylate O atoms of adjacent tartrate anions stabilize this arrangement. Since no solvent-accessible voids were observed in the crystal structure, an incorporation of water molecules as reported by Lillibay & Rahimkutty (2010) is impossible.

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3O⋯O2ⁱ	0.84 (1)	2.02 (4)	2.646 (3)	131 (5)
O4—H4O⋯O6ⁱⁱ	0.85 (1)	1.79 (1)	2.618 (3)	169 (4)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, -y, z+{\script{1\over 2}}]$ ; (ii) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ .

Figure 2
The crystal packing of the title compound in projection along [ $[\overline{1}]$ 00]. Only complete tartrate anions are shown. O—H⋯O hydrogen bonds are shown in blue (see Table 2

for details). Pb—O bonds have been omitted for clarity. Colour code: Pb green, C grey, O red, H white.

4. Database survey

Tartaric acid and its salts or coordination compounds have been structurally examined in great detail. The current release of the CSD (Version 5.35 with all updates; Groom & Allen, 2014 ) revealed 644 entries, including the pure acid, co-crystals, compounds with the hydrogen tartrate anion and compounds with the tartrate anion.

5. Synthesis and crystallization

Commercially available gelatin was dissolved in hot water. The solution (50 ml) was cooled to about 300 K and 300 mg of (NH₄)₂(PO₃F)(H₂O), prepared according to Schülke & Kayser (1991 ), were dissolved in the still liquid solution that was filled in a large test tube. After initiation of gelling, a second neutral gel layer was put on top of the first gel layer. After the neutral gel had set, an aqueous solution consisting of Pb(NO₃)₂ (30 mg) and sodium potassium tartrate (250 mg) was poured over the second gel layer. After three weeks, colourless single crystals of lead(II) tartrate, mostly with a block-like form, could be isolated. PbPO₃F in the form of polycrystalline material was also present in the reaction mixture as revealed by powder X-ray diffraction measurements.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. Atom labelling and starting coordinates for the refinement were taken from the previous powder diffraction study (De Ridder et al., 2002). H atoms bonded to C atoms were placed in calculated positions and refined as riding atoms, with C—H = 0.98 Å and with U_iso(H) = 1.2U_eq(C). Hydroxyl H atoms were found from difference Fourier maps and refined with an O—H distance restraint of 0.85 (1) Å and with U_iso(H) = 1.2U_eq(O). The highest and lowest remaining electron densities are found 0.59 and 0.49 Å, respectively, from the Pb atom and are caused by truncation effects. No other electron densities attributable to additional atoms could be found, ruling out an incorporation of water molecules. Refinements in space group Pna2₁ as suggested by Labutina et al. (2011) led to unreasonable models.

Table 3
Experimental details

Crystal data
Chemical formula	[Pb(C₄H₄O₆)]
M_r	355.26
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	296
a, b, c (Å)	7.9890 (2), 8.8411 (3), 8.3434 (2)
V (Å³)	589.31 (3)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	28.61
Crystal size (mm)	0.15 × 0.15 × 0.09

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2013 )
T_min, T_max	0.099, 0.183
No. of measured, independent and observed [I > 2σ(I)] reflections	81742, 4512, 3836
R_int	0.046
(sin θ/λ)_max (Å⁻¹)	0.971

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.021, 0.042, 1.06
No. of reflections	4512
No. of parameters	108
No. of restraints	2
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	3.20, −2.26
Absolute structure	Flack (1983), 1959 Friedel pairs
Absolute structure parameter	−0.003 (7)
Computer programs: APEX2 and SAINT-Plus (Bruker, 2013), SHELXS97 and SHELXL97 (Sheldrick, 2008 ), ATOMS (Dowty, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1039408

Crystal structure: contains datablocks I, general. DOI: https://doi.org/10.1107/S2056989014027376/su5041sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989014027376/su5041Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT-Plus (Bruker, 2013); data reduction: SAINT-Plus (Bruker, 2013); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Poly[µ₄-tartrato-κ⁶O¹,O³:O^1':O²,O⁴:O^4'-lead] top

Crystal data top

[Pb(C₄H₄O₆)]	F(000) = 632
M_r = 355.26	D_x = 4.004 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 9854 reflections
a = 7.9890 (2) Å	θ = 3.4–40.9°
b = 8.8411 (3) Å	µ = 28.61 mm⁻¹
c = 8.3434 (2) Å	T = 296 K
V = 589.31 (3) Å³	Block, colourless
Z = 4	0.15 × 0.15 × 0.09 mm

Data collection top

Bruker APEXII CCD diffractometer	4512 independent reflections
Radiation source: fine-focus sealed tube	3836 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.046
ω– and φ–scans	θ_max = 43.7°, θ_min = 3.4°
Absorption correction: multi-scan (SADABS; Bruker, 2013)	h = −15→15
T_min = 0.099, T_max = 0.183	k = −17→17
81742 measured reflections	l = −16→16

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.021	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.042	w = 1/[σ²(F_o²) + (0.0155P)² + 1.1508P] where P = (F_o² + 2F_c²)/3
S = 1.06	(Δ/σ)_max = 0.007
4512 reflections	Δρ_max = 3.20 e Å⁻³
108 parameters	Δρ_min = −2.26 e Å⁻³
2 restraints	Absolute structure: Flack (1983), 1959 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.003 (7)

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

	x	y	z	U_iso*/U_eq
Pb1	−0.342448 (9)	0.001349 (17)	−0.054104 (9)	0.01396 (2)
O1	−0.0806 (2)	0.1027 (2)	0.1809 (3)	0.0159 (3)
O2	0.1001 (3)	0.1758 (3)	−0.0066 (2)	0.0180 (4)
O3	0.1564 (2)	−0.0126 (3)	0.3659 (2)	0.0147 (3)
O4	0.2220 (2)	0.3195 (2)	0.3069 (2)	0.0123 (3)
O5	0.5788 (3)	0.0785 (3)	0.3132 (3)	0.0215 (4)
O6	0.4746 (3)	0.2388 (3)	0.4968 (3)	0.0244 (5)
C1	0.0635 (3)	0.1138 (3)	0.1249 (3)	0.0103 (3)
C2	0.2130 (3)	0.0566 (3)	0.2235 (3)	0.0100 (3)
H2	0.2764	−0.0171	0.1601	0.012*
C3	0.3222 (3)	0.1966 (3)	0.2538 (3)	0.0101 (3)
H3	0.3686	0.2263	0.1497	0.012*
C4	0.4706 (3)	0.1686 (3)	0.3642 (3)	0.0128 (4)
H3O	0.224 (4)	−0.019 (6)	0.443 (4)	0.029 (12)*
H4O	0.144 (4)	0.288 (5)	0.367 (4)	0.015 (10)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Pb1	0.01063 (3)	0.01446 (3)	0.01679 (3)	0.00067 (7)	−0.00006 (2)	0.00120 (7)
O1	0.0081 (6)	0.0230 (9)	0.0167 (8)	0.0000 (6)	−0.0005 (6)	0.0032 (7)
O2	0.0155 (8)	0.0274 (10)	0.0111 (7)	0.0026 (8)	−0.0009 (6)	0.0057 (7)
O3	0.0116 (5)	0.0192 (9)	0.0134 (6)	0.0001 (8)	0.0009 (5)	0.0072 (7)
O4	0.0092 (6)	0.0113 (7)	0.0165 (8)	0.0011 (5)	0.0001 (6)	0.0004 (6)
O5	0.0100 (7)	0.0277 (11)	0.0267 (11)	0.0073 (7)	−0.0009 (7)	−0.0005 (8)
O6	0.0252 (10)	0.0242 (10)	0.0237 (10)	0.0083 (9)	−0.0156 (9)	−0.0090 (8)
C1	0.0081 (8)	0.0120 (8)	0.0108 (8)	−0.0009 (6)	−0.0017 (6)	−0.0006 (6)
C2	0.0081 (7)	0.0121 (8)	0.0098 (8)	0.0003 (7)	0.0004 (6)	0.0011 (6)
C3	0.0067 (8)	0.0129 (8)	0.0107 (8)	0.0005 (6)	−0.0001 (6)	0.0011 (6)
C4	0.0075 (7)	0.0137 (9)	0.0172 (10)	−0.0003 (7)	−0.0017 (7)	0.0003 (7)

Geometric parameters (Å, º) top

Pb1—O1ⁱ	2.472 (2)	O3—H3O	0.843 (10)
Pb1—O5ⁱⁱ	2.482 (2)	O4—C3	1.420 (3)
Pb1—O6ⁱⁱⁱ	2.594 (2)	O4—H4O	0.845 (10)
Pb1—O3ⁱ	2.5972 (17)	O5—C4	1.250 (3)
Pb1—O4^iv	2.6878 (19)	O6—C4	1.270 (3)
Pb1—O4ⁱⁱⁱ	2.7866 (19)	C1—C2	1.536 (3)
Pb1—O2^iv	2.935 (2)	C2—C3	1.535 (3)
Pb1—O1	3.004 (2)	C2—H2	0.9800
O1—C1	1.246 (3)	C3—C4	1.522 (3)
O2—C1	1.261 (3)	C3—H3	0.9800
O3—C2	1.411 (3)

O1ⁱ—Pb1—O5ⁱⁱ	72.93 (7)	C1—O1—Pb1^v	126.48 (16)
O1ⁱ—Pb1—O6ⁱⁱⁱ	74.36 (7)	C2—O3—Pb1^v	120.65 (14)
O5ⁱⁱ—Pb1—O6ⁱⁱⁱ	99.96 (9)	C2—O3—H3O	118 (3)
O1ⁱ—Pb1—O3ⁱ	62.88 (6)	Pb1^v—O3—H3O	115 (3)
O5ⁱⁱ—Pb1—O3ⁱ	135.70 (7)	C3—O4—Pb1^vi	108.28 (13)
O6ⁱⁱⁱ—Pb1—O3ⁱ	71.85 (8)	C3—O4—H4O	111 (3)
O1ⁱ—Pb1—O4^iv	64.23 (6)	Pb1^vi—O4—H4O	121 (3)
O5ⁱⁱ—Pb1—O4^iv	69.82 (7)	C4—O5—Pb1^vii	128.07 (19)
O6ⁱⁱⁱ—Pb1—O4^iv	138.58 (7)	C4—O6—Pb1^viii	125.98 (18)
O3ⁱ—Pb1—O4^iv	87.75 (6)	O1—C1—O2	125.1 (2)
O1ⁱ—Pb1—O4ⁱⁱⁱ	122.21 (6)	O1—C1—C2	119.4 (2)
O5ⁱⁱ—Pb1—O4ⁱⁱⁱ	82.70 (7)	O2—C1—C2	115.4 (2)
O6ⁱⁱⁱ—Pb1—O4ⁱⁱⁱ	59.20 (6)	O3—C2—C3	113.16 (19)
O3ⁱ—Pb1—O4ⁱⁱⁱ	123.07 (6)	O3—C2—C1	110.14 (19)
O4^iv—Pb1—O4ⁱⁱⁱ	148.738 (15)	C3—C2—C1	105.30 (18)
O1ⁱ—Pb1—O2^iv	118.51 (7)	O3—C2—H2	109.4
O5ⁱⁱ—Pb1—O2^iv	119.10 (7)	C3—C2—H2	109.4
O6ⁱⁱⁱ—Pb1—O2^iv	140.78 (8)	C1—C2—H2	109.4
O3ⁱ—Pb1—O2^iv	81.74 (7)	O4—C3—C4	111.99 (19)
O4^iv—Pb1—O2^iv	65.93 (6)	O4—C3—C2	110.38 (18)
O4ⁱⁱⁱ—Pb1—O2^iv	119.18 (6)	C4—C3—C2	114.25 (19)
O1ⁱ—Pb1—O1	150.22 (4)	O4—C3—H3	106.6
O5ⁱⁱ—Pb1—O1	77.58 (7)	C4—C3—H3	106.6
O6ⁱⁱⁱ—Pb1—O1	115.47 (6)	C2—C3—H3	106.6
O3ⁱ—Pb1—O1	145.98 (6)	O5—C4—O6	126.2 (3)
O4^iv—Pb1—O1	101.71 (6)	O5—C4—C3	115.9 (2)
O4ⁱⁱⁱ—Pb1—O1	56.54 (5)	O6—C4—C3	117.9 (2)
O2^iv—Pb1—O1	72.91 (6)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3O···O2^vii	0.84 (1)	2.02 (4)	2.646 (3)	131 (5)
O4—H4O···O6^ix	0.85 (1)	1.79 (1)	2.618 (3)	169 (4)

Symmetry codes: (vii) −x+1/2, −y, z+1/2; (ix) x−1/2, −y+1/2, −z+1.

Comparison of the Pb—O bond lengths (Å) in the current and the previous (De Ridder et al., 2002) refinements of lead tartrate. top

For the previous refinement: a = 7.99482 (3), b = 8.84525 (4), c = 8.35318 (4) Å.

Bond	current refinement	previous refinement
Pb—O1ⁱ	2.472 (2)	2.859 (12)
Pb—O5ⁱⁱ	2.482 (2)	2.398 (11)
Pb—O6ⁱⁱⁱ	2.594 (2)	2.575 (12)
Pb—O3ⁱ	2.5972 (17)	2.637 (9)
Pb—O4^iv	2.6878 (19)	2.649 (11)
Pb—O4ⁱⁱⁱ	2.7866 (19)	2.847 (12)
Pb—O2^iv	2.935 (2)	2.975 (13)
Pb—O1	3.004 (2)	2.754 (12)

Symmetry codes: (i) -x - 1/2, -y, z - 1/2; (ii) -x + 1/2, -y, z - 1/2; (iii) -x, y - 1/2, -z + 1/2; (iv) x - 1/2, -y + 1/2, -z.

Acknowledgements

The X-ray centre of the Vienna University of Technology is acknowledged for providing access to the single-crystal and powder X-ray diffractometers.

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