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In the title compound, [Pb(C12H8NO2)2]n, the Pb atom sits on a crystallographic C2 axis and is six-coordinate, ligated by two chelating carboxyl­ate groups from two 3-(pyridin-4-yl)benzoate (L) ligands and by two N atoms from another two ligands. Each ligand bridges two PbII centres, extending the structure into a corrugated two-dimensional (4,4) net. The ligand L is conformationally chiral, with a torsion angle of 27.9 (12)° between the planes of its two rings. The torsion angle has the same sense throughout the structure, so that the extended two-dimensional polymer is homochiral. Investigation of the thermal stability shows that the network is stable up to 613 K. In the absence of any stereoselective factor in the preparation of the compound, the enanti­omeric purity of the crystal studied, based only on the torsional conformation of the ligand, implies that the bulk sample is a racemic conglomerate.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270113019045/fa3319sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270113019045/fa3319Isup2.hkl
Contains datablock I

CCDC reference: 962904

Introduction top

Chiral multifunctional materials are presently the object of research efforts in several areas (Xuan et al., 2012). An effective and simple strategy for introducing chirality into coordination compounds is the self-assembly of metal ions and ligands into asymmetrical frameworks (Che et al., 2009; Han & Hong, 2005). To this end, it is useful to employ bridging ligands with labile conformations, including chiral conformers, which together with metal centers may form homochiral crystals through spontaneous chiral resolution (Liu et al., 2007). 3-(Pyridin-4-yl)benzoic acid (L), which combines a pyridyl fragment with a benzoic acid group, is a typical unsymmetrical spacer, and has variable conformations resulting from free rotation about the bond joining the pyridyl and phenyl groups. If the two rings are neither coplanar nor mutually perpendicular in a given compound, L will have conformational chirality. So this ligand is a good candidate for use in attempts to obtain chiral metal–organic structures. So far, ligand L has been experimentally observed to form several helical coordination polymers where the left- and right-handed metal–organic helical chains are inter­woven to form meso compounds (Wu et al., 2011; Luo et al., 2007). We report here the synthesis, structure and thermal stability of a lead(II) complex of L, viz. [Pb(L)2]n, (I). Inter­estingly, on crystallization there appears to have been spontaneous resolution into a racemic conglomerate of enanti­opure crystals. Moreover, this homochiral crystal of (I) does not display a helical structure but is formed by a corrugated, chiral two-dimensional metal–organic network.

Experimental top

Synthesis and crystallization top

For the preparation of (I), a mixture of Pb(NO3)2 (0.033 g, 0.1 mmol), L (0.040 g, 0.2 mmol), NaOH (0.008 g, 0.2 mmol) and deionized water (10 ml) was sealed in a 25 ml Teflon-lined stainless steel autoclave. The autoclave was heated at 433 K for 3 d and then cooled slowly to room temperature. Colourless needle-like crystals of (I) suitable for X-ray analysis were obtained in 76% yield (based on Pb). IR spectra in the range of 400–4000 cm-1 were recorded from KBr pellets using a Bruker VECTOR22 spectrophotometer. Selected IR bands (cm-1): 3441 (w), 1691 (m), 1605 (s), 1554 (m), 1429 (w), 1383 (s), 1268 (m), 1067 (w), 765 (s), 676 (w).

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were positioned geometrically and allowed to ride on their parent atoms. In all cases, Uiso(H) values were taken as 1.2 Ueq(C).

Results and discussion top

In (I), the six-coordinate PbII atom sits on a crystallographic twofold axis and has an irregular coordination sphere, which can be described as having a four-legged sawhorse geometry. The legs of the sawhorse are formed by bonds from Pb1 to the O atoms of two chelating carboxyl­ate groups of two L ligands, while the crossbeam, distorted from linearity [N1—Pb—N1iii = 154.9 (4)°; see Table 2 for all symmetry codes], comprises bonds from Pb1 to the pyridine N atoms of another two symmetry-related L ligands (Fig. 1). The bond lengths about atom Pb1 range from 2.345 (8) to 2.733 (8) Å (Table 2), in agreement with those reported for PbII coordination polymers with aromatic carb­oxy­lic acids (Severance et al., 2012). The O1ii—Pb1—O2ii angle of 51.0 (3)° in the four-membered chelate is typical of such fragments, while the N—Pb1—O and the remaining O—Pb1—O angles fall in the wide range of 73.0 (2)–126.4 (2)°, reflecting the irregularity of the sawhorse geometry.

In (I), the deprotonated ligands L, which bridge pairs of PbII atoms, do not possess the achiral conformations with Cs symmetry that might be expected of the free ligand, but rather are twisted about the C6—C8 bond into chiral conformers with C1 symmetry [C5—C6—C8—C9 = 27.9 (12)°]. As the space group (C2) possesses only proper symmetry elements, the sense of this torsion angle is the same throughout the crystal, which is thus enanti­omerically pure.

In all, each PbII center is coordinated by four different symmetry-related L fragments, while each ligand bridges two symmetry-related PbII centers. The overall structure is a homochiral two-dimensional metal–organic polymer with corrugated (4,4) nets (Fig. 2). This is different from the previously reported helical metal–organic structures incorporating ligands L. The separation of the adjacent metal ions bridged by a given ligand L is 11.6710 (5) Å. The two-dimensional net is distorted, as can be characterized by the diagonal Pb···Pb distances within a given four-membered (Pb) ring. With reference to Fig. 2, the diagonal distance Pb1···Pb1v of 13.5534 (6) Å is markedly shorter than the other diagonal distance Pb1i···Pb1ii, which is 19.0040 (8) Å. Inter­estingly, two equivalent nets are mutually inter­penetrated, thus giving a twofold inter­penetrating homochiral fabric (Fig. 3). These layers are stacked along the a axis (Fig. 4). The formation of chiral crystals (I) upon crystallization from what was presumably a racemate implies spontaneous chiral resolution. The refined absolute structure parameter (Flack, 1983) of 0.015 (18) indicates that the resolution was essentially complete. Although individual crystals are stereochemically pure, the bulk compound is expected to be a racemic conglomerate.

To examine the thermal stability of the solid, thermogravimetric analysis (TGA) of a crystalline sample was carried out under an air atmosphere from 303 to 900 K with a heating rate of 10 K min-1. As shown in Fig. 5, compound (I) is stable up to 613 K. Complete decomposition of (I) occurs in the temperature range 613–793 K. The remaining 37.62% may be PbO, in good agreement with the theoretical value of 36.98%. These TGA results indicate that the two-dimensional polymeric framework of (I) is stable up to 613 K.

Related literature top

For chiral metal-organic materials, see: Xuan, et al. (2012). For construction of homochiral conglomerates based on metal-organic helices, see: Che, et al. (2009); Han, et al. (2005); Liu, et al. (2007). For helical coordination polymers of 3-pyridin-4-ylbenzoicate ligand, see: Wu, et al. (2011); Luo, et al. (2007). For the bond distances, see: Severance, et al. (2012). For confirmation of spontaneous resolution, see: Flack, (1983).

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1994); data reduction: SAINT (Siemens, 1994); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Siemens, 1994); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The coordination environment of the PbII atom in (I). Displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes: (i) x, y+1, z+1; (ii) -x, y+1, -z; (iii) -x, y, -z+1.]
[Figure 2] Fig. 2. The homochiral corrugated (4,4) net in (I). [Symmetry codes: (i) x, y+1, z+1; (ii) -x, y+1, -z; (v) x, y+2, z.]
[Figure 3] Fig. 3. (a) The twofold interpenetrating homochiral network structure in (I). (b) A simplified scheme indicating the twofold interpenetration of the two-dimensional metal–organic polymer. The orientation of these drawings is the same as that of Fig. 2.
[Figure 4] Fig. 4. The stacking of the chiral layers in (I).
[Figure 5] Fig. 5. The TGA curve for (I).
Poly[bis[µ2-3-(pyridin-4-yl)benzoato-κ3N:O,O']lead(II)] top
Crystal data top
[Pb(C12H8NO2)2]F(000) = 576
Mr = 603.58Dx = 2.013 Mg m3
Monoclinic, C2Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C 2yCell parameters from 2390 reflections
a = 15.9945 (7) Åθ = 3.0–26.0°
b = 6.7767 (3) ŵ = 8.51 mm1
c = 9.5020 (4) ÅT = 296 K
β = 104.795 (2)°Block, colourless
V = 995.77 (7) Å30.41 × 0.10 × 0.07 mm
Z = 2
Data collection top
Siemens SMART CCD
diffractometer
1676 independent reflections
Radiation source: fine-focus sealed tube1668 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.041
ω scanθmax = 25.0°, θmin = 2.2°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 1818
Tmin = 0.350, Tmax = 0.612k = 78
3618 measured reflectionsl = 1011
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)] = 0.032H-atom parameters constrained
wR(F2) = 0.075 w = 1/[σ2(Fo2) + (0.0097P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.10(Δ/σ)max < 0.001
1676 reflectionsΔρmax = 0.98 e Å3
141 parametersΔρmin = 1.93 e Å3
1 restraintAbsolute structure: Flack (1983), ???? Friedel pairs
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.015 (18)
Crystal data top
[Pb(C12H8NO2)2]V = 995.77 (7) Å3
Mr = 603.58Z = 2
Monoclinic, C2Mo Kα radiation
a = 15.9945 (7) ŵ = 8.51 mm1
b = 6.7767 (3) ÅT = 296 K
c = 9.5020 (4) Å0.41 × 0.10 × 0.07 mm
β = 104.795 (2)°
Data collection top
Siemens SMART CCD
diffractometer
1676 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
1668 reflections with I > 2σ(I)
Tmin = 0.350, Tmax = 0.612Rint = 0.041
3618 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.032H-atom parameters constrained
wR(F2) = 0.075Δρmax = 0.98 e Å3
S = 1.10Δρmin = 1.93 e Å3
1676 reflectionsAbsolute structure: Flack (1983), ???? Friedel pairs
141 parametersAbsolute structure parameter: 0.015 (18)
1 restraint
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
Pb10.00000.23740.50000.03977 (15)
O10.0598 (5)0.5374 (12)0.3142 (10)0.071 (2)
O20.1223 (7)0.4909 (13)0.4902 (9)0.085 (3)
N10.0774 (5)0.1497 (12)0.2823 (9)0.0463 (19)
C10.1082 (6)0.4371 (15)0.3746 (12)0.049 (2)
C20.1433 (5)0.250 (4)0.3032 (8)0.041 (2)
C30.1938 (6)0.1221 (15)0.3646 (10)0.047 (2)
H30.20910.15930.44880.056*
C40.2204 (6)0.0561 (15)0.3016 (10)0.046 (2)
H40.25340.13920.34390.055*
C50.1986 (6)0.1155 (14)0.1742 (10)0.042 (2)
H50.21660.23770.13280.050*
C60.1495 (5)0.0107 (13)0.1094 (9)0.0349 (17)
C70.1232 (5)0.1901 (13)0.1747 (10)0.039 (2)
H70.09100.27430.13180.047*
C80.1249 (5)0.0463 (13)0.0260 (9)0.0355 (18)
C90.1149 (5)0.239 (4)0.0627 (8)0.0447 (16)
H90.12410.34010.00230.054*
C100.0909 (7)0.2842 (14)0.1897 (13)0.053 (4)
H100.08400.41630.21070.063*
C110.0876 (6)0.0373 (15)0.2471 (10)0.045 (2)
H110.07870.13510.31040.054*
C120.1108 (6)0.0959 (14)0.1225 (9)0.0406 (19)
H120.11680.22910.10370.049*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Pb10.0582 (2)0.0347 (2)0.0326 (2)0.0000.02288 (15)0.000
O10.086 (5)0.048 (5)0.086 (6)0.021 (4)0.035 (5)0.023 (4)
O20.147 (8)0.066 (6)0.053 (5)0.028 (5)0.045 (5)0.035 (4)
N10.058 (5)0.049 (5)0.037 (5)0.000 (3)0.022 (4)0.008 (3)
C10.054 (5)0.038 (5)0.055 (6)0.004 (4)0.012 (5)0.011 (4)
C20.045 (3)0.050 (6)0.031 (3)0.002 (8)0.018 (3)0.016 (7)
C30.051 (5)0.060 (7)0.038 (5)0.006 (4)0.027 (4)0.005 (4)
C40.052 (5)0.054 (6)0.041 (5)0.011 (4)0.029 (4)0.002 (4)
C50.043 (4)0.049 (6)0.036 (5)0.007 (4)0.013 (4)0.005 (4)
C60.034 (4)0.044 (5)0.030 (4)0.000 (3)0.016 (3)0.003 (3)
C70.043 (4)0.045 (6)0.035 (5)0.002 (3)0.022 (4)0.003 (3)
C80.033 (4)0.043 (5)0.032 (4)0.003 (3)0.011 (3)0.004 (3)
C90.061 (4)0.041 (4)0.041 (4)0.004 (11)0.030 (3)0.006 (10)
C100.069 (6)0.041 (11)0.055 (6)0.003 (4)0.029 (5)0.007 (4)
C110.048 (5)0.056 (6)0.035 (5)0.002 (4)0.018 (4)0.004 (4)
C120.050 (5)0.046 (5)0.031 (4)0.002 (4)0.020 (4)0.005 (3)
Geometric parameters (Å, º) top
Pb1—O1i2.345 (8)C3—C41.367 (15)
Pb1—O1ii2.345 (7)C3—H30.9300
Pb1—O2ii2.670 (9)C4—C51.401 (13)
Pb1—O2i2.670 (9)C4—H40.9300
Pb1—N12.733 (8)C5—C61.406 (13)
Pb1—N1iii2.733 (8)C5—H50.9300
Pb1—C1i2.868 (9)C6—C71.381 (13)
Pb1—C1ii2.868 (9)C6—C81.489 (11)
O1—C11.271 (14)C7—H70.9300
O1—Pb1iv2.345 (7)C8—C91.37 (3)
O2—C11.232 (13)C8—C121.387 (13)
O2—Pb1iv2.670 (9)C9—C101.390 (14)
N1—C101.322 (13)C9—H90.9300
N1—C111.332 (13)C10—H100.9300
C1—C21.48 (2)C11—C121.386 (13)
C1—Pb1iv2.868 (9)C11—H110.9300
C2—C71.399 (12)C12—H120.9300
C2—C31.41 (2)
O1i—Pb1—O1ii98.8 (5)O2—C1—Pb1iv68.3 (6)
O1i—Pb1—O2ii74.4 (3)O1—C1—Pb1iv53.4 (5)
O1ii—Pb1—O2ii51.0 (3)C2—C1—Pb1iv165.4 (7)
O1i—Pb1—O2i51.0 (3)C7—C2—C3118.0 (16)
O1ii—Pb1—O2i74.4 (3)C7—C2—C1120.1 (13)
O2ii—Pb1—O2i92.8 (5)C3—C2—C1121.8 (8)
O1i—Pb1—N1122.3 (3)C4—C3—C2120.5 (10)
O1ii—Pb1—N175.4 (3)C4—C3—H3119.7
O2ii—Pb1—N1126.4 (2)C2—C3—H3119.7
O2i—Pb1—N173.0 (2)C3—C4—C5121.0 (8)
O1i—Pb1—N1iii75.4 (3)C3—C4—H4119.5
O1ii—Pb1—N1iii122.3 (3)C5—C4—H4119.5
O2ii—Pb1—N1iii73.0 (2)C4—C5—C6119.6 (8)
O2i—Pb1—N1iii126.4 (2)C4—C5—H5120.2
N1—Pb1—N1iii154.9 (4)C6—C5—H5120.2
O1i—Pb1—C1i25.8 (3)C7—C6—C5118.6 (8)
O1ii—Pb1—C1i84.2 (3)C7—C6—C8120.0 (7)
O2ii—Pb1—C1i81.0 (3)C5—C6—C8121.4 (8)
O2i—Pb1—C1i25.4 (3)C6—C7—C2122.3 (11)
N1—Pb1—C1i98.0 (3)C6—C7—H7118.8
N1iii—Pb1—C1i101.2 (3)C2—C7—H7118.8
O1i—Pb1—C1ii84.2 (3)C9—C8—C12116.3 (8)
O1ii—Pb1—C1ii25.8 (3)C9—C8—C6122.7 (9)
O2ii—Pb1—C1ii25.4 (3)C12—C8—C6121.0 (8)
O2i—Pb1—C1ii81.0 (3)C8—C9—C10120.4 (17)
N1—Pb1—C1ii101.2 (3)C8—C9—H9119.8
N1iii—Pb1—C1ii98.0 (3)C10—C9—H9119.8
C1i—Pb1—C1ii79.5 (4)N1—C10—C9123.7 (14)
C1—O1—Pb1iv100.8 (7)N1—C10—H10118.2
C1—O2—Pb1iv86.3 (7)C9—C10—H10118.2
C10—N1—C11115.9 (8)N1—C11—C12124.3 (9)
C10—N1—Pb1122.4 (6)N1—C11—H11117.8
C11—N1—Pb1120.4 (6)C12—C11—H11117.8
O2—C1—O1121.0 (9)C11—C12—C8119.3 (9)
O2—C1—C2121.9 (10)C11—C12—H12120.3
O1—C1—C2117.1 (9)C8—C12—H12120.3
O1i—Pb1—N1—C1061.6 (9)C7—C2—C3—C41.4 (17)
O1ii—Pb1—N1—C1029.6 (8)C1—C2—C3—C4175.5 (11)
O2ii—Pb1—N1—C1032.4 (9)C2—C3—C4—C50.4 (16)
O2i—Pb1—N1—C1048.2 (8)C3—C4—C5—C60.7 (15)
N1iii—Pb1—N1—C10168.0 (8)C4—C5—C6—C70.7 (13)
C1i—Pb1—N1—C1052.2 (8)C4—C5—C6—C8180.0 (8)
C1ii—Pb1—N1—C1028.6 (8)C5—C6—C7—C20.4 (14)
O1i—Pb1—N1—C11131.8 (7)C8—C6—C7—C2179.0 (9)
O1ii—Pb1—N1—C11137.0 (7)C3—C2—C7—C61.4 (16)
O2ii—Pb1—N1—C11134.1 (7)C1—C2—C7—C6175.6 (10)
O2i—Pb1—N1—C11145.2 (8)C7—C6—C8—C9151.5 (8)
N1iii—Pb1—N1—C111.4 (7)C5—C6—C8—C927.9 (12)
C1i—Pb1—N1—C11141.2 (7)C7—C6—C8—C1228.4 (12)
C1ii—Pb1—N1—C11138.0 (7)C5—C6—C8—C12152.2 (8)
Pb1iv—O2—C1—O19.0 (11)C12—C8—C9—C100.6 (12)
Pb1iv—O2—C1—C2168.2 (10)C6—C8—C9—C10179.3 (8)
Pb1iv—O1—C1—O210.5 (12)C11—N1—C10—C90.4 (15)
Pb1iv—O1—C1—C2166.9 (9)Pb1—N1—C10—C9167.5 (7)
O2—C1—C2—C7177.6 (12)C8—C9—C10—N10.8 (15)
O1—C1—C2—C70.3 (17)C10—N1—C11—C120.1 (14)
Pb1iv—C1—C2—C746 (4)Pb1—N1—C11—C12167.3 (7)
O2—C1—C2—C30.8 (19)N1—C11—C12—C80.2 (14)
O1—C1—C2—C3176.6 (11)C9—C8—C12—C110.2 (12)
Pb1iv—C1—C2—C3130 (3)C6—C8—C12—C11179.7 (8)
Symmetry codes: (i) x, y+1, z+1; (ii) x, y+1, z; (iii) x, y, z+1; (iv) x, y1, z1.

Experimental details

Crystal data
Chemical formula[Pb(C12H8NO2)2]
Mr603.58
Crystal system, space groupMonoclinic, C2
Temperature (K)296
a, b, c (Å)15.9945 (7), 6.7767 (3), 9.5020 (4)
β (°) 104.795 (2)
V3)995.77 (7)
Z2
Radiation typeMo Kα
µ (mm1)8.51
Crystal size (mm)0.41 × 0.10 × 0.07
Data collection
DiffractometerSiemens SMART CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.350, 0.612
No. of measured, independent and
observed [I > 2σ(I)] reflections
3618, 1676, 1668
Rint0.041
(sin θ/λ)max1)0.594
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.032, 0.075, 1.10
No. of reflections1676
No. of parameters141
No. of restraints1
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.98, 1.93
Absolute structureFlack (1983), ???? Friedel pairs
Absolute structure parameter0.015 (18)

Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1994), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Siemens, 1994).

Selected geometric parameters (Å, º) top
Pb1—O1i2.345 (8)Pb1—N12.733 (8)
Pb1—O2i2.670 (9)
O1i—Pb1—O1ii98.8 (5)O1ii—Pb1—N175.4 (3)
O1i—Pb1—O2ii74.4 (3)O2ii—Pb1—N1126.4 (2)
O1ii—Pb1—O2ii51.0 (3)O2i—Pb1—N173.0 (2)
O2ii—Pb1—O2i92.8 (5)N1—Pb1—N1iii154.9 (4)
O1i—Pb1—N1122.3 (3)
Symmetry codes: (i) x, y+1, z+1; (ii) x, y+1, z; (iii) x, y, z+1.
 

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