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Volume 66 
Part 2 
Pages m44-m47  
February 2010  

Received 11 December 2009
Accepted 7 January 2010
Online 15 January 2010

Two polymorphs of a lead(II) complex with 8-hydroxy-2-methylquinoline and thiocyanate

aDepartment of Chemistry, General Campus, Shahid Beheshti University, Tehran 1983963113, Iran, and bEnvironmental Inorganic Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-41296 Göteborg, Sweden
Correspondence e-mail: langer@chalmers.se

Two distinct polymorphs of bis([mu]2-methylquinolin-8-olato)-[kappa]3N,O:O;[kappa]3O:N,O-bis[(isothiocyanato-[kappa]N)lead(II)], [Pb2(C10H8NO)2(NCS)2], (I)[link], forming dinuclear complexes from a methanolic solution containing lead(II) nitrate, 2-methylquinolin-8-ol (M-Hq) and KSCN, crystallized concomitantly as colourless prisms [form (Ia)[link]] and long thin colourless needles [form (Ib)[link]]. In both cases, the complexes lie across a centre of inversion. The polymorphs differ substantially in their conformation and in their interactions, viz. Pb...S and [pi]-[pi] for form (Ia)[link] and Pb...S, Pb...[pi] and C-H...[pi] for form (Ib)[link].

Comment

The synthesis of novel organic-inorganic hybrid materials in the field of supramolecular and crystal engineering has been a subject of rapid growth in recent years (Moulton & Zaworotko, 2001[Moulton, B. & Zaworotko, M. J. (2001). Chem. Rev. 101, 1629-1658.]). Bidentate ligands containing soft and hard atoms have potential applications in catalytic and stoichiometric reactions (Kaim & Schwederski, 1995[Kaim, W. & Schwederski, B. (1995). In Bioinorganic Chemistry: Inorganic Elements in the Chemistry of Life. Chichester: Wiley.]), as well as in advanced materials (Soldatov et al., 2004[Soldatov, D. V., Enright, G. D. & Ripmeester, J. A. (2004). Cryst. Growth Des. 4, 1185-1194.]). Recent reports of quinolin-8-ol (Hq) and its derivatives with lead(II) salts include [Pb(q)(NCS)]n (Shahverdizadeh et al., 2008[Shahverdizadeh, G. H., Soudi, A. A., Morsali, A. & Retailleau, P. (2008). Inorg. Chim. Acta, 361, 1875-1884.]), [Pb2(M-q)2(NO3)2(CH3OH)2] (M-q is 2-methylquinolin-8-olate; Mohammadnezhad et al., 2009a[Mohammadnezhad, Sh. G., Amini, M. M. & Ng, S. W. (2009a). Acta Cryst. E65, m259.]), [Pb2(M-q)2(C2H3O2)2] (Mohammadnezhad et al., 2009b[Mohammadnezhad, Sh. G., Amini, M. M. & Ng, S. W. (2009b). Acta Cryst. E65, m260.]), [Pb2(Cl-q)2(C2H3O2)2] (Cl-q is 5-chloroquinolin-8-olate; Mohammadnezhad et al., 2009c[Mohammadnezhad, Sh. G., Amini, M. M. & Ng, S. W. (2009c). Acta Cryst. E65, m261.]) and [Pb4(q)6(NO3)2] (Zhang et al., 2008[Zhang, W.-Z., Wei, D.-Z., Che, X.-F., Gao, E.-J., Wang, K.-H., Yin, H.-X. & Gu, X.-G. (2008). Chin. J. Struct. Chem. 27, 287-292.]).

As part of our interest in exploring the effect of steric hindrance in lead(II) complexes with mixed ligands, we have examined isothiocyanate due to its various coordination modes, i.e. single or bridging coordination through S, N or both, in the presence of 2-methylquinolin-8-ol (M-Hq). In this paper, we report the crystal structures of two polymorphs of [Pb(M-q)(NCS)]2, (Ia)[link] and (Ib)[link], which show that the steric hindrance of a methyl group leads to the coordination of isothiocyanate only via the N atom, not via the S atom, in contrast with the bidentate coordination observed in [Pb(q)(NCS)]n (Shahverdizadeh et al., 2008[Shahverdizadeh, G. H., Soudi, A. A., Morsali, A. & Retailleau, P. (2008). Inorg. Chim. Acta, 361, 1875-1884.]).

[Scheme 1]

Polymorph (Ia)[link] crystallizes in the triclinic space group P[\overline{1}], while polymorph (Ib)[link] crystallizes concomitantly in the monoclinic space group P21/c. Perspective drawings of these compounds are shown in Figs. 1[link] and 2[link], respectively; in both cases, the Pb2O2 core lies across the crystallographic inversion centre. In both structures, the PbII ion is four-coordinated, with the M-q ligand acting as a bidentate chelate, along with a bridging phenoxy O atom and the N atom from the isothiocyanate. As expected, these four coordinating atoms around the PbII centre in both polymorphs show a hemidirected geometry with a stereochemically active lone pair. Selected bond distances and bond angles are presented in Table 1[link]. It is notable that the major structural difference between these two polymorphs is the NCS coordination angle. In (Ia)[link], the Pb1-N2-C1 angle is 149.7 (4)°, in contrast with a value of 136.8 (6)° in (Ib)[link]. All other angles except O1-Pb1-N2, N2-Pb1-O1i and O1i-Pb1-N1 are similar [symmetry code: (i) -x, -y + 1, -z + 1 for (Ia)[link]; (i) -x + 1, -y + 2, -z + 1 for (Ib)[link]]. The different conformations of the polymorphs are strongly reflected in the torsion angles containing thiocyanate atoms N2 and C1, but also in the torsion angle Pb1-O1-C8-C7 (see Table 1[link]). The Pb...Pb distances are 3.9397 (3) and 4.0212 (14) Å for (Ia)[link] and (Ib)[link], respectively.

Interestingly, in contrast with the previously reported coordination polymer [Pb(q)(SCN)]n (Shahverdizadeh et al., 2008[Shahverdizadeh, G. H., Soudi, A. A., Morsali, A. & Retailleau, P. (2008). Inorg. Chim. Acta, 361, 1875-1884.]), the steric hindrance imposed by the methyl group at the C2 position prevents the coordination of SCN as a bidentate ligand. Indeed, the larger S atom is unable to coordinate to the PbII ion in either case, and hence the polymeric nature is disrupted and the coordination number decreases to four. Nevertheless, Pb...S interactions are formed for Pb1...S1ii and Pbiv...S1iii [3.6009 (14) Å] and for Pb1...S1iii and Pbiv...S1ii [3.6649 (14) Å] in compound (Ia)[link] (Fig. 3[link]) [symmetry codes: (ii) 1 + x, y, z; (iii) -1 - x, 1 - y, 2 - z; (iv) -x, 1 - y, 2 - z]. Different types of interaction are seen in polymorph (Ib)[link]. In addition to Pb...S interactions with distances of 3.506 (3) Å, an interaction is observed between the PbII ion and the centroid (Cg) of the C5-C10 benzene ring in the molecule at the symmetry position (x, y + 1, z), with Pb...Cg = 3.171 Å (Fig. 4[link]).

Structure (Ia)[link] contains sheets of molecules in the ac plane held together by Pb...S interactions (Fig. 5[link]). The sheets have the aromatic wings of the ligand protruding from each side and interdigitate to provide [pi]-[pi] stacking, with perpendicular distances of 3.288 and 3.377 Å (Fig. 6[link]), reflecting the different positions of the N atoms in the overlapping heterocyclic rings.

In contrast, structure (Ib)[link] contains chains of molecules along b which are held together by Pb...S and Pb...ring interactions. The aromatic surfaces protruding from these chains make a herringbone formation in the bc plane (Fig. 7[link]), with C-H...[pi] interactions for enhancement [between C6-H6 and the centroid (Cg) of the C5-C10 ring at symmetry position (-x + 1, y - [{1\over 2}], -z + [{3\over 2}]), with C6...Cg = 3.458 (7) Å, H6...Cg = 2.70 Å and C6-H6...Cg = 137°].

[Figure 1]
Figure 1
The structure of polymorph (Ia)[link], showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry code: (i) -x, -y + 1, -z + 1.]
[Figure 2]
Figure 2
The structure of polymorph (Ib)[link], showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry code: (i) -x + 1, -y + 2, -z + 1.]
[Figure 3]
Figure 3
The Pb...S interactions (dashed lines) in (Ia)[link]. [Symmetry codes: (ii) 1 + x, y, z; (iii) -1 - x, 1 - y, 2 - z; (iv) -x, 1 - y, 2 - z.]
[Figure 4]
Figure 4
The Pb...S interactions (dashed lines) in (Ib)[link], with distances of 3.506 (3) Å. The distance from atom Pb1 to the centroid of the C5-C10 ring of an adjacent molecule (also dashed lines) is 3.171 Å. [Symmetry codes: (i) -x + 1, -y + 2, -z + 1; (ii) x, y + 1, z.]
[Figure 5]
Figure 5
The contents of the unit cell of (Ia)[link], in a projection parallel to the quinoline rings.
[Figure 6]
Figure 6
The [pi]-[pi] interactions in (Ia)[link]. The overlap of the quinoline rings with a perpendicular distance of 3.288 Å is shown in the upper part, and that with a perpendicular distance of 3.377 Å is shown in the lower part.
[Figure 7]
Figure 7
The herringbone formation of the aromatic surfaces in (Ib)[link]. H atoms have been omitted for clarity.

Experimental

Lead nitrate (0.33 g, 1 mmol), 2-methylquinolin-8-ol (0.16 g, 1 mmol) and KSCN (0.19 g, 2 mmol) were loaded into a convection tube. The tube was filled carefully with methanol and kept at 333 K. Crystals were collected from the side arm after several days; they were a mixture of large crystals of KNO3, colourless prisms of (Ia)[link] and long thin colourless needles of (Ib)[link].

Polymorph (Ia)[link]

Crystal data
  • [Pb2(C10H8NO)2(NCS)2]

  • Mr = 846.89

  • Triclinic, [P \overline 1]

  • a = 7.8556 (5) Å

  • b = 8.4155 (5) Å

  • c = 9.1550 (6) Å

  • [alpha] = 78.524 (1)°

  • [beta] = 69.771 (1)°

  • [gamma] = 82.813 (1)°

  • V = 555.50 (6) Å3

  • Z = 1

  • Mo K[alpha] radiation

  • [mu] = 15.35 mm-1

  • T = 173 K

  • 0.43 × 0.21 × 0.06 mm

Data collection
  • Siemens SMART CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. Version 2.10. University of Göttingen, Germany.]) Tmin = 0.095, Tmax = 0.399

  • 9987 measured reflections

  • 3889 independent reflections

  • 3475 reflections with I > 2[sigma](I)

  • Rint = 0.046

Refinement
  • R[F2 > 2[sigma](F2)] = 0.030

  • wR(F2) = 0.072

  • S = 1.00

  • 3889 reflections

  • 146 parameters

  • H-atom parameters constrained

  • [Delta][rho]max = 2.27 e Å-3

  • [Delta][rho]min = -3.09 e Å-3

Polymorph (Ib)[link]

Crystal data
  • [Pb2(C10H8NO)2(NCS)2]

  • Mr = 846.89

  • Monoclinic, P 21 /c

  • a = 12.037 (5) Å

  • b = 5.731 (2) Å

  • c = 16.327 (6) Å

  • [beta] = 90.368 (7)°

  • V = 1126.3 (7) Å3

  • Z = 2

  • Mo K[alpha] radiation

  • [mu] = 15.14 mm-1

  • T = 173 K

  • 0.96 × 0.04 × 0.02 mm

Data collection
  • Siemens SMART CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. Version 2.10. University of Göttingen, Germany.]) Tmin = 0.102, Tmax = 0.752

  • 12903 measured reflections

  • 3502 independent reflections

  • 2528 reflections with I > 2[sigma](I)

  • Rint = 0.078

Refinement
  • R[F2 > 2[sigma](F2)] = 0.038

  • wR(F2) = 0.090

  • S = 1.01

  • 3502 reflections

  • 146 parameters

  • H-atom parameters constrained

  • [Delta][rho]max = 2.42 e Å-3

  • [Delta][rho]min = -3.27 e Å-3

Table 1
Selected geometric parameters (Å, °) for (Ia)[link] and (Ib)[link]

  (Ia)[link] (Ib)[link]
Pb1-O1 2.272 (3) 2.295 (4)
Pb1-Oi 2.459 (3) 2.504 (4)
Pb1-N1 2.499 (4) 2.540 (5)
Pb1-N2 2.418 (4) 2.393 (6)
     
Pb1-O1-Pb1i 112.70 (11) 113.76 (18)
O1-Pb1-O1i 67.30 (11) 66.24 (18)
O1-Pb1-N1 69.09 (11) 68.97 (16)
O1-Pb1-N2 101.34 (15) 88.8 (2)
N1-Pb1-N2 80.77 (14) 80.6 (2)
N1-Pb1-O1i 128.43 (11) 134.17 (16)
N2-Pb1-O1i 82.10 (13) 89.17 (19)
Pb1-N2-C1 149.7 (4) 136.8 (6)
     
N1-Pb1-O1-C8 10.5 (3) 1.6 (4)
N1-Pb1-O1-Pb1i -151.77 -170.1 (2)
N2-Pb1-O1-C8 85.9 (3) 82.0 (5)
N2-Pb1-O1-Pb1i -76.35 (16) -89.7 (2)
O1i-Pb1-O1-C8 162.2 (4) 171.7 (5)
O1-Pb1-N1-C2 178.1 (4) -178.8 (6)
O1-Pb1-N1-C9 -9.2 (3) -2.9 (4)
N2-Pb1-N1-C2 72.1 (4) 88.9 (5)
N2-Pb1-N1-C9 -115.2 (3) -95.2 (4)
O1i-Pb1-N1-C2 144.3 (4) 168.5 (5)
O1i-Pb1-N1-C9 -43.1 (4) -15.6 (5)
O1-Pb1-N2-C1 -159.3 (7) -68.8 (8)
N1-Pb1-N2-C1 -92.9 (7) 0.1 (8)
O1i-Pb1-N2-C1 135.9 (8) -135.0 (8)
O1-Pb1-O1i-C8i 161.3 (4) 171.3 (5)
N1-Pb1-O1i-Pb1i 34.3 (2) 13.0 (3)
N1-Pb1-O1i-C8i -164.4 (3) -175.7 (4)
N2-Pb1-O1i-Pb1i 105.85 (17) 89.0 (2)
N2-Pb1-O1i-C8i -92.8 (4) -99.7 (5)
Pb1-O1-C8-C7 169.5 (4) -178.9 (5)
Pb1-O1-C8-C9 -10.9 (6) -0.2 (8)
Pb1i-O1-C8-C7 -30.5 (6) -8.2 (8)
Pb1i-O1-C8-C9 149.2 (3) 170.5 (4)
Pb1-N1-C2-C3 172.4 (3) 174.1 (5)
Pb1-N1-C2-C11 -8.6 (6) -8.8 (9)
Pb1-N1-C9-C8 7.6 (5) 3.9 (7)
Pb1-N1-C9-C10 -171.8 (3) -176.8 (5)
Symmetry codes: (i) -x, -y + 1, -z + 1 for (Ia)[link]; (i) -x + 1, -y + 2, -z + 1 for (Ib)[link].

Aromatic H atoms were included in the model with Uiso(H) = 1.2Ueq(C), and their positions were constrained to ideal geometry using an appropriate riding model, with C-H = 0.95 Å. For methyl groups, N-C-H angles (109.5°) were kept fixed, while the torsion angle was allowed to refine, with the starting positions based on the circular Fourier synthesis averaged using the local threefold axis; C-H = 0.98 Å and Uiso(H) = 1.5Ueq(C).

For both polymorphs, data collection: SMART (Bruker, 2003[Bruker (2003). SMART (Version 5.63) and SAINT (Version 6.45). Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2003[Bruker (2003). SMART (Version 5.63) and SAINT (Version 6.45). Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT and SADABS (Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. Version 2.10. University of Göttingen, Germany.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: DIAMOND (Brandenburg, 2009[Brandenburg, K. (2009). DIAMOND. Version 3.2c. Crystal Impact GbR, Bonn, Germany.]); software used to prepare material for publication: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]).


Supplementary data for this paper are available from the IUCr electronic archives (Reference: SF3124 ). Services for accessing these data are described at the back of the journal.


Acknowledgements

The authors thank Shahid Beheshti University for supporting this study.

References

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Bruker (2003). SMART (Version 5.63) and SAINT (Version 6.45). Bruker AXS Inc., Madison, Wisconsin, USA.
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Sheldrick, G. M. (2003). SADABS. Version 2.10. University of Göttingen, Germany.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.  [CrossRef] [details]
Soldatov, D. V., Enright, G. D. & Ripmeester, J. A. (2004). Cryst. Growth Des. 4, 1185-1194.  [CSD] [CrossRef] [ChemPort]
Zhang, W.-Z., Wei, D.-Z., Che, X.-F., Gao, E.-J., Wang, K.-H., Yin, H.-X. & Gu, X.-G. (2008). Chin. J. Struct. Chem. 27, 287-292.  [CrossRef] [ChemPort]


Acta Cryst (2010). C66, m44-m47   [ doi:10.1107/S010827011000096X ]