In(SAr)3 As a Building Block for 3D and Helical Coordination Polymers

Article pubs.acs.org/crystal

In(SAr)3 As a Building Block for 3D and Helical Coordination Polymers Johanna Heine,† Małgorzata Hołyńska,† Marco Reuter,‡ Benedikt Haas,‡ Sangam Chatterjee,‡ Martin Koch,‡ Katharina I. Gries,‡ Kerstin Volz,‡ and Stefanie Dehnen*,† †

Fachbereich Chemie and Wissenschaftliches Zentrum für Materialwissenschaften (WZMW), Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany ‡ Fachbereich Physik and Wissenschaftliches Zentrum für Materialwissenschaften (WZMW), Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany S Supporting Information *

ABSTRACT: In(SAr)3 (Ar = phenyl or p-tolyl) was employed as a building block to construct coordination polymers [(In(SPh)3)3(tpt)2] (1, tpt = 2,4,6-tris(4-pyridyl)triazine), [In(SPh)2(2-PCIH)] (2, 2-HPCIH = 2-pyridinecarbaldehyde isonicotinoylhydrazone), and [(In(S(p-tol))2)(2PCIH)]·2MeOH (3). Compound 1 is an intricate 3D coordination polymer displaying superstructure effects on its X-ray diffraction pattern, which have been additionally studied by transmission electron microscopy (TEM). Compounds 2 and 3 are helical coordination polymers. Whereas 3 comprises helices of both rotational handednesses in its crystal structure, 2 possesses only one enantiomeric form and thus exhibits a noncentrosymmetric structure that displays an SHG effect.

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INTRODUCTION Metal−organic frameworks (MOFs) and coordination polymers (CPs) have become a large and fast growing field of research in the past decade.1 The hybrid nature of these materials, combining the characteristics of their organic and inorganic building blocks, provides features such as porosity,2 luminescence,3 or useful magnetic4 or optical properties,5 enabling their use in gas storage6 and separation,7 heterogeneous catalysis,8 sensors,9 or biomedical applications.10 While a great number of MOFs and CPs incorporating transition metals are known, main group metals have received far less attention, although a number of interesting examples exist.11 Metal thiolates represent a versatile and widely investigated class of compounds with relevance to fundamental biochemical processes,12 potential applications as precursors for sulfide materials,13 and the capability to form a multitude of different clusters14 that can act as quantum dots15 and can be regarded as a bridge between molecular aggregates and bulk chalcogenide materials.16 We have chosen In(SAr)3 (Ar = phenyl, Ph, or p-tolyl, p-tol) as a building block for the synthesis of coordination polymers. Tuck and co-workers have established the synthesis of In(SAr)3 and explored the basic coordination chemistry of these thiolates.17 Others have shown the usefulness of indium thiolates as building blocks of precursors for chemical vapor deposition.18 In contrast to other, more commonly used thiolates, such as Cd(SAr)2 or Zn(SAr)2,19 In(SAr)3 possesses a much greater solubility in common solvents and shows less © XXXX American Chemical Society

tendency to form extended aggregates through bridging sulfur atoms. A recent work by Huang has explored the feasibility of using In(SAr)3 as a building block in polypyridyl-based coordination polymers with simple linear connectors such as 4,4′-bipyridine.20 Here, we present two different approaches to the use of In(SAr)3 as a building block, namely, the combination with 2,4,6-tris(4-pyridyl)triazine (tpt, Scheme 1, left), a trigonal ligand, to generate [(In(SPh)3)3(tpt)2] (1), an intricate 3D coordination polymer, and the combination with the chelating ligand 2-pyridinecarbaldehyde isonicotinoylhyScheme 1. Ligands 2,4,6-Tris(4-pyridyl)triazine (tpt, Left) and 2-Pyridinecarbaldehyde Isonicotinoylhydrazone (2HPCIH, Right)

Received: November 24, 2012 Revised: February 13, 2013

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dx.doi.org/10.1021/cg301724v | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Table 1. Basic Crystallographic Data for 1, 1a, 2, and 3 compound

1

1a

2

3

empirical formula formula weight (g·mol−1) crystal color and shape crystal size (mm3) crystal system space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z ρcalc (g·cm−3) μ(MoKα) (mm−1) absorption correction type min/max transmission θ range (deg) No. of measured reflections No. of independent reflections R(int) No. of indep. reflections (I > 2σ(I)) No. of parameters R1 (I > 2θ(I)) wR2 (all data) S (all data) Flack parameter Δρmax, Δρmin (e·Å−3)

C30H23InN4S3 650.52 yellow, block 0.2 × 0.06 × 0.05 cubic I432 22.375(2)

C19H12.67Cl3InN6.33 550.92 yellow, block 0.3 × 0.17 × 0.1 cubic I23 22.086(2)

C24H19InN4OS2 558.37 yellow, plate 0.15 × 0.07 × 0.02 orthorhombic P212121 10.283(3) 13.703(3) 16.698(4)

11201.8 (17) 12 1.157 0.82 numerical 0.874, 0.973 2.57−25.00 23161 1615 0.176 1652 100 0.086 0.220 1.02 0.15(14) 0.88, −1.51

10773.4 (17) 6 0.509 0.45 numerical 0.899, 0.960 1.30−24.96 66496 3023 0.149 1207 58 0.081 0.224 1.01 0.16(13) 0.27, −0.18

2352.9(10) 4 1.576 1.21 Gaussian 0.837, 0.964 1.92−26.71 33309 4975 0.184 3853 289 0.045 0.083 1.00 −0.03(3) 0.94, −1.04

C27.5H30InN4O3S2 643.49 yellow, block 0.27× 0.16 × 0.09 monoclinic P21/c 10.922(2) 13.515(3) 22.180(3) 119.18(3) 2858.5(9) 4 1.495 1.00 Gaussian 0.791, 0.917 1.84−26.73 39743 6031 0.082 5180 378 0.027 0.072 1.01

chloroform and methanol, and drying in air. Elemental analysis (calculated for a CHCl3 solvate with the overall formula [(In(SPh)3)3(tpt)2]·2.4CHCl3); the take-up of some CHCl3 molecules during the washing procedure was confirmed by TGA analyses, see the Supporting Information): Calcd for C30.8H23.8Cl2.4InN4S3 (found), %C 49.5 (49.9), %H 3.2 (3.3), %N 7.5 (7.4), %S 12.9 (13.0). Synthesis of [(InCl3)3(tpt)2] (1a). A saturated solution of tpt in 10 mL chloroform (resulting in a concentration of ca. 1 mg/mL) is layered with 5 mL of mesitylene. As a third phase, a solution of 11 mg of InCl3 in 5 mL of methanol is layered on top. After one day, colorless block crystals grow within the mesitylene phase and can be isolated by decanting, washing with chloroform and methanol, and drying in air. Yields for this model compound were not optimized. Elemental analysis (normalized to a solvent free formula [(InCl3)3(tpt)2] based on the invariant N content, as the CHN analyses indicated a variation of the CHCl3 content between 6 and 12 molecules per formula unit upon the washing procedure; the take-up of CHCl3 molecules was confirmed by TGA analyses, see the Supporting Information): Calcd for C12H8Cl3InN4 (found), %C 33.6 (33.9), %H 1.9 (1.7), %N 13.1 (13.1). Synthesis of [(In(SPh)2)(2-PCIH)] (2). Ten milligrams of (In(SPh)3 (0.02 mmol, 1 equiv) and 5 mg of 2-HPCIH (0.02 mmol, 1 equiv) are dissolved in 10 mL of methanol to form a bright yellow solution. Almost immediately the precipitation of a yellow powder sets in. The powder is filtered off, and the resulting clear solution left for crystallization by slow evaporation. After three days, very small crystals of 2 form at the bottom of the vessel, which can be isolated at 70% yield by decanting the remaining solution and washing with toluene and hexane to remove Ph2S2. Elemental analysis (consistent with the TGA analysis, see the Supporting Information): Calcd for C24H19InN4OS2 (found), %C 51.6 (54.0), %H 3.4 (3.6), %N 10.0 (10.9), %S 11.5 (11.9). Synthesis of [(In(S(p-tol))2)(2-PCIH)]·1.5MeOH·0.5H2O (3). Eleven milligrams of (In(S(p-tol))3) (0.02 mmol, 1 equiv) and 5 mg of 2HPCIH (0.02 mmol, 1 equiv) are dissolved in 10 mL of methanol to form a bright yellow solution. The solution is filtered to remove any

drazone (2-HPCIH, Scheme 1, right), which possesses an acidic proton capable of splitting off one of the thiolate ligands to form [(In(SPh)2)(2-PCIH)] (2) and [(In(S(p-tol))2)(2PCIH)]·2MeOH (3). The crystal structure of compound 1 is affected by systematic superstructure problems that were confirmed by means of transmission electron microscopy (TEM). To further aid in structure elucidation, the model compound [(InCl3)3(tpt)2] (1a) was prepared and crystallographically characterized. Compounds 2 and 3 represent seemingly similar coordination polymers that display a striking difference in their crystal structures due to the influence of the methyl group of the thiolate ligand. Compound 2 crystallizes in the chiral space group P212121 with only one handedness of the helical polymers in each crystallite and hence shows a second harmonic generation (SHG) effect, while 3 crystallizes in the centrosymmetric space group P21/c, accordingly comprising helices of both handednesses.

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1.07, −0.83

EXPERIMENTAL SECTION

General. All chemicals were used as received from commercial sources. In(SPh)3 and In(S(p-tol))3 were prepared according to the method described by Tuck.17a The ligands tpt21 and 2-HPCIH22 were also prepared according to the respective literature procedures. Thermogravimetric analyses (TGA, see Supporting Information, Figures S2−S5) were carried out on a NETZSCH STA 409 C/CD under a flowing argon atmosphere with a flow rate of 40 mL·min−1. Elemental analyses (C, H, N, and S) were performed on a Vario Micro cube. Synthesis of [(In(SPh)3)3(tpt)2] (1). A saturated solution of tpt in 10 mL chloroform (resulting in a concentration of ca. 1 mg/mL) is layered with a filtered solution of 40 mg of In(SPh)3 in 10 mL of methanol. After one day, light yellow block crystals start to grow at the phase border and continue to grow for several days. The crystals can be isolated at 75% yield by decanting the solution, washing with B



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refined on disordered positions using a DFIX restraint for the In1−Cl2 bond length (2.400(7) Å). The obtained structure model reveals a 3D metal−organic network with large voids, apparently occupied by highly disordered solvent molecules. The application of SQUEEZE23 allowed to improve the structure model parameters significantly, which showed that this part of structure has a large influence on the X-ray diffraction data. A combination of EADP/ISOR23 restraints had to be used for the organic part. Moreover, the whole organic ligand occupancy was refined in accordance with a defect network assumption to result in a refined overall occupancy factor of 0.79(1). On the final difference Fourier map, the highest maximum of 0.27 e/Å3 was observed at 0.14 Å from In1. For 1, the X-ray data could be also indexed in a cubic I-centered cell, with a = 22.375(2) Å. However, additional weak reflections are observed that accord with an I-centered cubic supercell with a = 44.750(2) Å. This phenomenon persists at room temperature and on cooling of the crystal down to 100(2) K as well as on cutting the crystals along different directions. A DSC diagram recorded for 1 does not show any signs of phase transitions. The symmetry of the diffraction pattern was consistent with both Laue groups m3̅ and m3̅m (Table S1, Supporting Information). For a first approach, the X-ray data were integrated in the small cubic cell, ignoring the weak reflections. For the initial structure refinement of 1 in the space group I23, the Cl atoms of 1a were simply replaced by S atoms. On further refinement cycles, the best parameters were afforded for the assumption of two S atom disorder components under application of a DFIX23 restraint for the In−S bond length (2.400(6) Å, similar to the range of 2.448(3)−2.455(3) Å in [In(SPh)3py2])25 and the introduction of a corresponding phenyl ring disorder model with soft DFIX restraints for the S−C bonds (1.6(1) Å), the In···C distances (3.5(1) Å), and the S···C distances (2.6(1) Å). A combination of EADP/ISOR restraints was also used. An attempt to refine the overall occupancy of the triazine ligand did not lead to significant discrepancies with respect to full occupancy. The structure model in I23 was then switched to a higher-symmetry model in I423, with only half of the triazine ligand being symmetry-independent. Phenyl rings showed also disorder here. Spurious electron density arising from the heavily disordered solvent molecules in the structural voids was treated with SQUEEZE. On the final difference Fourier map, the highest maximum of 0.88 e/Å3 was located at 0.33 Å from In1. The heavy atom positions of the original solution for 1 were then transformed to create an initial model for refinement in the 2 × 2 × 2 cubic supercell (1′, Figure S1, Supporting Information). Essentially, general features of the small subcell model could be reproduced, with a 3D network constituted by organic ligands and disorder of the S atoms bonded to In. Although the superstructure effect might arise from the features of the organic part, it was not possible to solve the problems this way, due to difficulties involved with intensity measurements for the weak reflections and due to reflection overlaps. For this reason, we will only discuss the average structure model (1) without providing structural parameters. Details of the Structure Solution and Refinement for Compound 2. All atoms were refined using anisotropic displacement parameters. On the final difference Fourier map, the highest maximum of 0.94 e/ Å3 was found at 1.12 Å from In1. Details of the Structure Solution and Refinement for Compound 3. Two sites occupied by disordered solvent molecules were found. In the first site, the presence of three methanol molecules was assumed with occupancies refined to 0.46(1), 0.32(2), and 0.22(2), respectively, restrained to add to unity by means of the SUMP23 restraint. Maxima located in the second site were interpreted as water and methanol molecules. One methanol and three water molecules were found. Cooperative disorder was assumed, the occupancies were refined and then fixed at refined values of 0.5, 0.3, 0.1, and 0.1, respectively. On the final difference Fourier map, the highest maximum of 1.07 e/Å3 was found at 0.91 Å from In1. Transmission Electron Diffraction. The investigations were performed using a Jeol JEM-3010 transmission electron microscope. Preparation of the sample has been achieved by grinding the crystals between microscope slides to produce thin enough fragments that are

insoluble residues and left for slow evaporation. After three days, yellow block crystals of 3 form at the bottom of the vessel, which can be isolated at 98% yield by decanting the remaining solution and washing with toluene to remove (p-tol)2S2. Elemental analysis (consistent with the TGA analysis, see the Supporting Information): Calcd for C27.5H30InN4O3S2 (found), %C 51.3 (51.94), %H 4.7 (4.03), %N 8.7 (8.38), %S 10.0 (11.49). Single-Crystal X-ray Diffraction. X-ray diffraction data were collected on a diffractometer equipped with a STOE imaging plate detector system IPDS2, using graphite-monochromated MoKα radiation (λ = 0.71073 Å) at 100 K. Structure solution and refinement were performed by direct methods and full-matrix least-squares on F2, respectively, using ShelxTL software.23 Table 1 summarizes the crystallographic data for 1, 1a, 2, and 3. Where possible, H atoms were placed in their calculated positions and constrained, applying a riding model with Ueq = 1.5/1.2Ueq(parent atom). Particular structural problems had to be faced in the case of 1, as described below. Further details on the structure solution and refinement are provided in the Supporting Information. Selected structural parameters for 2 and 3 are provided in Table 2.

Table 2. Selected Geometric Parameters for 2 and 3 [Å, deg] compound 2 In1O1 In1N3 In1S1 O1In1N3 O1In1S1 N3In1S1 O1In1N1i N3In1N1i S1In1N1i O1In1S2 symmetry codes: (i)

2.214 (4) In1N1i 2.273 (4) In1S2 2.4386 (16) In1N2 70.34 (16) S1In1S2 105.74 (12) N1iIn1S2 111.94 (12) O1In1N2 78.31 (14) N3In1N2 148.63 (18) S1In1N2 77.31 (13) N1iIn1N2 103.41 (12) S2In1N2 −x + 2, y − 1/2, −z + 3/2 compound 3

2.462 (6) 2.4647 (17) 2.468 (5) 141.05 (5) 83.97 (12) 138.21 (12) 67.93 (15) 87.93 (11) 143.45 (15) 87.25 (11)

In1O1 In1N2 In1S2 O1In1N2 O1In1S2 N2In1S2 O1In1N1 N2In1N1 S2In1N1 O1In1S1 N2In1S1 symmetry codes: (i)

2.2052 (16) 2.2737 (17) 2.4443 (11) 69.56 (6) 108.08 (5) 114.45 (5) 137.86 (6) 68.33 (6) 88.11 (5) 104.11 (5) 102.06 (5) −x + 1, y + 1/2,

2.4472 (19) 2.4623 (10) 2.4824 (18) 137.67 (3) 86.04 (5) 76.77 (6) 146.03 (6) 79.86 (5) 145.30 (6) 81.55 (5)

In1N1 In1S1 In1N3i S2In1S1 N1In1S1 O1In1N3i N2In1N3i S2In1N3i N1In1N3i S1In1N3i −z + 3/2

Details of the Structure Solution and Refinement for Compound 1. Both 1 and 1a form polyhedral crystals that seem to be optically isotropic when being examined under a polarizing microscope. EDX analyses confirmed the high amount of interstitial solvent (chloroform), which easily leaves the crystals when they are not covered with inert oil. In order to overcome the structural problems that are accompanied with the X-ray diffraction studies of 1 (see below), 1a was formed as an InCl3 adduct, the structure of which was solved and refined at first. For 1a, the X-ray data could be successfully indexed in a cubic Icentered cell, with a = 22.086(2) Å. The distribution of the reflection intensities allowed us to determine Laue symmetry m3̅ and the space group I23, with one In atom occupying the 12e Wyckoff position. The presence of a defect network had to be assumed, with statistically occupied atomic sites. Thus, on further refinement stages, the occupancy of the In1 atom site on the 12e special position was decreased to 0.25. Three Cl ligands that are bonded to the In atom, such as in the adduct [InCl3{HN(CH2Ph)2}2], for instance,24 were C



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Figure 1. Experimental ⟨155⟩ zone axis transmission electron diffraction pattern (center) with an overlay of the simulated diffraction intensity (purple disks) for structure 1 (left) and the 2 × 2 × 2 super structure (right). The brightness of the disks corresponds to the expected intensities and matches the experimental pattern. A few weak superstructure reflections can be observed (indicated with red arrows). transparent in the TEM, dispersing the powder in chloroform, and dipping a carbon-coated copper grid into the colloid. It was then sputter-coated with a thin Au film and cooled with liquid nitrogen during the measurements to reduce the rapid degradation of the material under electron irradiation. The highest available acceleration voltage of 300 kV has been chosen, due to its favorable influence on the stability of the crystal, similar to the behavior of other weakly interconnected organic crystals.26a Figure 1 depicts the experimental transmission electron diffraction pattern (center), which has been determined to be ⟨155⟩ zone axis by spot pattern indexing via the commercial java version of the EMS software26b and an overlay of simulated patterns for this zone axis for structure 1 (left side) and the 2 × 2 × 2 superstructure (right side). A few weak supercell reflections (arrows) can also be observed in electron diffraction, hinting toward the existence of the 2 × 2 × 2 superstructure. The weakness of the superstructure reflections compared to the simulation might be connected either with the rapid loss of crystallinity of the organic material upon electron bombardment or with partial loss of solvent during TEM sample preparation. Spectroscopy. To demonstrate an SHG effect for compound 2, the sample was illuminated using a diode-pumped Nd:YAG microchip laser emitting 5 ps pulses at a center wavelength of 1064 nm. Its fibercoupled output was collimated and then focused onto the crystals using an infinity-corrected 0.65 NA microscope lens. The laser power was controlled using a reflective filter wheel to minimize beam distortion and pointing uncertainties. The samples themselves were mounted on a thin metal slab attached to a 3D micropositioning stage yielding a spatial repeatability below 200 nm. The SHG at 532 nm generated in the sample was collected in transmission geometry using a similar objective lens and then imaged onto a 15 cm grating spectrometer equipped with a 300 l/mm grating in order to discriminate the transmitted fundamental. The signal was detected using a liquid-nitrogen-cooled charge-coupled device camera and readout using a PC.

Scheme 2. Synthesis Route for the Generation of Compounds 2 and 3, Given for the Use of In(SPh)3 (2); for the Synthesis of 3, In(S(p-tol))3 Was Reacted Instead

be solved and refined in the cubic space group I23 (Nr. 197). The resulting structure consists of eight interpenetrating 103-srs nets (vertex symbol 105·105·105) built from tpt ligands, which coordinate in a linear fashion to In(SPh)3 units. As this type of linear coordination of pyridyl ligands to In(SPh)3 moieties is the same as in In(SPh)3(pyridine)2,25 one might view the structure of 1 as a 3D extension of the basic building block, which is driven by the triangular architecture of the tpt ligand. The connecting mode is shown in Figure 2, a topological view

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DISCUSSION Compound 1 can be obtained by layering a chloroform solution of tpt with a methanolic solution of In(SPh)3. After one day, well-formed yellow block crystals can be observed at the phase border, that continue to grow for several days. Compounds 2 and 3 can be synthesized by mixing In(SPh)3 or In(S(p-tol))3 with equimolar amounts of 2-HPCIH in methanol to form yellow solutions, which give 2 or 3 upon slow evaporation. ArSH forms as a second product of the reaction and is readily oxidized in air to Ar2S2, which can be removed by washing the product with toluene and hexane. The reaction scheme for the formation of 2 and 3 is given in Scheme 2. The crystal structure solution and refinement of compound 1 is nontrivial as described in the Experimental Section and the Supporting Information. As a working model, the structure can

Figure 2. Coordination mode of In(SPh)3 units in 1 by two tpt ligands. Hydrogen atoms and disorder of thiolate ligands are omitted for clarity.

of a single and all eight nets is illustrated in Figure 3. The thiolate ligands on the indium atoms show severe disorder in this structure model. This also prohibits an accurate calculation of the void space within the structure, but it can be estimated to be around 20% of the overall volume.27 The nature and amount of solvent contained within these voids is highly dependent on sample treating conditions but can be estimated from EDX and elemental analysis data, resulting in an overall sum formula of [(In(SPh)3)3(tpt)2]·2.4CHCl3 for samples dried in air. The D



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Figure 3. Topological view of a single (left) and the eight interpenetrating 103-srs nets (right) in compound 1.

Figure 4. Topological illustration of the void volume described by the eight nets in 1.

Figure 5. Molecular structure of 2: thermal ellipsoid plot (30% probability, left) and illustration of the coordination environment of the indium atom (right).

space enclosed by the eight 103-srs nets can be topologically described as a tessellation of space with β-cages, as shown in Figure 4. 103-srs nets such as found in 1 and in the related compound 1a (see Experimental Section) are well-known in the chemistry of coordination polymers,28 and a number of interesting examples have been reported in the last years.29 Yet, compounds 1 and 1a represent examples of a nearly linear connection between the three-connecting nodes of a 103-srs net. This results in comparatively large pore sizes in each single net and thus enforces a high degree of interpenetration for network stabilization. Future work will address this by incorporating according guest molecules or by using larger terminal ligands at the indium atoms to reduce the degree of interpenetration. Compound 2 crystallizes in the non-centrosymmetric space group P212121 (No. 19). The molecular structure, shown in

Figure 5 (left side), consists of [(In(SPh)2)(2-PCIH)] units. The highly distorted coordination environment of the indium atom is shown in Figure 5 (right side). The oxygen as well as the 2-pyridyl and hydrazone nitrogen atoms of the ligand coordinate in a chelating fashion, while the 4-pyridyl nitrogen atom provides a connection between the single [(In(SPh)2)(2PCIH)] units, enabling the formation of helical chains (Figure 6, top) that run along the crystallographic b direction. The helicity is primarily defined by the aromatic rings of the thiolate 2-PCIH ligands, as demonstrated in Figure 6 (center), with a pitch of 13.703(3) Å, equivalent to b. The packing of these helices is very efficient, as shown in Figure 6 (bottom); hence, no additional solvent molecules are found within the structure. Interestingly, 2 does not crystallize as a racemic twin, but as a conglomerate of crystals that each contain only helices of one handedness. This can also be demonstrated via detection of an SHG effect (see below) on individual crystallites. E



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the product. Compound 3 crystallizes in the centrosymmetric space group P21/c (No. 14), and it is also composed of helical chains, as depicted in Figure 7 (left side). The asymmetric unit and the indium coordination environment in the two compounds is very similar (Table 2), as is the helical chain conformation, with a pitch of 13.515(3) Å. The main difference lies in the conformation of the thiolate ligands, shown as a comparison in Figure 7 (center and right side). This causes a decidedly different packing of the helices in 3: here, helices of different handedness are much more loosely packed than in 2, resulting in a 20% larger overall cell volume and accommodating two solvent molecules per formula unit (Figure 8).

Figure 8. Packing of the helices in 3 (different colors indicate different handedness, top) and positions of the solvent molecules in 3, depicted as a space-filling model within the topological representation of the helices (bottom).

Figure 6. Helical chains in the crystal structure of 2: view of a chain section to visualize the connection mode of In(SPh)2 units by the tetradentate 2-PCIH ligands (top), illustration of the helicity of the chains in 2, as defined by the aromatic rings of the ligands (center), and packing of the helices in 2, viewed down the crystallographic b axis (bottom).

The helical arrangement of the polymer chains in compounds 2 and 3 adds another example to the growing family of helical coordination polymers.30 The influence of small changes in the ligand composition and sterical demand on the supermolecular architectures of the title compounds is

The use of In(S(p-tol))3 instead of In(SPh)3 does not affect the coordination of the In atoms by 2-PCIH ligands in general, but has an obvious impact on the overall crystal structures of

Figure 7. Helical chains in the crystal structure of 3: view of a chain section to visualize the connection mode of In(S(p-tol))2 units by the tetradentate 2-PCIH ligands (left) and comparison of the chain conformation in 2 (center) and 3 (right). F



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Author Contributions

demonstrated in the different packing of the helices and the resulting overall structure. Single-Crystal Second Harmonic Generation Results for 2. The crystal structure of 2 discussed in the previous section suggests the possibility for second-harmonic generation (SHG). This process was studied for individual crystallites using a 1064 nm pulsed picosecond laser and a clear quadratic dependence of the 532 nm emission from the sample was observed as expected for this optical nonlinearity (Figure 9).

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding

German Science foundation (DFG) within DE 758/11-2 and within the framework of GRK1782. Notes

The authors declare no competing financial interest.

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Figure 9. Typical quadratic power dependence of the SHG intensity. The measured data are shown as squares. The solid line is a quadratic fit. The inset shows the narrow-band SHG emission spectrum.

Thus, 2 shows the potential to convert near-infrared light into the visible spectral range. The crystals on which the SHG measurements were performed were irregularly shaped with a maximum diameter of 0.15 mm. Hence, a comparison with established SHG materials regarding the strength of the nonlinear effect is difficult. Yet, the fact that we obtained an SHG signal is a further indication for the lack of a symmetry center in the structure of compound 2.

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CONCLUSIONS Different approaches to the employment of In(SAr)x (Ar = phenyl or p-tolyl) as a building block in extended hybrid coordination polymers have been successful by the formation of an intricate 3D coordination polymer with 2,4,6-tris(4-pyridyl)triazine (tpt) ligands attached to In(SPh)3 units and two helical polymers with tpt or 2-pyridinecarbaldehyde isonicotinoylhydrazone (2-HPCIH) ligands bridging between In(SAr)2 moieties. It showed that the slight change of the thiolate ligand from phenyl to p-tolyl has a significant impact on the crystal packing of the helices, allowing for the observation of an enantiopure species with second harmonic generation (SHG) properties.

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ASSOCIATED CONTENT

* Supporting Information S

EDX and TGA results. Additional details on crystal structure solution and refinement. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

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In(SAr)3 As a Building Block for 3D and Helical Coordination Polymers

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