Syntheses and Properties of Gold–Organotin Sulfide Clusters

Sep 1, 2017 - Ternary gold−organotin phosphane complexes, [(R1Sn)2(AuPMe3)2S4] (1) and [(R2Sn)2(AuPMe3)2S4] [2; R2 = CMe2CH2C(NNH2)Me], were synthes...
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Syntheses and Properties of Gold−Organotin Sulfide Clusters Eike Dornsiepen,† Jens P. Eußner,† Nils W. Rosemann,‡ Sangam Chatterjee,‡ and Stefanie Dehnen*,† †

Fachbereich Chemie and Wissenschaftliches Zentrum für Materialwissenschaften, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany ‡ Institute of Experimental Physics I, Justus-Liebig-University Gießen, Heinrich-Buff-Ring 16, D-35392 Gießen, Germany S Supporting Information *

ABSTRACT: We report that reactions of the binary organotin sulfide cluster [(R1Sn)3S4]Cl [A; R1 = CMe2CH2C(O)Me] with gold(I) phosphane complexes yield discrete ternary complexes [(R1Sn)2(AuPMe3)2S4] (1) and [(R2Sn)2(AuPMe3)2S4] [2; R2 = CMe2CH2C(NNH2)Me], which are related to recently published complexes [(R1,2Sn)2(AuPPh3)2S4] (B and C). Further, we present a binary tin sulfide cluster that cocrystallizes with a structuredirecting salt of a gold phosphane complex in [Au(dppe)2][(R3Sn)4S6Cl] [3; R3 = CMe2CH2C(NNHPh)Me]. The nature of the product depends on the choice of the phosphane ligand as well as the addition of hydrazine hydrate or phenylhydrazine. Additionally, we report on the photophysical properties of 1, 2, B, and C, which indicate that the different phosphane ligands only have a slight influence on the optical responses. The structure, however, has a significant impact on the luminescence efficiency.



[(R1Sn)2(AuPPh3)2S4] (B) and [(R2Sn)2(AuPPh3)2S4] (C), were obtained (Scheme 1). Herein, we report a series of new complexes prepared by reaction of the binary cluster A with different gold(I) phosphane complexes. Depending on the choice of the phosphane ligand, compounds [(R1Sn)2(AuPMe3)2S4] (1), [(R2Sn)2(AuPMe3)2S4] (2; R2 = CMe2CH2C(NNH2)Me), and [Au(dppe)2][(R3Sn)4S6Cl] [3; dppe = 1,2-bis(diphenylphosphino)ethane] were obtained (see Scheme 2). All reactions were carried out by dissolving A, gold(I) chloride, and the respective phosphane ligand in CH2Cl2, followed by the addition of (Me3Si)2S as the sulfide source.

INTRODUCTION During the last decades, a large variety of chalcogenidometallate compounds have been prepared and investigated. These are of interest mostly because of their easily tunable optoelectronic and semiconducting properties.1−3 The formal attachment of organic moieties to chalcogenidometallates yields neutral metal chalcogenide clusters, which have been investigated especially for chalcogenide clusters of the coinage metals,4 as well as clusters involving group 14 (i.e., tetrel) atoms.5 In recent years, functional organic ligands have been introduced to the clusters, allowing for further derivatization of the ligand shell.6 The organic ligands of organotetrel chalcogenide clusters of the general composition [(R1T)xEy] (T = Ge, Sn; E = S, Se, Te) comprise a keto function, which can be reacted with hydrazine derivatives.7 Reactions of binary clusters, like [(R1Sn)3S4]Cl [A; R1 = CMe2CH2C(O)Me], with transitionmetal complexes yield ternary clusters, with recent examples being [(R2Ge)4Pd6S12],8 [R42(SnS2Cu{PPh2Me})4] (R4 = [CMe2CH2C(NNH)Me]2),9 or [(R5Sn)4(ZnX)4S8] (R5 = CMe2CH2C[NNC(2-py)2]Me; X = Cl, Br, I).10 Recently, we reported a series of compounds with ternary M/Sn/S (M = Cu, Ag, Au) cores, among them the first crystallographically characterized ternary silver−tin and gold− tin sulfide complexes.11 The copper cluster [(R 1 Sn) 4 (SnCl) 2 (CuPPh 3 ) 2 S 8 ] and the silver cluster [(R1Sn)4(SnCl)2(AgPPh3)2S8] were found to be isomorphic, while the addition of hydrazine to the silver cluster leads to formation of the largest known cluster of this type, [(R2Sn)10Ag10S20]. In the case of gold, two complexes, © XXXX American Chemical Society



EXPERIMENTAL SECTION

General Procedures. All synthetic steps were carried out under exclusion of oxygen and moisture by use of standard Schlenk procedures because reactants and products are (moderately) air- and moisture-sensitive. [(R1Sn)3S4]Cl [A; R1 = CMe2CH2C(O)Me],7b (Me3Si)2S,12 and PMe313 were prepared according to literature procedures. Gold(I) chloride (ABCR), dppe (ABCR), phenyl hydrazine (Acros), and hydrazine hydrate (Merck) were used as received. 1H, 13C, 31P, and 119Sn NMR spectroscopy was carried out at 25 °C using Bruker DRX 300 MHz and DRX 500 MHz spectrometers. The chemical shifts are given in ppm relative to the residual protons of deuterated solvents for 1H NMR spectra and relative to the solvent signal for 13C NMR spectra. 13C, 31P, and 119Sn NMR spectra have been measured with 1H decoupling. Me4Sn was used as an internal standard in 119Sn NMR measurements. High-resolution mass Received: July 11, 2017

A

DOI: 10.1021/acs.inorgchem.7b01713 Inorg. Chem. XXXX, XXX, XXX−XXX

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Caution! Hydrazine and its derivatives, in the liquid and vapor form, are highly toxic. Contact of hydrazine with the human body and materials incompatible with hydrazine should be avoided. Deactivation of excess hydrazine hydrate with dilute(!) hydrogen peroxide is recommended. [(R1Sn)2(AuPMe3)2S4] (1). PMe3 (0.055 mL, 0.539 mmol) was added to a suspension of gold(I) chloride (0.168 g, 0.723 mmol) in CH2Cl2 (5 mL). To this was added a solution of A (0.102 g, 0.125 mmol) in CH2Cl2 (5 mL) and (Me3Si)2S (0.13 mL, 0.629 mmol), and the resulting green solution was stirred at room temperature for 26 h. After filtration, the solution was layered with hexane (10 mL). Colorless needles of 1 were obtained within 1 week. Yield: 18 mg (0.016 mmol, 9%). 1H NMR (300 MHz, CD2Cl2): δ 1.17 (s, 3 1 J( H−119Sn) = 120 Hz, CMe2, 12H), 1.62 (d, 2J(1H−31P) = 9.5 Hz, PMe3, 18H), 2.08 (s, Me, 6H), 2.65 (s, 3J(1H−119Sn) = 128 Hz, CH2, 4H). 31P NMR (101 MHz, CD2Cl2): δ −4.9. 119Sn NMR (122 MHz, CD2Cl2): δ 53.4 (d, 3J(119Sn−31P) = 38.9 Hz, 2J(119Sn−117Sn) = 170 Hz). IR: ν̃ = 2936 (w), 2914 (w), 2833 (m), 1693 (s), 1402 (w), 1360 (m), 1286 (w), 1244 (w), 1180 (m), 1121 (w), 957 (s), 858 (w), 746 (m), 681 (w), 610 (m), 445 (w) cm−1. ESI-MS. Calcd: m/z 1110.8829 ([M + H]+). Found: m/z 1110.8885. EDX (Au/P/S/Sn). Calcd: 0.50:0.50:1.00:0.50. Found: 0.48:0.49:1.00:0.52. [(R2Sn)2(AuPMe3)2S4] (2). PMe3 (0.03 mL, 0.291 mmol) was added to a suspension of gold(I) chloride (0.085 g, 0.366 mmol) in CH2Cl2 (5 mL). To this was added a solution of A (0.101 g, 0.124 mmol) in CH2Cl2 (5 mL) and (Me3Si)2S (0.07 mL, 0.332 mmol), and the resulting red solution was stirred at room temperature for 3.5 h. Hydrazine hydrate (0.03 mL, 0.618 mmol) was added, and stirring was continued for 40 min. The resulting suspension was filtered and the filtrate layered with hexane (10 mL). Colorless needles of 2 were obtained within 1 day. Yield: 50 mg (0.051 mmol, 27%). 1H NMR (300 MHz, CD2Cl2): δ 1.25 (s, 3J(1H−119Sn) = 130 Hz, CMe2, 12H), 1.71 (d, PMe3, 18H), 1.78 (s, Me, 6H), 2.48 (s, 3J(1H−119Sn) = 134 Hz, CH2, 4H), 5.05 (br s, NH, 4H). 13C NMR (75 MHz, CD2Cl2): δ 16.9 (d, PMe3), 26.0 (Me2), 26.6 (Me), 37.3 (SnC), 50.9 (CH2), 152.4 (CN). 31P NMR (101 MHz, CD2Cl2): δ −4.8. 119Sn NMR (187 MHz, CD2Cl2): δ −53.1 (d, 3J(119Sn−31P) = 37.3 Hz). IR: ν̃ 2851 (w), 2072 (m), 1426 (m), 1246 (m), 1104 (s), 808 (s), 767 (m), 730 (m), 693 (m), 651 (w), 613 (m), 481 (s) cm−1. EDX (Au/P/S/Sn). Calcd: 0.50:0.50:1.00:0.50. Found: 0.47:0.49:1.00:0.52. [Au(dppe)2][(R3Sn)4S6Cl] (3). Gold(I) chloride (0.043 g, 0.185 mmol) and dppe (0.037 g, 0.093 mmol) were dissolved in CH2Cl2 (3 mL), and a solution of A (0.050 g, 0.061 mmol) in CH2Cl2 (3 mL)

Scheme 1. Synthesis of Compounds B and C from A, along with Their Structural Diagrams11

spectrometry (HRMS; ESI = elctrospray ionization) spectra were acquired with a LTQ-FT Ultra mass spectrometer (Thermo Fischer Scientific). The resolution was set to 100.000. Energy-dispersive X-ray (EDX) spectroscopy was carried out on several crystals of each compound to verify the elemental composition found by X-ray diffraction (XRD) using a CamScan-4DV electron microscope at an acceleration voltage of 20 kV and a take off angle of 30°. Yields are based on the amount of Sn and refer to the amount of product isolated as single crystals. NMR spectra of the reaction mixtures indicate complex mixtures of various species, from which only the products with the lowest solubility are isolated by crystallization, which explains the relatively low yield.

Scheme 2. Synthesis of Compounds 1−3 from A, along with Their Structural Diagramsa

a

Details are provided in the Experimental Section and in the text below. B

DOI: 10.1021/acs.inorgchem.7b01713 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Crystallographic Data, Structure, and Refinement Results for Compounds 1−3 empirical formula fw/g·mol−1 cryst color and shape cryst size/mm3 cryst syst space group a/Å b/Å c/Å β/deg V/Å3 Z ρcalcd/g·cm−3 μ(Mo Kα)/mm−1 abs corrn type min/max transmn 2θ range/deg no. of measd reflns R(int) no. of indep reflns indep reflns [I > 2σ(I)] no. of param R1 [I > 2σ(I)]/wR2 (all data) S (all data) max peak/hole/e−·Å3 CCDC

1

2

3

C18H40Au2O2P2S4Sn2 1109.99 colorless plate 0.20 × 0.10 × 0.09 orthorhombic Pbca 14.7880(6) 11.8569(5) 17.8062(7) 90 3122.1(2) 4 2.361 11.334 multiscan 0.210/0.429 4.58−53.64 17667 0.0563 3302 2153 142 0.026/0.052 0.812 1.52/−1.02 1560505

C18H44Au2N4P2S4Sn2 1138.07 colorless plate 0.20 × 0.07 × 0.06 monoclinic P21/n 15.6147(4) 12.4310(4) 17.8723(5) 107.931(2) 3300.62(16) 4 2.290 10.723 numerical 0.276/0.545 3.04−53.60 24952 0.0602 6997 6050 313 0.020/0.038 1.021 1.32/−1.20 1560504

C100H112Au1Cl1N8P4S6Sn4 2449.40 colorless block 0.20 × 0.10 × 0.05 monoclinic P2/n 14.3260(5) 17.5405(10) 23.0901(9) 107.578(3) 5531.3(4) 2 1.471 2.452 multiscan 0.625/0.816 2.96−53.52 14817 0.1734 11711 5338 567 0.0737/0.1720 0.858 2.629/−0.977 1560506

was added. After the addition of (Me3Si)2S (0.033 g, 0.185 mmol), the rose-gold-colored solution was stirred at room temperature for 17 h. After filtration, phenyl hydrazine (0.030 g, 0.277 mmol) was added to the golden filtrate. After 45 min, the resulting suspension was filtered into a Schlenk tube and layered with hexane (6 mL). Colorless crystals of 3 were obtained within 1 day. Yield: 31 mg (0.013 mmol, 28%). 1H NMR (300 MHz, CD2Cl2): δ 1.01−1.07 (m, PCH2, 8H), 1.22 (s, Me2, 24H), 1.80 (s, Me, 12H), 2.64 (s, CH2, 8H), 6.52−6.59 (m, Hpara, 4H), 6.67−6.86 (m, Hpara, 6H), 7.06−7.31 (m, Harom, 48H). 13C NMR (75 MHz, CD2Cl2): δ 14.3 (Me2), 23.1 (Me), 31.5 (PCH2), 38.5 (CSn), 51.0 (CH2), 112.7, 115.9, 129.1, 129.3, 129.5, 131.0, 132.5, 132.7 (CAr), 133.2 (CN). 31P NMR (101 MHz, CD2Cl2): δ 20.4. IR: ν̃ 3191 (w), 3052 (w), 2931 (w), 2911 (w), 2848 (w), 1598 (m), 1494 (m), 1481 (m), 1458 (w), 1433 (m), 1410 (w), 1384 (w), 1366 (w), 1305 (w), 1248 (m), 1212 (m), 1142 (m), 1093 (m), 1068 (m), 1023 (w), 996 (w), 963 (w), 889 (w), 875 (w), 743 (s), 690 (s), 511 (s), 483 (s), 430 (w), 409 (w) cm−1. HRMS (ESI+). Calcd: m/z 993.2366 ([Au(dppe)2]+). Found: m/z 992.2340. HRMS (ESI−). Calcd: m/z 1122.9496 ([(R3Sn)3S4Cl2]−). found: m/z 1122.9504. A 119Sn NMR spectrum could not be obtained because of the low solubility of the compound. Single-Crystal Structure Analyses. Single crystals of compounds 1−3 were measured on a STOE imaging-plate detector system IPDS2 using Mo Kα radiation with graphite monochromatization (λ = 0.71073 Å) at 100 K. Reflection data were processed with X-Area 1.56.14 Structure solution was performed by direct methods and fullmatrix least-squares refinement against F2 using SHELXT15 and SHELXL-201316 software. Crystallographic data and details of the structure solution and refinement are provided in Table 1. Bond lengths and angles are summarized in Tables S1−S3. Hydrogen bonding in compounds 2 and 3 is depicted in Tables S4 and S5, respectively, and in Figures S1 and S2, respectively. Photophysical Properties Measurement. Linear absorption spectroscopy and photoluminescence (PL) measurements were performed on all three samples to investigate the influence of the different phosphane ligands and the structural modifications on the PL properties. The setup for absorption measurements is depicted in

Figure S3. A Hamamatsu deuterium lamp provides light in the ultraviolet (UV) range, and a standard tungsten halogen light bulb is used for the visible-to-near-IR spectral range. The light from the respective source is relayed onto the sample using aluminum-coated off-axis parabolic mirrors. A 1-mm-thick quartz window was used as a cover glass to ensure high transparency in the UV. A 45×-magnified image of the sample is formed by a 0.5 NA reflective microscope objective on a standard complementary metal oxide semiconductor camera, providing in situ optical control. Measurements of single crystals only were ensured by selecting a small fraction of the magnified sample image by placing a 50 μm pinhole in a complementary image plane of the objective. The light passing through the pinhole was collimated using an aluminum-coated off-axis parabolic mirror and focused onto the entrance slit of a Cherny− Turner-type spectrometer. The dispersed light was then detected using a thermoelectrically cooled back-deep-illuminated silicon chargecoupled-device camera. The PL setup is depicted in Figure S4. The 828 nm (1.5 eV) emission of a titanium−sapphire laser was frequency-tripled in order to provide above-band-gap excitation at 276 nm (4.5 eV). The 100 fs pulses were focused onto the sample mounted in a high-vacuum chamber to avoid UV-induced decomposition.17 Excitation and detection were performed in a confocal geometry using a 0.5 NA reflective microscope objective to avoid chromatic aberrations. PL is relayed onto the same detection setup as that used for the linear absorption measurements. To enhance residual excitation laser suppression and reduce stray light, a 3-mm-thick Schott WG280 color glass filter is placed in front of the spectrometer. Methods of the Quantum-Chemical Calculations. Optimized molecular structures and energies were obtained from density functional theory (DFT) calculations using TURBOMOLE 7.1.118 with the TPSSH functional.19 The molecular geometries were optimized with the def2-SVP basis set and the energies calculated using def2-TZVP.20 C

DOI: 10.1021/acs.inorgchem.7b01713 Inorg. Chem. XXXX, XXX, XXX−XXX

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RESULTS AND DISCUSSION Synthesis and Crystal Structures of 1 and 2. The reaction of A with gold(I) chloride, PMe3, and (Me3Si)2S in CH2Cl2 and subsequent layering of the reaction solution with hexane yielded colorless crystals of 1. Compound 1 crystallizes in the orthorhombic space group Pbca with four formula units per unit cell. The molecular structure consists of a central fourmembered [Sn2S2] ring, with both tin atoms bearing one organic ligand oriented to one side of the central ring and one SAuPMe3 unit oriented to the other half-space (see Figure 1).

The described similarities with the structure of the molecules in compound B indicate that replacement of the phosphane ligand does not notably influence the molecular structure of the complex, although Tolman’s cone angles22 are significantly different (118° for PMe3 vs 145° for PPh3), which usually affects cluster structures and sizes (for example, those of phosphane-decorated coinage metal chalcogenide clusters).23 We ascribe this observation to the fact that the phosphane ligands are bound at a rather exposed position, which provides enough space for phosphane ligands of a broad range of steric demands. In contrast, however, we see a distinct influence on the intermolecular interactions, which naturally allow for aurophilic interactions only in the presence of small (terminal) phosphane ligands. In situ derivatization of 1 by the addition of hydrazine hydrate to the reaction solution leads, after layering of the filtrate with hexane, to the formation of 2 as colorless needles. 2 crystallizes in the monoclinic space group P21/n. The molecular structure is related to that of 1 and also to the PPh3-terminated hydrazone complex C, although in a varied conformation. Unlike in 1, the [S−Au−P] fragments adopt a cis/cis geometry as in C, however positioning them on the same side of the central [Sn2S2] ring, where they point toward each other, which significantly discriminates the structure from the mode found in C. In this way, an intramolecular aurophilic interaction is found between the two gold atoms, with an Au1−Au2 distance of 3.2835(2) Å (see Figure 3). While most bond lengths and

Figure 1. Molecular structure of compound 1. Ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity.

The two SAuPMe3 units are located on opposite sides of the central ring. They adopt a trans/trans geometry, thus both pointing away from the [Sn2S2] moiety. The molecular structure of 1 is very similar to that of the recently published ternary complex B. The S1−Sn1−S2 angles are almost identical [110.41(6)° in 1 versus 110.22(9)° in B], while the Sn1−S1− Au1 angles differ slightly, with 91.63(5)° (1) versus 96.63(9)° (B). The Au1−S1 [2.3094(14) Å for 1 and 2.291(2) Å for B] and Au−P [2.2606(15) Å in 1 vs 2.260(2) Å in B] bonds are very similar to each other, as was observed in B. The central four-membered ring shows inversion symmetry with bond lengths of 2.4546(16) Å (Sn1−S2) and 2.4193(16) Å (Sn1i− S2) and bond angles near 90° [87.29(5)° for the Sn−S−Sn angle and 92.71(5)° for the S−Sn−S angle], all comparing well with the reported data for B [Sn1−S1 2.402(2) Å; Sn1i−S1 2.463(2) Å; Sn−S−Sn 86.30(7)°; S−Sn−S 93.70(7)°].11 One might discuss a very weak aurophilic interaction to be present between the gold atoms that come close along the crystallographic b axis (see Figure 2), with an Au−Au distance of 3.6413(5) Å. This value is beyond the typical range for aurophilic interactions of 2.50−3.50 Å21 but does show a structure-directing influence by stabilizing the isomer found here (see the DFT calculations below). Compound B, on the other hand, does not form any aurophilic interactions even far beyond this typical range because of the sterically more demanding PPh3 groups, which at the same time stabilize its conformation (see also below) .

Figure 3. Molecular structure of compound 2. Ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity.

angles in 2 and C do not differ significantly, the Sn1−S3−Au1 angle in 2 [99.31(3)°] is smaller than the corresponding angle in C [103.86(13)°], indicating bending of the [S−Au−P] fragments toward each other in order to form the aurophilic interaction.

Figure 2. Illustration of the intermolecular Au···Au interactions along the crystallographic b axis of compound 1. The style of representation and the color code are the same as those in Figure 1. D

DOI: 10.1021/acs.inorgchem.7b01713 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 4. Intermolecular hydrogen bonds within the crystal structure of compound 2 along the crystallographic a axis. The [S−Au−PMe3] moieties that are additionally bonded to the tin atoms are shown in a semitransparent mode for clarity. The style of representation and the color code are the same as those in Figure 3.

The central four-membered ring lacks inversion symmetry, reflected by the slightly varying Sn−S distances and bond angles. The angles between the central ring and the [S−Au−P] fragments are significantly larger as in 1 because of their different orientations [119.34(4)° for S3−Sn1−S1 and 120.92(3)° for S4−Sn2−S2]. The Au−S bonds are of similar length [2.3237(9) Å for Au1−S3 and 2.3113(9) Å for Au2− S4]. The same holds for the Au−P bonds [2.2527(10) Å for Au1−P1 and 2.2562(9) Å for Au2−P2]. The observation of aurophilic interactions in 2 versus no such interactions in C can again be ascribed to the lower steric demand of the PMe3 groups in 2 in comparison to the PPh3 groups in C. Furthermore, although the crystal structure of 2 does not exhibit intermolecular aurophilic interactions, it shows intermolecular connection of the clusters by hydrogen bonds. One hydrogen atom of each of the hydrazine groups (H1 and H3) forms one intramolecular and one intermolecular hydrogen bond to the sulfur atoms of the central fourmembered ring (S1 and S2, respectively), thus connecting the individual clusters into a chain along the crystallographic a axis (see Figure 4). The reason why 1 and 2 obviously favor different isomers is a subtle balance between intra- and intermolecular aurophilic interactions and these hydrogenbonding interactions (see also below). In the 119Sn NMR spectrum, compound 1 produces a shift of 53.4 ppm with a 3J coupling to the phosphorus-31 atom of 38.9 Hz. The 31P NMR spectrum shows a signal at −4.9 ppm. For compound 2, the 119Sn NMR shift undergoes a significant highfield shift to −53.1 ppm, while both the 3J(119Sn−31P) coupling (37.3 Hz) and the 31P chemical shift (−4.8 ppm) differ only slightly. The high-field shift in the 119Sn NMR spectra is consistent with the shift observed in other hydrazine-functionalized clusters7b,11 and can be attributed to the hydrazine ligand being a stronger σ donor than the keto ligand. Quantum-Chemical Investigation of Isomers. In order to elucidate the different structures of 1 and 2 observed within the crystal structures, quantum-chemical calculations of the molecular geometries were conducted using DFT methods. The structures of 1 (identical with B) and 2, as well as that of C, have been calculated for R1 and R2 and with PMe3 ligands at the gold atoms throughout (Figure 5). Remarkably, the geometry optimizations for 1 and CMe (denoted as CMe here to indicate the replacement of PPh3 groups in C with PMe3 groups) led to the same minimumenergy structure, which is the one found in the crystal structure of C. This indicates that the topology found for 1 is only viable when stabilized by intermolecular aurophilic interactions, which

Figure 5. Calculated molecular structures for type 1 (left) and 2 (right) topologies with R1 (top) and R2 (bottom), respectively, indicating the structures that correspond to the experimentally found or hypothetical ones of compounds 1 and 2. Hydrogen atoms are omitted for clarity. The color code is the same as that in Figures 1−4: Sn, turquoise; Au, orange; S, yellow; P, purple; O, red; N, blue; C, wires; H, not shown.

DFT calculations on a single molecule do not account for. During geometry optimization of B, on the other hand, the trans/trans geometry found in the crystal structure was retained. We attribute this to the higher steric demand of the PPh3 groups, the rotation of which toward the Sn2S2 core structure seems kinetically unfavorable. Because both isomers are indeed known to exist with PPh3 ligands (in compounds B and C), we assume, however, that both isomers form, with the one with a higher crystallization tendency obtained in crystalline form for each of the ligands R1 (B) or R2 (C). For compound 1, in contrast, the isomer related to B can easily rearrange into the one related to C because the PMe3 groups are less sterically hindered. Consequently, additional hindrance by Au···Au interactions is required to retain the trans/trans conformation. The energy differences of the calculated type 1 and 2 topologies are listed in Table 2. For both complexes, the observed type 1 structure is less stable than the type 2 topology (by 25.7 kJ·mol−1 for compound 1 and 23.9 kJ·mol−1 for compound 2), because the latter is stabilized by intramolecular aurophilic interactions. Thus, it is not comprehensible at first glance why the two compounds would adopt different molecular structures. E

DOI: 10.1021/acs.inorgchem.7b01713 Inorg. Chem. XXXX, XXX, XXX−XXX

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case of sterically more demanding ligands, another motif composed of two defect-heterocubane moieties bridged by two chalcogen atoms is the most common one.7a In both cases, the tetrel atoms bearing organic ligands are five-coordinate, which stabilizes the quoted architectures. Hence, the adamantane-like structure of 3 can be attributed to the fact that the NH groups of the hydrazone substituents prefer the formation of extramolecular interactions with the chloride anions of the gold complex over an intramolecular coordination of the tin atoms. Thus, all tin atoms remain four-coordinate, in which case the adamantane-like structure is indeed energetically favored.7a,26 The chloride anions are interacting with the N−H groups of two neighboring cluster molecules, generating chlorideconnected strands along the crystallographic a axis (see Figure 7). The cationic [Au(dppe)2]+ complexes are situated between those strands. At this point, the following question arises: why should a neutral cluster cocrystallize with an entire formula unit of the salt of a gold phosphane complex instead of crystallizing separately, albeit in another isomeric form? Because of the energetic preference of the five-coordinate tin atoms in the double-decker-type architecture, the adamantane-like cluster would presumably not be isolated without the cocrystallizing gold complex. However, we note that the structure-directing NH···Cl coordination seems to be energetically favored over the intramolecular N→Sn coordination, which would stabilize the double-decker-type cluster isomer. Another remarkable point is that the formation of hydrogen bonds between the chloride anion and the neutral cluster molecule seems to outperform a potential ionic interaction with the cationic complex, according to the distances found in the crystal structure: the Cl···Au distance is 8.753(5) Å, while the distance between the chloride anion and the geometric center of the adamantane-like cluster (defined as the center of the S1···S3 connecting line) is only 7.167 Å, indicating that the distances to the cluster atoms are even shorter. This suggests that one should consider the cluster not as an innocent filling material, comparable to a crystal solvent, but instead as a weak, H+terminated Lewis acid that forms an overall anionic complex with the chloride anion. This complex anion, which assembles into a polymer in the crystal (see Figure 7), is of steric demand similar to that of the bulky [Au(dppe)2]+ cation, thus

Table 2. Total Energies for the Topologies of Compounds 1 and 2 with Keto and Hydrazone Ligands, Respectively ligand 1

R

R2

topology

total energy/H

ΔE(observed−hypothetical)/kJ·mol−1

(obs) (hyp) (hyp) (obs)

−3836.759458 −3836.769254 −3907.691800 −3907.700890

+25.7

1 2 1 2

−23.9

However, because the calculations are performed for a single molecule, and hence do not account for the intermolecular Au···Au contacts, this result confirms our assumption that the intermolecular aurophilic interactions effectively stabilize the topology observed for 1. Because of the presence of hydrazine groups, compound 2 can establish intermolecular hydrogen bonds; hence, the intramolecular Au···Au contacts allow one to make use of both stabilizing effects at once. Synthesis and Crystal Structure of 3. The use of monodentate phosphane ligands like PPh3 and PMe3 yielded only tetranuclear ternary complexes so far, instead of clusters with larger inorganic cores. One way of stabilizing large inorganic cluster cores is the use of bidentate phosphane ligands, which enable the protection of a large cluster surface with relatively few ligands. Examples for which this concept has afforded enormously large cluster cores are [Ag262S100(StBu)62(dppb)6]24 and [Au18Se8(dppe)6]Cl2.25 We thus intended to transfer this concept to Au/Sn/S clusters. The reaction of A with gold(I) chloride, dppe, and (Me3Si)2S in CH2Cl2, the in situ addition of phenyl hydrazine to the reaction solution, and the subsequent layering of the filtrate with hexane yielded colorless crystals of compound 3. The compound crystallizes in the monoclinic crystal system in the space group P2/n with two formula units per unit cell. Within the crystal, one formula unit of the in-situ-formed complex [Au(dppe)2]Cl cocrystallizes with a tin sesquisulfide cluster of the composition [(R3Sn)4S6], as shown in Figure 6. The inorganic core of the [(R3Sn)4S6] cluster adopts an adamantane-like structure. This is remarkable because, for ligands containing σ-donor atoms that are capable of forming intramolecular Lewis acid−base adducts with the tetrel atoms, other structural motifs are energetically preferred and usually found: for tin sulfide clusters, this is usually a “double-decker”like structural isomer of the adamantane structure, or in the

Figure 6. Molecular structure of compound 3. Ellipsoids are drawn at 50% probability. F

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Figure 7. Packing diagram of compound 3, viewed (approximately) along [001]. The style of representation and the color code are the same as those in Figure 6.

promoting their crystallization. From this point of view, the cluster can be viewed as some kind of an anion-sequestering agent here. Photophysical Properties. Because gold chalcogenide complexes are known to show luminescence in the solid state,27 we were interested in exploring the optical absorption and luminescence properties of these types of multinary complexes comprising inorganic Sn/S/Au/P units. The studies were carried out on the PPh3-terminated complexes B and C, as well as on the PMe3 compounds 1 and 2. First, we carried out linear absorption measurements on individual single crystals to investigate the influence of the ligands and the structure. The resulting absorption spectra are shown in Figure 8. All compounds exhibit a pronounced absorption edge, with a plateau of maximum absorption reached at 3.3−3.7 eV, in

agreement with the colorless appearance of the single crystals. For compounds B and C, the onset of absorption occurs abruptly at ca. 3.0 eV (410 nm, B) and 3.3 eV (380 nm, C), respectively. Because these compounds do not differ in their structural features but only in the nature of the fifth ligand at the tin atoms, we ascribe the slightly different onset of absorption to this difference. Indeed, as shown for compound 1 below, in such kinds of complexes, the charge transfer mainly involves the S p orbitals (highest occupied molecular orbital, HOMO) and the keto versus hydrazine group (lowest unoccupied molecular orbital, LUMO). Because the LUMO level is lower in the case of the keto ligand, absorption in B occurs at slightly lower energies. The same, yet even more pronounced, trend is visible for compound 1 versus 2. However, in these cases, a sharp onset of absorption is not visible. Instead, the absorption increases smoothly between 1.9 eV (640 nm, 1) and 2.0 eV (620 nm, 2) and reaches the absorption maximum at ca. 3.7 eV (330 nm). To understand this significantly different course of the absorption curve, we inspected the frontier orbitals of 1 and 2. Figure 9 shows contour plots of the respective HOMOs and LUMOs. The different isomers possess different features in the frontier orbital region. Both HOMOs are dominated by contributions of the S 3p atomic orbitals (AOs), with larger contributions found at the sulfur ligands that bind to the gold atoms (that also contribute to a small extent). The LUMO, however, differs in that it is mainly concentrated at the keto group of the organic ligand in compound 1 (as in B and C; see above), while it is delocalized over the central Sn2S4 moiety in 2. This explains the notable bathochromic shift of the onset of absorption observed for compound 1, as the keto group is much more electronegative, in qualitative agreement with the smaller HOMO− LUMO gap calculated for 1 (3.6 vs 4.0 eV in 2).

Figure 8. Linear absorption spectra of individual single crystals of compounds B (black), C (blue), 1 (red), and 2 (green). The absorption above 3.26 eV (380 nm) was obtained using a deuterium lamp as the light source, while for energies below 3.26 eV, a tungsten halogen lamp was used. G

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Figure 10. PL spectra of compounds B (black), C (blue), 1 (red), and 2 (green). For better readability, the spectra of compounds 1 and 2 are magnified by a factor of 20.



CONCLUSIONS Reactions of the binary organotin sulfide cluster A with gold(I) phosphane complexes yield discrete ternary complexes 1 and 2 or a binary tinsulfide cluster, 3, in which a cocrystallizing gold complex has a structure-directing influence, depending on the choice of the phosphane ligand as well as the addition of hydrazine hydrate or phenylhydrazine, respectively. The structural similarities and differences of 1 and 2 and the related compounds B and C, all of which are based on an inorganic [Sn2S4Au2P2] moiety, were explained by the subtle influence of the involved phosphane ligands and organic groups, which allows for the formation of inter- or intramolecular aurophilic interactions, respectively, only in 1 and 2, and enables additional intermolecular hydrogen bonding in 2 only. Quantum-chemical studies support these assumptions, and they also serve to rationalize the experimentally observed photophysical properties of these four compounds.

Figure 9. Illustration of the frontier orbitals (HOMOs to the left and LUMOs to the right) of calculated compounds 1 (top) and 2 (bottom). Amplitudes are drawn at 0.03 au.

To comprehend the smooth increase of the absorption, however, one has to (additionally) consider the intermolecular interactions because these set both 1 and 2 apart from compounds B and C. We assume that the intermolecular Au··· Au contacts in 1 and the hydrogen-bonding network in 2 affect the charge transfer; in 1, the involved gold atoms contribute to the HOMO, while in 2, the sulfur atoms involved in the hydrogen bonds contribute to the LUMO. Because the interactions are weaker than covalent bonds, they most likely broaden the electronic absorption curve by soft vibrational modes. Another feature is observed for compound C as a sharp absorption peak on top of the absorption edge at 3.51 eV (353 nm). This additional peak may be attributed to the fact that only compound C crystallizes as a solvate, with five molecules of dichloromethane per formula unit, while the other three compounds crystallize solvent-free. It is well-known that the solvent, also known as the crystal solvent, affects the absorption behavior.28 As a next step, we performed PL measurements. On the basis of the absorption data discussed above and to ensure sufficient absorption, the excitation was set to 4.5 eV (276 nm). The resulting emission spectra are shown in Figure 10. In general, all compounds show a broad-band, unstructured luminescence. The PL spectra of the two triphenylphosphane complexes (B and C) possess maxima at 2.4 eV (515 nm), with C possessing the largest PL intensity, probably due to missing relaxation pathways within these mostly molecular solids. The maxima of the trimethylphosphane complexes (1 and 2) come along with much lower PL intensities (the lowest observed for compound 2) and exhibit a slight hypsochromic shift to 2.7 eV (460 nm), as expected based on the bathochromic shift of the absorption energies. We assume that the intermolecular interactions quench the PL properties of these compounds because nonradiative transitions are likely occurring between vibrational levels. Because compound 2 is the only one exhibiting two types of weak interactions (intramolecular aurophilic and intermolecular hydrogen-bonding interactions), we ascribe the more pronounced PL quench to this property.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01713. Bond lengths and angles of compounds 1−3, hydrogen bonding in compounds 2 and 3, linear absorption microscopy setup, and micro-PL setup (PDF) Accession Codes

CCDC 1560504−1560506 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.



AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: (+49) 6421 282 5751. ORCID

Nils W. Rosemann: 0000-0002-7663-0397 Stefanie Dehnen: 0000-0002-1325-9228 H

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

The authors declare no competing financial interest.



ACKNOWLEDGMENTS This work was supported by the Deutsche Forschungsgemeinschaft within the framework of GRK1782.



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