Synthesis, Characterization, Photophysical, and Theoretical Studies of

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Organometallics 2009, 28, 1369–1376

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Synthesis, Characterization, Photophysical, and Theoretical Studies of Supramolecular Gold(I)-Silver(I) Alkynyl-Phosphine Complexes Igor O. Koshevoy,*,† Antti J. Karttunen,† Sergey P. Tunik,*,‡ Matti Haukka,† Stanislav I. Selivanov,‡ Alexei S. Melnikov,# Pavel Yu. Serdobintsev,# and Tapani A. Pakkanen*,† Department of Chemistry, UniVersity of Joensuu, 80101, Joensuu, Finland, Department of Chemistry, St.-Petersburg State UniVersity, UniVersitetskii pr. 26, 198504, St.-Petersburg, Russian Federation, and Department of Physics, St.-Petersburg State UniVersity, UlijanoVskaja 3, 198504, St. Petersburg, Russian Federation ReceiVed October 17, 2008

The reactions of diphosphino-alkynyl gold complexes (PhC2Au)PPh2(C6H4)nPPh2(AuC2Ph) (n ) 1, 2, 3) with Ag+ lead to the formation of supramolecular heterometallic aggregates, which consist of the [AuxAgy(C2Ph)2x]y-x clusters (x ) (n+1)(n+2)/2; y ) n(n+1)) “wrapped” in gold-diphosphine “belts”. The composition of the “belts” depends on the size of the heterometallic cluster; for n ) 1 it is an open-loop tetrametallic diphosphine-alkynyl [Au(C2Ph)Au2Ag(PPh2(C6H4)2PPh2)3]3+ complex, and for n ) 2, 3 it is a symmetrical closed triangle [Au3{PPh2(C6H4)nPPh2}3]3+. The complex for n ) 1 was characterized crystallographically and spectrally; the larger ones (n ) 2, 3) were investigated in detail by NMR spectroscopy. Their luminescence behavior has been studied, and an intense room-temperature solution emission with maximum quantum yield of 0.35 (n ) 2) was detected. Computational studies have been performed to provide additional insight into the structural and electronic properties of these supramolecular complexes. Theoretical results obtained are in good agreement with the experimental data, supporting the proposed structural motif. These studies also suggest that the observed efficient long-wavelength luminescence is associated with transitions within the central Au(I)-Ag(I) heterometallic fragment. Introduction Current attention to the chemistry of group 11 metal alkynyl complexes has been stimulated by the discoveries of their manifold emissive properties1,2 and interesting structural topologies. The diverse coordination mode of the alkynyl moiety together with metallophilic interactions between coinage metal centers3 leads to the formation of clusters, multimetallic aggregates, or extended solid-state architectures.2,4,5 The structural motif and physical properties of these assemblies are * Corresponding authors. E-mail: [email protected]; tapani. [email protected]; [email protected]. † University of Joensuu. ‡ Department of Chemistry, St.-Petersburg State University. # Department of Physics, St.-Petersburg State University. (1) (a) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586–2617. (b) Yam, V. W.-W. Acc. Chem. Res. 2002, 35, 555–563. (c) Che, C.-M.; Chao, H.-Y.; Miskowski, V. M.; Li, Y.; Cheung, K.-K. J. Am. Chem. Soc. 2001, 123, 4985–4991. (d) Lu, W.; Zhu, N.; Che, C.-M. J. Am. Chem. Soc. 2003, 125, 16081–16088. (e) Ma, Y.; Che, C.-M.; Chao, H.Y.; Zhou, X.; Chan, W.-H.; Shen, J. AdV. Mater. 1999, 11, 852–857. (f) Lin, Y.-Y.; Lai, S.-W.; Che, C.-M.; Cheung, K.-K.; Zhou, Z.-Y. Organometallics 2002, 21, 2275–2282. (2) Koshevoy, I. O.; Karttunen, A. J.; Tunik, S. P.; Haukka, M.; Selivanov, S. I.; Melnikov, A. S.; Serdobintsev, P. Y.; Khodorkovskiy, M. A.; Pakkanen, T. A. Inorg. Chem. 2008, 47, 9478–9488. (3) (a) Pyykko, P. Chem. ReV. 1997, 97, 597–636. (b) Pyykko, P. Chem. Soc. ReV. 2008, 37, 1967–1997. (c) Schmidbaur, H.; Schier, A. Chem. Soc. ReV. 2008, 37, 1931–1951. (4) (a) McArdle, C. P.; Vittal, J. J.; Puddephatt, R. J. Angew. Chem., Int. Ed. 2000, 39, 3819–3822. (b) Yip, S.-K.; Cheng, E. C.-C.; Yuan, L.H.; Zhu, N.; Yam, V. W.-W. Angew. Chem., Int. Ed. 2004, 43, 4954–4957. (c) Zhao, L.; Wong, W.-Y.; Mak, T. C. W. Chem.-Eur. J. 2006, 12, 4865– 4872. (d) Chen, M.-L.; Xu, X.-F.; Cao, Z.-X.; Wang, Q.-M. Inorg. Chem. 2008, 47, 1877–1879. (e) Zhang, T.; Kong, J.; Hu, Y.; Meng, X.; Yin, H.; Hu, D.; Ji, C. Inorg. Chem. 2008, 47, 3144–3149.

evidently determined by the sterochemical properties of the ligands’ environment and nature of the metal centers that form a polynuclear framework. Thus, utilization of alkyne and ancillary phosphine ligands along with variation of the metals opens wide possibilities for the construction of multimetallic aggregates. In our recent studies we have demonstrated relatively simple and efficient self-assembly of the intensely luminescent Au(I)-Cu(I) alkynyl-diphosphine complexes upon treating the digold complexes (PhC2Au)PPh2(C6H4)nPPh2(AuC2Ph) (n ) 1, 2, 3) with Cu+.2,6 The clusters obtained possess from 6 to 25 metal atoms and display a similar structural pattern, the [AuxCuy(C2Ph)2x]y-x alkynyl clusters being “wrapped” in the [Au3(diphosphine)3]3+ triangles. It should be noted that the amount of reported Au(I)-Cu(I) and Au(I)-Ag(I) alkynylphosphine complexes to date is still very limited despite their attractive luminescent properties.2,5-8 This spurred our aim to further explore this chemistry, i.e., by searching for different structural topologies and modifying photophysical properties of this type of compounds via modification of the composition of the metal core. We intended to extend the described synthetic (5) Wei, Q.-H.; Zhang, L.-Y.; Yin, G.-Q.; Shi, L.-X.; Chen, Z.-N. J. Am. Chem. Soc. 2004, 126, 9940–9941. (6) Koshevoy, I. O.; Koskinen, L.; Haukka, M.; Tunik, S. P.; Serdobintsev, P. Y.; Melnikov, A. S.; Pakkanen, T. A. Angew. Chem., Int. Ed. 2008, 47, 3942–3945. (7) (a) Yam, V. W.-W.; Cheung, K.-L.; Cheng, E. C.-C.; Zhu, N.; Cheung, K.-K. Dalton Trans. 2003, 1830–1835. (b) Vicente, J.; Chicote, M.-T.; Alvarez-Falcon, M. M.; Jones, P. G. Organometallics 2005, 24, 4666–4675. (c) de la Riva, H.; Nieuwhuyzen, M.; Fierro, C. M.; Raithby, P. R.; Male, L.; Lagunas, M. C. Inorg. Chem. 2006, 45, 1418–1420. (d) Tang, H.-S.; Zhu, N.; Yam, V. W.-W. Organometallics 2007, 26, 22–25. (8) Wei, Q.-H.; Zhang, L.-Y.; Yin, G.-Q.; Shi, L.-X.; Chen, Z.-N. Organometallics 2005, 24, 3818–3820.

10.1021/om8010036 CCC: $40.75  2009 American Chemical Society Publication on Web 01/21/2009

1370 Organometallics, Vol. 28, No. 5, 2009

strategy in order to prepare and carry out photophysical and theoretical investigations of a family of novel Au(I)-Ag(I) alkynyl-phosphine clusters.

Experimental Section General Comments. (AuC2Ph)n,9 (AgC2Ph)n,10 and (PhC2Au)2(PPh2(C6H4)nPPh2) (n ) 1, 2, 3)2,6 were synthesized according to published procedures. Tetrahydrofuran was distilled over Nabenzophenoneketyl under a nitrogen atmosphere prior to use. Other reagents and solvents were used as received. Solution 1H, 13C, and 31 P NMR spectra were recorded on Bruker Avance 400 and Bruker DPX 300 spectrometers. Mass spectra were determined on a Bruker APEX-Qe ESI FT-ICR instrument, in the ESI+ mode. Microanalyses were carried out in the analytical laboratory of St.-Petersburg State University. UV-vis spectra were recorded on a Shimadzu UV 3600 spectrophotometer. [{Au3Ag2(C2Ph)6}Au3Ag(C2Ph)(PPh2C6H4PPh2)3][PF6]2 (1). (PhC2Au)2(PPh2C6H4PPh2) (174 mg, 0.167 mmol) was partially dissolved in THF (15 cm3) under a nitrogen atmosphere. Solid (AgC2Ph)n (12 mg, 0.057 mmol) was added followed by a solution of AgPF6 (28 mg, 0.111 mmol) in THF (4 cm3). The reaction mixture was stirred under nitrogen in the absence of light for 2 h to give a transparent yellow-greenish solution. It was evaporated to dryness, and the solid residue was recrystallized twice by evaporation of a CH2Cl2-toluene solution under moisture-free conditions at room temperature to give bright yellow-green blocks (178 mg, 83%). ES-MS (m/z): [Au6Ag3(C2Ph)7(PPh2C6H4PPh2)3]2+ 1776 (calcd 1776). 31P{1H} NMR (acetone-d6; δ): AB system 1 (P1, P2): 45.08 and 44.22 ppm, J(P-P) 305.3 Hz; AB system 2 (P5, P6): 44.25 and 44.01 ppm, J(P-P) 303.6 Hz; P4 39.82 ppm, unresolved m; P3 10.85 ppm, m, J(107Ag-P 546.7 Hz, 109Ag-P 631.4 Hz), -144.8 (sept, 2P, PF6). 1H NMR (acetone-d6; δ): 8.15-7.25, 72H, a set of complex multiplets corresponding to Ph and C6H4 rings of the diphosphine, 7.30-6.50, 35H, a set of multiplets corresponding to {Ph-C2-Au-} fragments. Anal. Calcd for C146H107Ag3Au6F12P8: C, 45.63; H, 2.81. Found: C, 45.67; H, 2.90. [{Au6Ag6(C2Ph)12}Au3(PPh2(C6H4)2PPh2)3][PF6]3 (2). (PhC2Au)2(PPh2(C6H4)2PPh2) (94 mg, 0.084 mmol) was partially dissolved in THF (10 cm3) under a nitrogen atmosphere. Solid (AuC2Ph)n (25 mg, 0.084 mmol) and (AgC2Ph)n (18 mg, 0.086 mmol) were added followed by a solution of AgPF6 (21 mg, 0.083 mmol) in THF (4 cm3). The reaction mixture was stirred under nitrogen in the absence of light for 2 h to give a transparent yellowish-green solution. It was evaporated to dryness, and the solid residue was recrystallized twice by gas-phase diffusion of pentane into the acetone solution at +5 °C to give yellow-green long blocks (142 mg, 90%). ES-MS (m/z): [Au9Ag6(C2Ph)12(PPh2(C6H4)2PPh2)3]3+ 1733.7 (calcd 1733.67). 31P{1H} NMR (acetoned6; δ): 43.5 (s, 6P), -144.8 (sept, 3P, PF6). 1H NMR (acetone-d6; δ): diphosphine: 8.03 (d, meta-H, (-C6H4-P), 12H, J(H-H) 8.2 Hz), 7.79 (dm (ABXX′), ortho-H, (Ph-P), 24H, J(H-H) 8.4, J(P-H) 13.2 Hz), 7.59 (dm (ABXX′), ortho-H, (-C6H4-P), 12H, J(H-H) 8.2, J(P-H) 12.2 Hz), 7.55 (t, para-H, (Ph-P), 12H, J(H-H) 7.5 Hz), 7.30 (dd, meta-H, (Ph-P), 24H, J(H-H) 8.4, 7.5 Hz); {Au(C2Ph)2} rods (two set of rods A(inner):B(outer) ) 1:1; A: 7.19 (t, para-H, 2H, J(P-H) 7.6 Hz), 6.88 (dd, meta-H, 4H, J(P-H) 7.6, 7.9 Hz), 6.54(d, ortho-H, 4H, J(P-H) 7.9 Hz); B: 6.97 (t, paraH, 6H, J(P-H) 7.6 Hz), 6.62 (d, ortho-H, 12H, J(P-H) 7.7 Hz), 6.28 (dd, meta-H, 12H, J(P-H) 7.6, 7.7 Hz). 13C NMR (acetoned6; δ): diphosphine: 141.45 (s, para-C6H4-P); 135.52 (AXX′, J(P-P) ) 15.9 Hz, ortho-Ph); 135.13 (AXX′, J(P-C) 11.9 Hz, ortho-C6H4-P); 133.32 (s, para-Ph); 131.56 (d, J(P-C) 60.0 Hz, (9) Coates, G. E.; Parkin, C. J. Chem. Soc. 1962, 3220–3226. (10) Teo, B. K.; Xu, Y. H.; Zhong, B. Y.; He, Y. K.; Chen, H. Y.; Qian, W.; Deng, Y. J.; Zou, Y. H. Inorg. Chem. 2001, 40, 6794–6801.

KosheVoy et al. ipso-C6H4-P); 130.23 (AXX′, J(P-C) 11.9 Hz, meta-Ph); 128.13 (AXX′, J(P-C) 10.9 Hz, meta-C6H4-P); 127.95 (d, J(P-C) 56.5 Hz, ipso-Ph); {Au(C2Ph)2} rods (two set of rods A(inner):B(outer) ) 1:1; 133.21 (s, ortho-Ph(A)); 132.87 (s, ortho-Ph(B); 130.43 (s, para-Ph(A)); 129.42 (s, para-Ph(B)); 128.89 (s, meta-Ph(A)); 128.86 (s, meta-Ph(B)); 122.23 (d, J(Ag-C) 1.6 Hz, Au-CtC(A)); 118.78 (s, ipso-Ph(A)); 115.03 (s, ipso-Ph(B)); 114.82 (d, J(Ag-C) 2.5 Hz, Au-CtC(B)); 103.79 (d, J(Ag-C) ) 41 Hz Au-CtC(B)); 92.93 (t, J(Ag-C) 20 Hz Au-CaC(A). Note that J(Ag-C) are the average values of couplings to 107Ag and 109Ag. Anal. Calcd for C204H144Ag6Au9F18P9: C, 43.47; H, 2.58. Found: C, 43.38; H, 2.67. [{Au10Ag12(C2Ph)20}Au3(PPh2(C6H4)3PPh2)3][PF6]5 (3). (PhC2Au)2(PPh2(C6H4)3PPh2) (50 mg, 0.042 mmol) was dissolved in CH2Cl2 (10 cm3), and a solution of AgPF6 (18 mg, 0.071 mmol) in acetone (4 cm3) was added to give a yellow solution. Then solid (AuC2Ph)n (29 mg, 0.097 mmol) and (AgC2Ph)n (20 mg, 0.096 mmol) were added, and the resulting suspension was stirred for 2 h in the absence of light. After filtration the yellow-orange solution was evaporated to dryness and recrystallized twice by gas-phase diffusion of pentane into the acetone solution of the crude product to give fine yellow needles (72 mg, 61%). 31P{1H} NMR (acetoned6; δ): 43.3 (s, 6P), -144.8 (sept, 5P, PF6). 1H NMR (acetone-d6; δ): diphosphine: 8.40 (s, -C6H4-, 12H), 8.36 (d, meta-H, (-C6H4P), 12H, J(H-H) 8.4 Hz), 7.95 (dm (ABXX′), ortho-H, (Ph-P), 24H, J(H-H) 6.8, J(P-H) 13 Hz), 7.70 (dm (ABXX′), ortho-H, (-C6H4-P), 12H, J(H-H) 8.4, J(P-H) 14 Hz), 7.66 (t, para-H, (PhP), 12H, J(H-H) 7.6 Hz), 7.40 (dd, meta-H, (Ph-P), 24H, J(H-H) 8.4, 7.6 Hz); {Au(C2Ph)2} rods (three set of rods A:B:C ) 1:3:6, for numbering scheme see text); A: 7.04 (t, para-H, 2H, J(P-H) 7.6 Hz), 6.84 (d, ortho-H, 4H, J(H-H) 7.0 Hz), 5.85 (dd, meta-H, 4H, J(H-H) 7.0, 7.6 Hz); B: 7.28 (t, para-H, 6H, J(H-H) 7.6 Hz), 6.98 (dd, meta-H, 12H, J(H-H) 7.6, 8.0 Hz), 6.48 (d, ortho-H, 12H, J(H-H) 8.0 Hz); C: 7.15 (t, para-H, 12H, J(H-H) 7.6 Hz), 6.90 (d, ortho-H, 24H, J(H-H) 8.0 Hz), 6.56 (dd, meta-H, 24H, J(H-H) 7.6, 8.0 Hz). Anal. Calcd for C286H196Ag12Au13F30P11: C, 40.90; H, 2.35. Found: C, 40.80; H, 2.37. Photophysical Measurements. An LPX 100 excimer laser (Lambda Physik) and LED (maximum emission at 385 nm) were used to pump luminescence. The laser pulse width is 35 ns, pulse energy is 160 mJ, and repetition rate is 1-25 Hz. LED was used in continuous and pulse mode (pulse width 1-20 µs, duty of edge ∼90 ns, repetition rate 100 Hz to 10 kHz). A Tektronix TDS3014B digital oscilloscope (bandwidth 100 MHz), Hamamatsu photomultiplier tube, and MUM monochromator (LOMO, interval of wavelengths 10 nm) were used for lifetime measurements. Emission spectra were recorded using a HR2000 spectrometer (Ocean Optics). An LS-1-CAL halogen lamp (Ocean Optics) and DH2000 deuterium lamp (Ocean Optics) were used to calibrate the absolute spectral response of the spectral system in the 200-1100 nm range. All solutions were carefully degassed before lifetime measurements. Lifetime measurements were done using laser (308 nm) and LED (maximum emission at 385 nm) pumping; mono- and diexponential decays were observed in the microsecond domain. The absolute emission quantum yield was determined by Vavilov’s method11 using LED (385 nm, continue mode) pumping and Cumarin 307 (Φem ) 0.95 ( 0.2) as a standard. Computational Details. The studied supramolecular Au(I)-Ag(I) complexes were fully optimized without any symmetry constraints using the BP86 density functional method.12 Standard GGA density functionals such as BP86 cannot accurately describe the energetics of weak dispersive metal-metal interactions between closed-shell metal atoms. However, the structural chemistry of the supramolecular complexes studied here is dominated by the electrostatic (11) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991–1024. (12) (a) Becke, A. D. Phys. ReV. A 1988, 3098–3100. (b) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys 1980, 58, 1200–1211. (c) Perdew, J. P. Phys. ReV. B 1986, 33, 8822–8824.

Gold(I)-SilVer(I) Alkynyl-Phosphine Complexes

Organometallics, Vol. 28, No. 5, 2009 1371

interactions between the Ag(I) ions, the [PhC2AuC2Ph] rods, and the gold-diphosphine “belt”.2,13 The silver and gold atoms were both described with a triple-valence-zeta quality basis set with polarization functions (def2-TZVP),14 employing 28-electron and 60-electron relativistic effective core potentials for Ag and Au, respectively.15 A split-valence basis set with polarization functions on non-hydrogen atoms was used for all other atoms (def2-SV(P)).16 The multipole-accelerated resolution-of-the-identity technique was used to speed up the calculations.17 All electronic structure calculations were carried out with TURBOMOLE version 5.10.18

Results and Discussion Synthesis and Characterization. The reaction of the digold complex [Au2(CtCPh)2(µ-1,4-PPh2C6H4PPh2)] with AgPF6 in THF leads to the formation of a complicated mixture of products, from which the novel cluster compound [{Au3Ag2(C2Ph)6}Au3Ag(C2Ph)(PPh2C6H4PPh2)3][PF6]2 (1) was isolated after repetitious recrystallization. Optimization of the reaction conditions (Scheme 1) allowed for the selective preparation of 1 in moderately good yield. Bright yellowish-green, air-stable, but slightly moisturesensitive complex 1 has been studied by 31P NMR and ESI-MS spectrometry. The ESI mass spectrum of 1 (Figure S1, S denotes Supporting Information) displays a signal of a doubly charged cation at m/z 1776, the isotopic pattern of which completely fits the stoichiometry of the [{Au3Ag2(C2Ph)6}Au3Ag(C2Ph)(PPh2C6H4PPh2)3]2+ molecular ion. Due to the low symmetry of 1 (Figure 1), its 1H and 13C spectra are very complicated and poorly resolved, as all the signals correspond to the aromatic C6H4 and C6H5 groups and appeared in a rather narrow spectral region. Nevertheless, the data of 31P NMR spectroscopy together with crystallographic information made it possible to reveal the essential structural features of the molecule. The solid-state structure of 1 has been determined by X-ray crystallographic analysis. However, poor diffraction of the crystals did not allow for high-quality refinement (see Supporting Information for the structure determination details and an ORTEP view of the dication 1, Figure S2). Scheme 1

The molecule contains the central [Au3Ag2(C2Ph)6] fragment, which is wrapped by an open-loop tetrametallic diphosphinealkynyl [Au(C2Ph)Au2Ag(PPh2C6H4PPh2)3]3+ “belt” anchored to the central part by two Au-Au and one Au-Ag bond. The central fragment consists of three slightly twisted [PhC2AuC2Ph] rods held together by Ag-Au and π-CtC-Ag bonding. Interestingly, in the case of a closely analogous Au-Cu “rodsin-belt” aggregate we observed formation of the highly symmetrical molecule [{Au3Cu2(C2Ph)6}Au3(PPh2C6H4PPh2)3][PF6]22, where idealized D3hsymmetry is retained for both the pentanuclear Au3Cu2 cluster and closed [AuPPh2C6H4PPh2]33+ “belt”. A probable reason for this “incomplete wrapping” in 1 is a significantly larger size of the {Au3Ag2(C2Ph)6} fragment compared to its copper analogue. The Au · · · Au distances within this fragment in 1 exceed 3.9 Å (average 4.0 Å, see Supporting

Figure 1. Schematic structure of dication 1. Phenyl rings are omitted for clarity.

Figure 2. 31P NMR spectrum of 1 (121.5 MHz, acetone-d6, 298 K, * denote admixtures).

Information), which is slightly longer than those determined in the unwrapped anion.13,19 On the contrary, the average Au · · · Au contact in the copper analogue [{Au3Cu2(C2Ph)6}Au3(PPh2C6H4PPh2)3][PF6]2 is ca. 3.34 Å, which is shorter than the value found in the free [Au3Cu2(C2Ph)6]- anion (av 3.472 Å).20 It seems therefore that “complete wrapping” of the gold-silver cluster would result in too short and unfavorable Au-Au contacts between the large central {Au3Ag2(C2Ph)6} fragment and the wrapping “belt” (see also computational results below). It is worth mentioning that metallophilic interactions enhanced by Coulomb forces between the cationic complex [(Me3P)2Ag]+ and [Ag2Au3(C2Ph)6]- anion have been observed.13 The NMR data obtained for the complex 1 are completely consistent with the structure described above. The 1D 1H and 1 H-1H COSY spectra of 1 show the presence of two sets of multiplets corresponding to the phenyl rings of the {Ph-C2-Au-} fragments (7.30-6.50, 35H) and to the Ph and C6H4 moieties (8.15-7.25, 72H) of the diphosphine ligands. The 31P NMR spectrum of 1 (Figure 2) is much more informative relative to the design of the polymetallic framework of this complex. The high-field multiplet centered at 10.85 ppm clearly displays resolved one-bond coupling to 107Ag and 109Ag (546.7 (13) Schuster, O.; Monkowius, U.; Schmidbaur, H.; Ray, R. S.; Kruger, S.; Rosch, N. Organometallics 2006, 25, 1004–1011. (14) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297– 3305. (15) Andrae, D.; Ha¨ussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chem. Acc. 1990, 77, 123–141. (16) Scha¨fer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571– 2577. ¨ hm, H.; Ha¨ser, M.; Ahlrichs, R. (17) (a) Eichkorn, K.; Treutler, O.; O Chem. Phys. Lett. 1995, 240, 283–290. (b) Sierka, M.; Hogekamp, A.; Ahlrichs, R. J. Chem. Phys. 2003, 118, 9136–9148. (c) Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R. Theor. Chem. Acc. 1997, 97, 119– 124. (d) Weigend, F. Phys. Chem. Chem. Phys. 2006, 8, 1057–1065. (18) Ahlrichs, R.; Ba¨r, M.; Ha¨ser, M.; Horn, H.; Ko¨lmel, C. Chem. Phys. Lett. 1989, 62, 165–169. (19) (a) Ul-Haque, M.; Horne, W.; Abu-Salah, O. M. J. Crystallogr. Spectrosc. Res. 1992, 22, 421–425. (b) Hussain, M. S.; UI-Haque, M.; AbuSalah, O. M. J. Cluster Sci. 1996, 7, 167–177. (20) Abu-Salah, O. M.; Al-Ohaly, A. R. A.; Knobler, C. B. J. Chem. Soc., Chem. Commun. 1985, 1502–1503.

1372 Organometallics, Vol. 28, No. 5, 2009 Scheme 2

and 631.4 Hz, respectively), which allows assignment of the signal to the P(3) atom bonded to Ag(3). The signal of P(4) appears at 39.82 ppm as an unresolved multiplet due to the longrange coupling to P(3) and 107Ag and 109Ag nuclei. The pairs of slightly inequivalent P(1)-Au(2)-P(2) and P(5)-Au(6)-P(6) phosphorus nuclei generate two AB systems, which display strong two-bond phosphorus-phosphorus coupling, 305.3 and 303.6 Hz, respectively. The assignment given above is strongly supported by the 31P-31P COSY spectrum shown in Figure S3. These observations indicate that the structure found in the solid state remains unchanged in solution. The reaction of the gold complex [Au2(CtCPh)2(µ-4,4′PPh2(C6H4)2PPh2)], based on a diphosphine with a biphenyl spacer between phosphorus atoms, with stoichiometric amounts of AgPF6, [AuCtCPh]n, and [AgCtCPh]n leads to clean formation of the bright yellowish-green, light-sensitive complex [{Au6Ag6(C2Ph)12}Au3(PPh2(C6H4)2PPh2)3][PF6]3 (2) (Scheme 2). The composition and structure of this cluster were established on the basis of the 1H, 13C, and 31P NMR and ESI-MS measurements. This complex evidently adopts the same structural topology as its Cu relative6 and consists of the dodecanuclear [Au6Ag6(C2Ph)12] cluster incorporated into the [Au(PPh2(C6H4)2PPh2)]33+ triangle (Figure 3). The ESI mass spectrum of 2 (Figure S4) displays a pattern of a triply charged molecular cation at m/z 1733.7 that completely fits the stoichiometry given above. Attempts to prepare the central part of 2 as an individual complex [Au6Ag6(C2Ph)12] similar to its copper analogue [Au6Cu6(C2Ph)12]6 were unsuccessful in giving eventually a light-sensitive insoluble material. The NMR data obtained for 2 fit completely the structure proposed. The 31P spectrum of 2 displays one singlet resonance centered at 43.5 ppm that is indicative of the presence of a thirdorder symmetry axis in the molecule as shown above. The 1 H-1H COSY spectrum of 2 (Figure S5) allows for unambiguous assignment of the signals in the 1D proton spectrum given in the Experimental Section. The low-field group of signals

Figure 3. Schematic structure of trication 2. Phenyl rings are omitted for clarity.

KosheVoy et al.

between 8.1 and 7.25 ppm can be easily assigned to the phenyl rings and phenylene spacers of the diphosphine ligands on the basis of COSY correlations and their couplings to the phosphorus nuclei. The high-field set of resonances (7.19-6.28 ppm) is split into two groups of phenyl protons, each of which corresponds to three [PhC2AuC2Ph] rods. The rods are different in their disposition relative to the gold atoms of the [Au(PPh2(C6H4)2PPh2)]3 “belt” to form inner (A) and outer (B) triangles, as shown in Figure 3. A similar separation of the signals into three groups mentioned above is also observed in the 13C spectrum of 2 together with specific couplings to phosphorus and silver nuclei. The latter is indicative of the triple bonds coordination to silver ions and also points to asymmetry of this interaction because 1J(Ag-C) are very different for the alkyne carbons, e.g., 1.6 vs 20 Hz and 2.5 vs 41 Hz for inner and outer “rods”. These spectroscopic data are completely compatible with the D3h symmetry of the molecule shown in Figure 3. The use of the terphenyl-based gold complex [Au2(CtCPh)2(µ4,4′′-PPh2(C6H4)3PPh2)] as a starting material in the reaction similar to the preparations of 1 and 2 (Scheme 3) allowed for the synthesis of the yellow cluster [{Au10Ag12(C2Ph)20}Au3(PPh2(C6H4)3PPh2)3][PF6]5 (3). Complex 3 did not give crystals suitable for X-ray analysis, and its composition and structure have been established on the basis of its elemental analysis and detailed investigation of the 1 H and 31P NMR spectroscopic characteristics together with comparison of the data obtained for its copper congener, [{Au10Cu12(C2Ph)20}Au3(PPh2(C6H4)3PPh2)3][PF6]5.2 Similarity of the chemistry observed in the reactions of the [Au2(CtCPh)2(µPPh2(C6H4)nPPh2)] (n ) 2, 3) complexes with Ag+ and Cu+ ions suggests that these self-assembly processes, which yield multinuclear heterometallic aggregates, have a rather general character and, very probably, reaction mechanism. This resemblance also allows assuming that structural patterns of the final products are based on the same stereochemical motif. Thus, the molecular architecture of 3 may be presented in the way shown in Figure 4. Like in the copper analogue, three gold atoms in 3 join together three molecules of the diphosphine ligands to give a Scheme 3

Figure 4. Schematic structure of pentacation 3. Phenyl rings are omitted for clarity.

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Figure 5. 1H-1H COSY spectrum of 3 (300 MHz, acetone-d6, 298 K) (A) and schematic numbering scheme (B).

triangular “belt”, which wraps around the central fragment [Au10Ag12(C2Ph)20]; see Scheme 3 and Figure 4. Expansion of the diphosphine ligand’s length compared to 2 results in an increase of the internal space inside the “belt” and requires subsequent growth of the central fragment. The same structural trend was observed for the series of analogous Au(I)-Cu(I) aggregates.2 The NMR spectroscopic data for 3 and their comparison with those of the Cu relative strongly support this structural hypothesis. The presence of one singlet in the 31P NMR spectrum of 3 is completely compatible with the structure shown in Figure 4, where all phosphorus atoms are equivalent in the D3h symmetry group. The 1H NMR spectroscopic data (Figure 5) also fit well the composition and symmetry of the molecular pattern. Very similar to the copper relative2 and lower-nuclear congener 2, the proton resonances of the diphosphine ligands and alkynyl rods are well separated in the spectrum, the relative intensity of the corresponding signals being in excellent agreement with the stoichiometry suggested for 3. The lowfield part of the spectrum (8.5-7.35 ppm) displays a set of multiplets related to each other by the cross-peaks in the COSY spectrum and showing characteristic coupling patterns for the protons adjacent to the phosphorus nuclei. In particular, the ortho-protons of the phenyl rings and phenylene spacers display ABXX′ multiplets (X,X′ are magnetically inequivalent phosphorus nuclei bound to the same Au center with 2J(P-P′) . 3 J(P-H)), which is a clear indication of the closed triangular structure of the [Au(diphosphine)]3 “belt”, where phosphorus nuclei of the diphosphine ligands are strongly coupled through the gold center. In turn, the high-field part of the spectrum (7.35-5.75 ppm) contains three sets of phenyl ring signals (ortho(d)-meta(dd)-para(t)) with relative intensities of 1/3/6. This fits completely the structure of the central heterometalic cluster shown in Figures 4 and 5. In accord with D3h symmetry of the molecule, ten [PhC2AuC2Ph] rods form an outer triangular shell made of nine dialkynyl fragments adjacent to the diphosphine belt (B and C phenylacetylene ligands in Figure 5B). This shell consists of three equivalent dialkynyl rods in the corners of the triangle (B phenylacetylene ligands) together with six rods disposed on the sides of the triangle (C phenylacetylene ligands). In turn this shell wraps around the unique central Au-dialkynyl unit, which fits completely the relative intensities of the proton signals mentioned above. The agreement between the suggested highly symmetrical structure of 3 and its NMR spectroscopic data together with their similarity to those of the previously characterized gold-copper complex2 leaves nearly no room for alternative structural models.

Photophysical Characteristics of Supramolecular Au-Ag Aggregates. Not surprisingly, like many other polynuclear gold-silver complexes5,8,21 and gold-copper analogues,2 the series of gold-silver complexes discussed in the present paper are intensely luminescent. The UV-vis spectra of 1-3 consist of a strong absorption in the near-UV region, which includes one or two overlapping bands (260-320 nm) together with a featureless high-energy absorption, and clear-cut low-energy bands at 364, 388, and 390 nm, respectively. All the components of these spectra are progressively red-shifted with the increase in the size of the dialkynyl cluster nuclei. Computational analysis of the electronic structure of these complexes and comparison with the data obtained earlier for Au-Cu relatives allow for the assignment of the high-energy2,6 absorption to intraligand transitions, whereas near-UV bands are very likely generated by the electronic transitions from the orbitals localized at the central cluster fragment to antibonding orbitals of alkynyl and/ or phosphine ligands. In turn, the low-energy absorption bands observed in the visible area of these spectra are associated with the transitions between the orbitals of the cluster core. It is also worth noting that the visible absorption bands in 1-3 are blueshifted (20-40 nm) compared to their gold-copper analogues, which points to an increase in the energy gap between the orbitals responsible for these transitions. A similar effect for substitution of Cu(I) for Ag(I) ions was observed in the electronic spectra of the [Au3M2(CtCR)]- complexes (M ) Cu, Ag),22 where the corresponding absorption bands of silver relatives are blue-shifted by only ca. 10 nm. The presence of the trigold-phosphine belt in 1-3 substantially increases this blue shift, which indicates an increase in the energy gap between the corresponding orbitals.

Figure 6. Normalized emission spectra of complexes 1-3 in dichloromethane at ambient temperature, λexc 385 nm.

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Table 1. Spectroscopic Characteristics of 1-3, CH2Cl2, 298 K, λexc ) 385 nm compound 1 2b 3b 3b,c

λabs/nm, (10-3/dm3 mol-1 cm-1)

λem/nm; τ/µs

Φem

507; 0.52 ( 0.01 0.29 ( 0.02 ca. 560; 2.9 ( 0.5a 270 (205); 284 (208); 388(69) 512; 1.23 ( 0.05 0.35 ( 0.05 559; 4.6 ( 0.1a 261 (259); 319 (247); 390 (67) 571; 4.9 ( 0.2 0.023 ( 0.002 568; 4.5 ( 0.1 259 (170); 364 (52)

a Second component of emission with less than 5% contribution to total decay intensity. b Complexes 2 and 3 are photochemically unstable, decomposing under steady-state irradiation; therefore the emission characteristics given in the table are restricted to initial stage of irradiation of a freshly prepared solution. c Solution in acetone.

Luminescence spectra of 1-3 are shown in Figure 6. The compounds under study exhibit a systematic red shift in the λemmax with the growth of the central core from 507 nm for 1 to 512 and 571 nm for 2 and 3, respectively. This reduction in emission energy is in agreement with computational results (Vide infra) predicting a decrease in the HOMO-LUMO gap on going from 1 to 3. Emissive excited states of 1-3 display singleexponential decay with a very small contribution of a slightly red-shifted emission in 1 and 2. At least in the case of 2 this minor component is due to the presence of a decomposition product, which is the only luminescent compound left in solution after prolonged irradiation of the mixture. The lifetime of the main components of luminescence is in the microsecond domain, which points to the triplet origin of the excited states for all three complexes. The phosphorescence lifetime values show a systematic increase in the order 1 (0.52 µs), 2 (1.23 µs), and 3 (4.9 µs). Generation of the emission using shorter wavelength (308 nm, eximer laser) irradiation does not change the luminescence characteristics, which is indicative of effective intersystem crossing in all compounds under study. In line with the blue shift of absorption spectra of 1-3 compared to the structurally related gold-copper complexes,2 emission of gold-silver analogues is also blue-shifted by ca. 80-90 nm. Luminescence properties of the “core” Au3Ag2 alkynyl complexes were studied earlier.22 The monoanionic complexes [Au3Ag2(C2C6H4-R)6]- display phosphorescence at 457, 488 nm (3.7 µs) (R ) Et) and 471 nm (4.2 µs) (R ) OnHex), which is considerably blue-shifted relative to phosphorescence of 1 (507 nm (0.52 µs)), containing the same pentanuclear alkynyl cluster as the central core. The effect of the triphosphine belt in this case consists in the red shift of the phosphorescence and substantial decrease in emission lifetime compared to the “unfastened” pentanuclear core. Emission quantum yields of 1and 2 are very similar, 0.29 and 0.35, respectively, and considerably higher compared to that of 3 (0.023), which is probably a consequence of effective quenching of the phosphorescence associated with the bigger central cluster core. Computational Results. The structural and electronic properties of the supramolecular Au(I)-Ag(I) complexes were elucidated by density functional calculations (for the computational details, see the Experimental Section). The optimized geometries and selected structural parameters of all three studied “rods-in-belt” complexes are shown in Figure 7. In the case of the smallest complex 1, comparison between the optimized geometry and the crystal structure shows the theoretical and (21) (a) Wang, Q.-M.; Lee, Y.-A.; Crespo, O.; Deaton, J.; Tang, C.; Gysling, H. J.; Gimeno, M. C.; Larraz, C.; Villacampa, M. D.; Laguna, A.; Eisenberg, R. J. Am. Chem. Soc. 2004, 126, 9488–9489. (b) Catalano, V. J.; Horner, S. J. Inorg. Chem. 2003, 42, 8430–8438. (22) Yip, S.-K.; Chan, C.-L.; Lam, W. H.; Cheung, K.-K.; Yam, V. W.W. Photochem. Photobiol. Sci. 2007, 6, 365–371.

Figure 7. Optimized geometries and selected structural parameters for the dication 1 (top left), trication 2 (top right), and pentacation 3 (bottom). For 1, the experimental metal-metal structural parameters (see Supporting Information) are listed in parentheses. The complexes are shown from a top view, omitting phenyl rings and hydrogen atoms for clarity.

experimental metal-metal structural parameters to be in good agreement. The structural characteristics of the larger complexes 2 and 3 are closely similar to each other, suggesting that the central fragment fits reasonably well inside the “belt” fragment. In both complexes, all the supramolecular Au-Au bond contacts between the central and “belt” fragment remain at 2.88 Å. In the case of the previously studied triangular Au(I)-Cu(I) complexes analogous to 2 and 3,2 the match between the diameters of the central and the “belt” fragments is worse due to the smaller size of the Cu(I) ion in comparison to Ag(I). For example, in the pentacationic Au(I)-Cu(I) complex [{Au10Cu12(C2Ph)20}Au3(PPh2(C6H4)3PPh2)3][PF6]5, the supramolecular Au-Au bond contacts vary between 3.11 and 3.91 Å. In addition to the three experimentally characterized “rodsin-belt” complexes, we optimized the structure of a hypothetical, symmetric modification of 1, [{Au3Ag2(C2Ph)6}Au3(PPh2C6H4PPh2)3]2+ (1a), where the “belt” fragment is geometrically similar to those in the larger complexes 2 and 3 and forms a closed cycle. In this symmetric cluster 1a, the supramolecular Au-Au bond contacts, Au-Ag contacts, and the Au-Au distances within the central fragment were found to be 2.84, 2.95, and 3.75 Å, respectively. For comparison, the corresponding structural parameters in 1 are 2.98, 2.95-3.00, and 3.92-4.08 Å. Hence, a symmetric modification of 1 would possess significantly shorter metal-metal distances in comparison to the experimentally observed structure. Considering that the larger symmetric complexes 2 and 3 also adopt structures where the metal-metal distances within the central fragment are much longer than those found for the symmetric modification 1a, it seems that the central fragment of 1 is too large to fit inside a corresponding symmetric “belt” fragment. Therefore, the supramolecular assembly of a D3h-symmetric Au(I)-Ag(I) complex with a Au3Ag2 core is likely to be hindered by steric reasons, resulting in a distorted “belt” fragment. In addition to the structural characteristics of the supramolecular Au(I)-Ag(I) complexes, we investigated their electronic

Gold(I)-SilVer(I) Alkynyl-Phosphine Complexes

Figure 8. Frontier molecular orbital isodensity plots for the S0 and T1 states of the dicationic Au(I)-Ag(I) complex 1 (isodensity value 0.04). Phenyl rings of the “belt” fragment and hydrogen atoms are omitted for clarity. SOMO ) singly occupied molecular orbital.

properties to obtain insights into their photophysical behavior. The frontier orbital characteristics of the S0 and T1 electronic states of the dication 1 are illustrated in Figure 8. The HOMO and HOMO-1 of the dication 1 are both centered on the central fragment, being composed of ligand π(CtCPh), d(Au), and d(Ag) orbitals. The LUMO is composed of the central fragment sp(Ag), sp(Au), and ligand π*(CtCPh) orbitals, while LUMO+1 is delocalized over the bridging Ph groups of the “belt” fragment. Structural optimization of the lowest-lying triplet state resulted in a decrease of the Ag-Ag distance (from 3.77 to 3.48 Å), the structural changes in general being quite small, however. As can be expected from the overall similarity of the S0 and T1 geometries, the lowest singly occupied MO of the T1 state is related to the S0 HOMOs, and the highest singly occupied MO is related to the S0 LUMO, possessing a significant metal sp character (Figure 8). In comparison to the structurally related supramolecular Au(I)-Cu(I) complex with a Au3Cu2 metal core, the contribu-

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tion of the ligand orbitals to the HOMOs is much larger in the dication 1, with a Au3Ag2 central cluster.2 The d(Ag) and sp(Ag) orbitals are shifted down in energy in comparison to the corresponding Cu(I) orbitals, Ag(I) ions being less prone to further oxidation than Cu(I) ions. Consequently, in the case of the supramolecular Au(I)-Ag(I) complexes, the HOMOs possess less d(Ag) character and the LUMO possesses more sp(Ag) character than in the case of the related copper species. The HOMO-LUMO gap increases from 1.80 to 2.01 eV when moving from Cu(I) to Ag(I) species, in accordance with the experimentally observed blue shift of the lowest energy absorption and emission bands when moving from Cu(I) to Ag(I). The determined frontier orbital characteristics and different electronic properties of the Cu(I) and Ag(I) species are in good agreement with the results obtained by Yip et al. for the closely related [Au3M2(CtCC6H4Me-p)6]- complexes (M ) Cu, Ag).22 In addition, previous theoretical studies of the Au3Ag2(C2Ph)6central fragment of the dication 1 have shown the interactions within Au3Ag2(C2Ph)6- species to be mainly electrostatic.13 Considering the electronic characteristics of the dication 1, the experimentally observed near-UV and low-energy absorption bands are likely to be associated with alkynyl ligand and central metal core related transitions such as metal-perturbed intraligand [π f π*(CtCPh)], MLCT [d(Au,Ag) f π*(CtCPh)], and metal-centered transitions. The initial excited states then end up at the emitting triplet state via intersystem crossing. The nature of the lowest-lying triplet state suggests the observed long-wavelength triplet emission to originate from transition from metal sp orbitals down to the HOMO composed of alkynyl ligand π orbitals and metal d orbitals. The frontier orbitals of the larger complexes 2 and 3 resemble those of 1. The HOMOs composed of ligand π(CtCPh), d(Ag), and d(Au) orbitals are mainly centered on the “corners” of the central fragment connected to the “belt” fragment. In contrast to the HOMOs, the LUMOs composed of central fragment sp(Ag), sp(Au), and ligand π*(CtCPh) orbitals are mainly centered on the middle of the central fragment. As the size of the heterometallic core increases, the HOMO-LUMO gap decreases, possibly due to the LUMOs being shifted down due to the growing number of nonbonding metal sp orbitals mixed into them. The HOMO-LUMO gaps of 1, 2, and 3 are 2.01, 1.95, and 1.37 eV, in agreement with the experimentally observed red shift of the emission maximum with increasing core cluster size. Overall, the theoretical results obtained for the supramolecular Au(I)-Ag(I) complexes support the proposed “rods-in-belt” structural motif. The experimentally observed structural and photophysical differences in comparison to the related Au(I)-Cu(I) species could also be elucidated with a detailed investigation of geometrical and electronic properties of the complexes. The luminescence features of the Au(I)-Ag(I) complexes can be associated with transitions within the central Au(I)-Ag(I) heterometallic fragment.

Conclusion The results presented here show an extension of our recent studies of the Au(I)-Cu(I) alkynyl-diphosphine supramolecular systems2,6 aimed at modification of the composition of the metal framework. Thus, Ag+-promoted self-assembly of the simple alkynyl-diphosphine complexes of Au(I) affords novel “rodsin-belt” aggregates, in which the [PhC2AuC2Ph]- “rods” are held together by Ag-Au and π-CtC-Ag bonding to form central heterometallic clusters, which are “wrapped” around by the golddiphosphine “belts”, anchored to the central part by Au-Au

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bonds. The central fragments [AuxAgy(C2Ph)2x]y-x (x ) (n+1)(n+2)/2; y ) n(n+1); n ) 1, 2, 3) of these species display very similar structural patterns to the Au(I)-Cu(I) clusters, where the gold atoms lie in one plane while the silver ones occupy positions above and below this plane. However, the composition of the external “belt” depends on the size of the “wrapped” fragment: in the case of n ) 2, 3 it is a symmetrical closed triangle [Au3{PPh2(C6H4)nPPh2}3]3+, but when n ) 1 the “belt” is the open-loop tetrametallic diphosphine-alkynyl [Au(C2Ph)Au2Ag(PPh2(C6H4)2PPh2)3]3+ complex. These complexes demonstrate efficient room-temperature luminescence in solution with a maximum quantum yield of 0.35. However, the photostability and photoefficiency of these Au(I)-Ag(I) aggregates are substantially lower that those of the Au(I)-Cu(I) congeners. Theoretical results obtained are in good agreement with the experimental data, supporting the proposed structural motif. These studies also suggest that the observed luminescence is

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associated with transitions within the central Au(I)-Ag(I)alkynyl fragment. The reported studies prove a universal character of the self-assembling process that opens wide possibilities for functionalization of these luminophores and possible tuning of the photophysical characteristics.

Acknowledgment. Financial support from the Academy of Finland (I.O.K.) and Russian Foundation for Basic Research (grant 07-03-00908-a) is gratefully acknowledged. Supporting Information Available: X-ray crystallographic data in CIF format and X-ray crystal structure determinations for 1; 1 P-1P COSY spectrum of 1; 1H-1H COSY spectrum of 2; ESImass spectra of 1, 2; optimized Cartesian coordinates of the studied systems in atomic units. This material is available free of charge via the Internet at http://pubs.acs.org. OM8010036