Luminescent Gold(I) Alkynyl Clusters Stabilized by Flexible

Apr 30, 2014 - ... complexes are linked to the gold–diphosphine units [Au2(diphosphine)]2+ by Au–Au interactions and π C≡C–Au bonding, thus f...
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Luminescent Gold(I) Alkynyl Clusters Stabilized by Flexible Diphosphine Ligands Igor O. Koshevoy,*,† Yuh-Chia Chang,‡ Yi-An Chen,‡ Antti J. Karttunen,§ Elena V. Grachova,∥ Sergey P. Tunik,*,∥ Janne Jan̈ is,† Tapani A. Pakkanen,† and Pi-Tai Chou*,‡ †

Department Department § Department ∥ Department ‡

of of of of

Chemistry, Chemistry, Chemistry, Chemistry,

University of Eastern Finland, Joensuu 80101, Finland National Taiwan University, Taipei 106, Taiwan Aalto University, FI-00076 Aalto, Finland St. Petersburg State University, Universitetskii pr. 26, 198504 St. Petersburg, Russia

S Supporting Information *

ABSTRACT: Treatment of the homoleptic decanuclear compounds (AuC2R)10 with the cationic gold diphosphine complexes [Au2(PR′2-X-PR′2)2]2+ results in high-yield formation of the new family of hexanuclear clusters [Au6(C2R)4(PR′2-X-PR′2)2]2+ (PR′2-X-PR′2 = PPh2-(CH2)nPPh2, n = 2 (1, R = diphenylmethanolyl), n = 3 (3, R = diphenylmethanolyl; 4, R = 1-cyclohexanolyl; 5, R = 2borneolyl), 4 (6, R = 1-cyclohexanolyl); PR′2-X-PR′2 = PCy2(CH2)2-PCy2 (2, R = diphenylmethanolyl); PR′2-X-PR′2 = 1,2(PPh2-O)-C6H4 (7, R = diphenylmethanolyl); PR′2-X-PR′2 = (R,R)-DIOP (8, R = diphenylmethanolyl)). In the case of PPh2-(CH2)4-PPh2 phosphine and −C2C(OH)Ph2 alkynyl ligands an octanuclear cluster of a different structural type, [Au8(C2C(OH)Ph2)6(PPh2-(CH2)4-PPh2)2]2+ (9), was obtained. Complexes 1− 3, 7, and 9 were studied by X-ray crystallography. NMR and ESI-MS spectroscopic investigations showed that all but two (2 and 9) compounds are fluxional in solution and demonstrate dissociative chemical equilibria between major and a few minor forms. All of these complexes are intensely emissive in the solid state at room temperature and demonstrate very high quantum yields from 0.61 to 1.0 with weak influence of the alkynyl substituents R′ and the diphosphine backbones on luminescence energies. Two crystalline forms of the cluster 2 (P21/n and P21 space groups) exhibit unexpectedly contrasting yellow and sky blue emission, maximized at 572 and 482 nm, respectively. Electronic structure calculations with density functional methods demonstrate that the transitions responsible for the highly effective phosphorescence are dominated by contributions from the Au and π-alkynyl orbitals.

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INTRODUCTION The closed-shell metal−metal interactions, found among the gold(I) ions,1 often lead to diverse self-assembled aggregates of unusual stoichiometries and structures both in the solid state and in solution. Employment of this type of chemical bonding for the synthesis of polymetallic compounds made the supramolecular chemistry of gold a fast-growing research area, which has been extensively developed over the past two decades.2 In addition to the attractive variety of gold(I) frameworks, the aurophilic contacts result in a dramatic change or emergence of intriguing luminescent properties.3 Moreover, the gold-containing materials exhibit impressive stimulidependent variations of photophysical characteristics, such as vapo-,3d,4 mechano-,4b,5 or tribochromic6 luminescence, which mainly depend on modulation of the intermetallic bonds in the solid state. The influence of aurophilic interactions on the absorption and emission properties of gold(I) compounds was also elegantly used for the elaboration of a number of luminescent chemosensing systems in solution.7 Among a wide selection of the element-organic ligands used for the © 2014 American Chemical Society

preparation of gold(I) complexes, the alkynyl moiety has proven to be a superior building block due to the relatively easy synthesis and good stability of the resulting compounds, together with the well-documented ability of the CC unit to bind metal ions in a σ,π-bridging mode that facilitates formation of supramolecular aggregates. Surprisingly, although a large number of gold(I) alkynyl coordination complexes of general formula LAuC2R (L = phosphine, pyridine, isonitrile) have been reported,8 the molecular alkynyl gold clusters remain limited.9 Recently we have shown that employment of hydroxy aliphatic alkynes allows for the isolation of intensely luminescent homoleptic decanuclear clusters (AuC2R)10, which can be effectively converted into octanuclear diphosphine derivatives upon treatment with the cationic complexes [Au2(PPh2-X-PPh2)2]2+ (X = −CC−, −C6H4−).10 The latter compounds adopt two different structural types, determined by Received: March 19, 2014 Published: April 30, 2014 2363

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Compounds 1−8 were characterized by 1H and 31P NMR spectroscopy and ESI-MS. The crystal structures of complexes 1−3 and 7 were determined by X-ray diffraction studies (Figure 2 and Figure S1; the ORTEP views are also shown in Figure S2 (Supporting Information)). The selected interatomic distances are given in Table S2 (Supporting Information). Complex 2 crystallizes in two forms, 2A (P21/n space group) and 2B (P21 space group), which show different photophysical behaviors (see the luminescence characteristics below). The molecules of complexes 1−3 and 7 consist of two dialkynylgold linear anionic fragments, connected by a Au(5)−Au(6) bond and twisted with respect to each other (the torsion angle C(1)− Au(5)−Au(6)−C(3) falls in the range 45.7−49.5° in 1, 2, and 7 and equals 56.3° in 3). The [Au(C2R)2]− rods in these complexes are linked to the gold−diphosphine units [Au2(diphosphine)]2+ by Au−Au interactions and π CC− Au bonding, thus forming the hexanuclear metal framework. This structural motif may be considered as a cluster core composed of two fused Au4 tetrahedra with one common Au(5)−Au(6) edge. The bridging diphosphines span the Au(1)−Au(2) and Au(3)−Au(4) edges of the Au6 polyhedron. However, due to the rather large ligand bite angles the average values of the spanned Au−Au distances exceed 3.22 Å. In the clusters 2 (B form) and 7 the corresponding bonds are lengthened up to 3.4164(5) and 3.3699(5) Å, respectively, which clearly points to a weak aurophilic interaction, as these values are substantially higher than the sum of Au van der Waals radii (3.32 Å). Due to the binding mode of the diphosphines, which are twisted with respect to the Au(1)−Au(2) and Au(3)−Au(4) bonds, the resulting cluster cations exhibit propeller-like chirality (Scheme 1). An increase in the length of the diphosphine ligand for the crystallographically characterized complexes 1−3 and 7 did not reveal any systematic variations in the structural parameters of the cluster frameworks. The distances between O(1)−O(2) and O(3)−O(4) atoms lie in the range 2.74−3.03 Å (with the only exception of O(1)−O(2) in 3 being 3.93 Å), pointing at effective O···H−O hydrogen-bond formation between the hydroxyl groups of the alkynyl ligands. These intramolecular interactions along with aurophilic bonding additionally stabilize the molecular aggregates under study. The ESI-MS of 1−3 show the signals of the doubly charged cations at m/z 1403.2, 1427.4, and 1417.2 (Figure S3, Supporting Information), the isotopic patterns of which match completely the stoichiometry of the [Au6(C2C13H11O)4(diphosphine)2]2+ molecular ions. However, the mass spectra of 4−6 and 8 display dominating signals of the monocations at m/z 1249.2, 1357.3, 1263.2, and 1335.3, which clearly indicate the dissociation of the hexanuclear clusters into the trinuclear fragments [Au3(C2R)2(diphosphine)]+. The VT 31 P NMR spectra of 1−8 (Figures S4−S18, Supporting Information) also display the presence of another phosphinecontaining complex in solution and the position of the corresponding signals testifies that the phosphorus ligands remain coordinated. It is also worth noting that the amount of these species increases upon an increase in temperature. These observations are in agreement with the mass spectroscopic data and point to the presence of a dissociative equilibrium in solution. Complex 6 could not be satisfactorily characterized in solution due to its very poor solubility and instability in common organic solvents. The NMR spectroscopic studies of the complexes 1−8 reveal that at room temperature all but one (2) of the compounds

the stereochemical properties of the phosphine ligands (Figure 1).

Figure 1. Representation of the structural types of octanuclear gold(I) alkynyl clusters depending on the ancillary diphosphine ligands.

Herein we report on the investigation of self-assembly processes of the related gold alkynyl clusters using a family of the flexible PPh2-X-PPh2 diphosphines with variable lengths of the aliphatic spacer X.

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RESULTS AND DISCUSSION Synthesis and Characterization. The reaction of the decanuclear cluster (AuC2R)10 (R = C(OH)Ph2) with the cationic gold diphosphine complex [Au2(dppe)2]2+ (dppe = PPh 2-(CH 2 ) 2 -PPh 2 ) results in formation of the novel compound [Au6(C2C13H11O)4(dppe)2]2+ (1) in good yield, which was isolated as nearly colorless crystals (Scheme 1). The Scheme 1. Synthesis of Complexes 1−8a

a

Reaction conditions: acetone/dichloromethane mixture, 1−12 h, 298 K, yields 78−91%.

assembly of the hexanuclear cluster occurs irrespective of reaction mixture stoichiometry, as a variation of the starting reagent ratio does not give any other isolable products. Using the same approach and other diphosphines with flexible backbones, namely, PCy2-(CH2)2-PCy2, PPh2-(CH2)n-PPh2 (n = 3, 4), 1,2-(PPh2-O)-C6H4, and (R,R)-DIOP, we obtained a family of complexes 2−8 adopting similar arrangements of the metal framework (Scheme 1). It should be noted that we also have made attempts to use the related diphosphine with the smallest bite angle, PPh2-CH2PPh2, in this synthetic route. However, no cluster assemblies could be obtained from the reaction mixture. 2364

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Figure 2. Molecular views of complexes 1, 3, and 7. Counterions and hydrogen atoms are omitted for clarity. Average Au−Au interatomic distances (Å) in 1, 3, and 7 are 3.2894, 3.2602, and 3.2296 (3.2502) Å, respectively (two values for 7 correspond to the independent molecules found in the unit cell).

Figure 3. VT 1H and 31P{1H} NMR spectra of 3 (left), 1H−1H COSY NMR (aromatic region) spectrum of 3 in acetone-d6 at 243 K (middle), and a schematic representation of the nonequivalent phenyl rings in the molecule (o, ortho; m, meta; p, para), (right). The assignment of the signals to the phenyl rings of a given ligand (alkynyl or diphosphine) is arbitrary.

appearance of one singlet in the low-temperature limiting 31P NMR spectrum (see Figure 3 and the Experimental Section), in addition to the septuplet of the PF6− counterion. However, the phenyl rings bound to the same phosphorus atoms are not equivalent in this symmetry group and the proton spectra of these complexes display two sets of the “ortho−meta−para” resonances with typical multiplicity and characteristic {P−H} and {H−H} coupling constants. The 1H−1H COSY and VT 31 P spectra of compound 3 (Figure 3) clearly exemplify the spectroscopic patterns described above. In addition to two sets of the PPh2 signals, the spectrum displays the hydroxyl proton singlet and two sets of the phenyl resonances of the “Ph2(OH)C” substituents at the alkynyl ligands. The duplication of the alkyne phenyl ring signals is determined by the formation of intramolecular O−H···O hydrogen bonds between the hydroxyl groups, which makes the structure rigid and differentiates the position of the Ph moieties. Broadened multiplets of the diphosphine trimethylene bridge appear in the high-field part of the spectrum in the 1.7−3.6 ppm range. It has to be mentioned that despite the fact that the clusters 4−8 tend to dissociate in solution, they effectively and reproducibly assemble upon crystallization into their hexanuclear forms.

display chemical equilibria between the major form and one (for 3 and 5) or a few minor species. The VT 31P NMR spectra (Figure 3 and Figures S4−S16 (Supporting Information)) show that the major form dominates at low temperatures and becomes the only detectable species for 1 and 3−7. The chemical shifts of the minor species are not very different from those of the major species, the result of which is indicative of phosphine ligand coordination in the molecules formed upon temperature growth. This type of behavior is compatible with the dissociative process directly detected by mass spectroscopic measurements (see above). The presence of a few signals in the high-temperature 31P NMR spectra of 1 also suggests simultaneous formation of another species, the characterization of which proved to be impossible. Complex 8 exhibits complicated dynamic behavior even at low temperature (Figure S16), which might involve the presence of several isomers together with dissociated forms, thus preventing reliable spectroscopic investigation of this cluster in solution. At the low -temperature limit all of these clusters show spectroscopic patterns which are completely compatible with the structural motif found for 1−3 and 7 in the solid state. The molecular structure of these complexes belongs to the D2 symmetry group, which makes all phosphorus atoms and alkynyl ligands equivalent. The symmetry results in the 2365

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systematically longer than those observed in the related (AuC2fluorenolyl)10 parent structure (2.8804(5)−3.0937(5) Å).10b On the other hand, the Au−Au contacts in 9 are very close to the corresponding values found in the clusters 1−3 and 7 (see above). The mass spectroscopic and NMR data obtained for 9 are compatible with the stoichiometry and structure found in the solid state. The ESI-MS displays one signal of the doubly charged cation at m/z 1835.3 that completely fits the stoichiometry of the complex. The 1H and 31P NMR measurements show that 9 is stereochemically rigid at room temperature, similar to the case for its structural analogue.10a In compliance with the C2 symmetry of the molecule the 31P NMR spectrum shows two sharp doublets of equal intensity at 37.4 and 32.7 ppm (J(P−P) = 2.1 Hz) in addition to the signal of the counterion. The relatively low symmetry of the cluster 9 structure results in a rather complicated but well-resolved proton spectrum of this compound (Figure S18 (Supporting Information)). In the low-field part of the spectrum one can observe four clearly visible sets of (ortho−meta−para) signals of the phosphine phenyl rings. Three singlets corresponding to the protons of the alkynyl hydroxyl groups confirm the presence of three types of inequivalent alkynyl ligands, each of which bears two inequivalent phenyl rings. The observation of six sets of alkynyl phenyl rings, together with the signals of the phosphorus-bound aromatics, clearly indicates that the solidstate structure is retained in solution. Photophysical Results. The above NMR studies have indicated that, except for the compounds 2 and 9, the rest of the title Au6 clusters are relatively unstable in solution and hence undergo isomerization or perhaps even dissociation, to give multicomponent mixtures. Accordingly, photophysical results in solution could not have a rational correlation with respect to the structure (from X-ray analysis). Therefore, only complexes 2 and 9 have been investigated in solution, while the photophysics of the other complexes were only studied in the solid state due to their well-defined crystal structure (vide supra). As shown in Figure S19 (Supporting Information), an absorption spectrum of 2 in CH2Cl2 reveals a diffuse, structureless band with a shoulder around 275−285 nm. The absorption onset of ∼360 nm is consistent with the calculated value of 357 nm (see Table 2). On the basis of the frontier orbital analysis of the excited state characteristics (Figure S21 (Supporting Information)), the lowest lying electronic absorption can be assigned to a combination of the intraligand π → π* transition of π-conjugated π CC−Au and Au to alkyne metal-to-ligand charge transfer (MLCT). Compound 2 exhibits a rather weak emission maximized at 504 nm (Figure S19), which also matches well the theoretical prediction of 483 nm (Table 2). Note that all spectral and dynamic properties of 2A and 2B in CH2Cl2 are indistinguishable (see Figure S19), as these are two different crystalline modifications of one compound, as evidenced by the NMR data set for 2 in solution. In comparison, the crystals of 2A and 2B represent two forms, found in P21/n and P21 space groups, respectively, which are expected to show different packing morphologies and hence photophysical behavior. Indeed, one can observe a sharp contrast between solid state samples of 2A and 2B which exhibit intense yellow and sky blue emission, maximized at 572 and 482 nm, respectively (see Figure 5 and Table 1). The emission quantum yield is measured to be nearly 1.0 for 2A and 0.76 for 2B. Their phosphorescence characteristics can be

Interestingly, in the case of PPh2-(CH2)4-PPh2 diphosphine and the −C2C(OH)Ph2 alkynyl ligand, only the octanuclear cluster [Au8(C2C13H11O)6(PPh2C4H8PPh2)2]2+ (9) is formed irrespective of the reaction stoichiometry (Scheme 2). A singleScheme 2. Synthesis of Complex 9a

a

Reaction conditions: acetone/dichloromethane mixture, 12 h, 298 K, yield 92%.

crystal X-ray diffraction study revealed the structure shown in Figure 4 (see Figure S2 (Supporting Information) for an

Figure 4. Molecular view of complex 9. Color scheme: yellow, gold; red, phosphorus; green, oxygen. One of the two independent molecules found in the unit cell is shown. Selected interatomic distances (Å): P(1)−Au(1) 2.289(3), P(2)−Au(2) 2.273(3), P(3)− Au(3) 2.268(3), P(4)−Au(4) 2.255(3), Au(1)−Au(5) 3.0840(6), Au(2)−Au(5) 3.2423(6), Au(2)−Au(7) 3.3037(5), Au(3)−Au(7) 3.0155(6), Au(4)−Au(7) 3.2183(6), Au(4)−Au(5) 3.3516(6), Au(5)−Au(7) 3.0934(6), Au(5)−Au(8) 3.1531(5).

ORTEP view). The arrangement of the metal core in 9 is analogous to that found earlier for the [Au8(C2But)6(PPh2C2PPh2)2]2+ complex with the diphosphine having a short −CC− spacer.10a The metal framework of 9 is derived from the parent decanuclear complex (AuC2C(OH)Ph2R)10, in which the gold ions form two interlocked pentagons nearly perpendicular to each other.10b In 9 coordination of the diphosphines results in removal of two Au atoms and decrease of the cluster nuclearity from Au10 to Au8. However, this transformation occurred without destruction of the general structural motif and complex 9 consists of two fused planar fragments [Au4(PPh2C4H8PPh2)]+, linked by the Au−Au bonds and π coordination of the alkynyl ligands to the gold ions. The Au− Au bond distances in 9 (3.0155(6)−3.3637(6) Å) are 2366

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Figure 5. Solid-state emission spectra of complexes 2A, 2B, and 9 at room temperature: λex 380 nm for 2A and 2B and λex 420 nm for 9.

Figure 6. Solid-state normalized emission spectra of complexes 1 and 3−8 at room temperature.

Table 1. Solid-State Photophysical Properties of Complexes 1−9 λem/nm

Φem

1

490

1.00

2A 2B 3 4 5 6 7 8 9 9d

572 482 496 485 485 498 485 502 556 586

1.00 0.76 0.75 1.00 0.73 0.90 0.90 0.61 0.72 0.18

τobsd/μsa b

2.05 3.01c 6.28 5.30 1.43 1.30 1.36 1.14 1.94 2.22 2.42 2.37

kr/s−1 4.88 3.32 1.59 3.85 5.24 7.35 5.36 7.90 3.09 3.72 3.24 7.59

× × × × × × × × × × × ×

different population decay times were obtained: 2.05 and 3.01 μs, respectively. A similar shoulder, though not clearly resolved, also seems to appear in complex 3. This may imply the presence of two packing morphologies or fluctuation between two different cluster arrangements, the rate of which may not be distinguished in the structural analysis but is somewhat slower than the emission decay rate. Nevertheless, the actual mechanism, which is not the focus of this study, is pending resolution. Second, as for the rest of the Au6 complexes, despite the differences in anchoring peripheral R groups as well as the variation in phosphine backbones, their emission spectral features seem to be similar, indicating that the emission originates mainly from the Au and π*(CC) orbitals and is affected by the topology of the Au cluster core. The latter is demonstrated by the red-shifted emission of Au8 cluster 9 (Figure 5, cf. complexes 1−8 except 2A), which has a different geometry of the metal core and network of metallophilic interactions. As mentioned earlier, complex 9 is stereochemically rigid and retains its structure in solution, according to NMR measurements. This observation is further supported by the intense emission of 9 maximized at ∼586 nm in acetone (see Figure S20 (Supporting Information) and Table 1). The observed lifetime (2.37 μs) and quantum yield (0.18) are both on the same order of magnitude as those (2.42 μs and 0.72) in the solid state. In comparison to the 556 nm emission in the solid state, the red-shifted emission peak wavelength in acetone manifests the possible role of solvent reorganization and hence the polarization stabilization in the excited state. Finally, since the R group (see Scheme 1) is optically active, the optical properties of the resulting complexes have been probed. As shown in Figure S21 (Supporting Information), however, complex 8 shows a lack of circular dichroism (CD) CH2Cl2. The result may be rationalized in terms of the R,R ligand configuration combined with a dynamic equilibrium between R and S configurations of the twisted metal−ligand fragment, leading to the disappearance of CD properties. Computational Studies. We carried out quantum chemical calculations with density functional theory (DFT) methods to investigate the structural and photophysical characteristics of the Au(I) clusters 1−9. The geometries of the studied complexes were optimized at the DFT-PBE0 level of theory, after which the lowest energy singlet and triplet excited states were characterized with time-dependent TDDFTPBE0 calculations (see the Experimental Section for full

knr/s−1 5

10 105 105 105 105 105 105 105 105 105 105 104

∼0 ∼0 ∼0 1.22 1.75 ∼0 1.98 8.78 2.06 4.13 1.26 3.46

× 105 × 105 × × × × × ×

105 104 105 104 105 105

a

The excitation wavelength is 380 nm for all title complexes except compound 9 (420 nm). b480 nm. c660 nm. dMeasured in degassed acetone.

verified by long lifetimes of 6.28 and 5.30 μs for 2A and 2B, respectively. The very different luminescence spectra and the associated relaxation dynamics manifest the crucial influence of the intermolecular packing arrangement on the photophysical properties. Interestingly, the irreversible phase transition 2A → 2B can be induced by exposure of the crystalline sample of 2A to the vapors of e.g. acetone or diethyl ether, as indicated by changes in emission color within minutes from yellow to sky blue upon 366 nm UV lamp illumination. Figure 6 shows solid-state emission spectra for compounds 1 and 3−8 at room temperature. These complexes are intensely emissive in the solid state, displaying the quantum yields ranging from 0.61 for 8 to ∼1.0 for 1 and 4. As confirmed by the crystal structure analysis, in the hexanuclear clusters the gold(I) ions coordinate the alkynyl moieties in both σ and π modes. This gives rise to highly effective luminescence, as the T1 state is dominated by contributions arising from the Au and π*(CC) orbitals and the combination of heavy atom enhanced spin−orbit coupling and prominent MLCT character accelerates the S1→ T1 intersystem crossing and likewise enables an efficient T1 → S0 radiative decay pathway. Despite the fact that all complexes exhibit intense emission, certain remarks are worth pointing out. First, in compound 1 in addition to the peak wavelength at 490 nm, there exists a broad shoulder at >550 nm. Upon monitoring at 480 and 660 nm 2367

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computational details). The experimentally observed structural motifs are reproduced in the gas-phase DFT-PBE0 structural optimizations, and the key Au−Au contacts are in good agreement for the cases where X-ray structures are available. The maximum difference in the experimental and theoretical Au(1)−Au(2), Au(3)−Au(4), and Au(5)−Au(6) distances in complexes 1, 2B, 3, and 7 is 0.1 Å. A similar level of agreement was found for complex 9, showing a different topology. The wavelengths predicted for the S0 → S1 and T1 → S0 transitions are given in Table 2, and the electron density Table 2. Computational Photophysical Results for the Au(I) Clusters 1−9 (TDDFT-PBE0) λem(T1 → S0)a λab(S0 → S1) theora,b 1 2 3 4 5 6 7 8 9

361 357 362 358 366 358 340 361 381

(0.01) (0.02) (0.02) (0.01) (0.01) (0.01) (0.01) (0.01) (0.37)

theor

exptl

489 483 517 493 494 497 485 502 507

490 482 (2B) 496 485 485 498 485 502 556

a Wavelengths are given in nm.. bOscillator strengths are given in parentheses.

Figure 7. Electron density difference plots for the lowest energy singlet excitation (S0 → S1) and the lowest energy triplet emission (T1 → S0) of the AuI complexes 1 and 9 (isovalue 0.002 au). During the transition, the electron density increases in the blue areas and decreases in the red areas. Hydrogen atoms and phosphine-based Ph/ Cy rings are omitted for clarity.

difference plots are visualized in Figure 7 for the representative complexes 1 and 9 (complexes 2−8 are illustrated in Figure S22 (Supporting Information)). Complexes 1−8 all show very similar excited-state characteristics. The S0 → S1 excitation and T1 → S0 emission involve both the Au atoms and the alkynyl ligands. The two centermost Au atoms that are σ-bonded to the alkynyl ligands have a clearly larger contribution in comparison to the Au atoms that are π-coordinated to the alkynyl ligands. The structural relaxation of the T1 geometries mainly affects the central metal core, and the Au−Au distances become clearly shorter (for example, the Au(5)−Au(6) distance in complex 1 decreases from 3.11 to 2.78 Å).

form and a few minor forms. In contrast, the higher nuclearity cluster 9 is stereochemically rigid in solution under ambient conditions and retains the structure found in the crystal state. Due to the instability of the molecular forms of most of the compounds in solution the photophysical properties of 1−9 were investigated in the solid state only (except those of 2 and 9). All of these complexes are intensely emissive in the solid at room temperature and demonstrate quantum yields from 0.61 to 1.0. The structurally related hexagold(I) species 1−8 show fairly similar spectral features and display luminescence maxima in a narrow range of energies (485−502 nm) that point to a small electronic contribution of the alkynyl substituents R′ and the diphosphine backbones into the emissive excited states. The cluster 2 was found in two crystalline forms (P21/n and P21 space groups), for which unexpectedly contrasting photoluminescence characteristics were observed. These modifications exhibit yellow and sky blue emissions, maximized at 572 and 482 nm, respectively; these are attributed to the differences in packing morphology and manifest the crucial influence of the intermolecular packing arrangement on the photophysical properties of these types of compounds. The octanuclear cluster 9 has visibly red shifted solid-state emission (556 nm) in comparison to 1−8 and is moderately luminescent in solution as well (quantum yield 0.18), in contrast to the hexanuclear compounds exemplified by the complex 2 (quantum yield ∼5 × 10−4). The experimental studies were supported by DFT calculations, which revealed the origin of electronic transitions responsible for highly effective luminescence. For all of the

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CONCLUSION We have investigated the processes of formation of novel gold(I) alkynyl phosphine aggregates using a family of the diphosphine ligands PR′2-X-PR′2 with variable stereochemistry of the flexible spacer X. Treatment of the decanuclear clusters (AuC 2 R′) 10 with cationic gold diphosphine complexes [Au2(PR′2-X-PR′2)2]2+ allows for the preparation of a family of hexanuclear compounds of general formula [Au6(C2R)4(PR′2-X-PR′2)2]2+ (1−8). These species, stabilized by a range of diphosphines, PPh2-(CH2)n-PPh2 (n = 2 (1), 3 (3−5), 4 (6)), PCy2-(CH2)2-PCy2 (2),1,2-(PPh2-O)-C6H4 (7), and (R,R)-DIOP (8), adopt a similar arrangement of the metal framework that may be considered as consisting of two fused Au4 tetrahedra with a common edge. Interestingly, for the combination of phosphine PPh2-(CH2)4-PPh2 and −C2C(OH)Ph2 alkynyl ligands the octanuclear cluster of a different structural type, [Au8(C2C(OH)Ph2)6(PPh2-(CH2)4-PPh2)2]2+ (9), is formed irrespective of the reaction stoichiometry. The NMR and ESI-MS spectroscopic investigations of complexes 1−8 showed that all but one (2) compounds demonstrate fluxional behavior in solution, which presumably involves dissociative chemical equilibrium between a major 2368

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Calcd for Au6C112H140F12O4P6: C, 42.76; H, 4.49. Found: C, 42.73; H, 4.43. [Au6(C2C13H11O)4(PPh2C3H6PPh2)2](PF6)2 (3). The reaction mixture was stirred for 2 h. Recrystallization by gas-phase diffusion of pentane into an acetone solution of 3 at +5 °C gave pale yellow crystals (91%). ES MS (m/z): [M]2+ 1417.21 (calcd 1417.23). 31P NMR (acetone-d6, 203 K; δ): 13.6 (s, 4P, phosphine), −144.0 (sept, 2P, PF6−). 1H NMR (acetone-d6, 243 K; δ): 8.11 (t, 4H, JHH = 7.7 Hz, para H, phosphine), 7.98 (dd, 8H, JHH = 7.7 Hz, JPH = 12.5 Hz, ortho H, phosphine), 7.73 (d, 8H, JHH = 7.5 Hz, ortho H, alkynyl Ph), 7.72 (dd, 8H, JHH = 7.7 Hz, meta H, phosphine), 7.68 (d, 8H, JHH = 7.2 Hz, ortho H, alkynyl Ph), 7.53 (dd, 8H, JHH = 7.2 Hz, meta H, alkynyl Ph), 7.51 (t, 4H, JHH = 7.2 Hz, para H, phosphine), 7.42 (s, 4H, OH, alkynyl ligand), 7.37 (dd, 8H, JHH = 7.5 Hz, meta H, alkynyl Ph), 7.37 (t, 4H, JHH = 7.2 Hz, para H, alkynyl Ph), 7.26 (m, 8H, JHH = 7.2 Hz, meta H, phosphine), 7.19 (t, 4H, JHH = 7.5 Hz, para H, alkynyl ligand), 7.00 (m, 8H, JHH = 7.2 Hz, JPH = 13.2 Hz, ortho H, phosphine), 3.55− 3.17 (m, 8H, CH2, phosphine), 1.73 (m, 4H, CH2, phosphine). Anal. Calcd for Au6C114H96F12O4P6: C, 43.81; H, 3.10. Found: C, 44.07; H, 3.20. [Au6(C2C6H11O)4(PPh2C3H6PPh2)2](PF6)2 (4). The reaction mixture was stirred for 12 h. Recrystallization by gas-phase diffusion of diethyl ether into an acetonitrile solution of 4 at +5 °C gave pale yellow crystals (78%). ES MS (m/z): [M]+ 1249.22 (calcd 1249.21). 31 P NMR (acetone-d6, 203 K; δ): 31P NMR (acetone-d6, 233 K; δ): 15.2 (s, 4P, phosphine), −144.4 (sept, 2P, PF6−). 1H NMR (acetoned6, 233 K; δ): 8.12 (m, 8H, JHH = 7.7 Hz, JPH = 12.9 Hz, ortho H, phosphine), 7.87 (m, 4H, para H, phosphine), 7.82 (t, 8H, JHH = 7.3 Hz, ortho H, phosphine), 7.72 (t, 4H, JHH = 7.8 Hz, para H, phosphine), 7.63 (dd, 8H, JHH = 7.7 Hz, meta H, phosphine), 7.54 (dd, 8H, JHH = 7.5 Hz, meta H, phosphine), 6.14 (s, 4H, OH, alkynyl ligand), 2.40−2.10 (m, 12H), 1.90−1.58 (m, 28H), 1.46 (m, 8H), 1.24 (m, 4H). Anal. Calcd for Au6C86H96F12O4P6: C, 37.03; H, 3.47. Found: C, 37.03; H, 3.57. [Au6(C2C10H17O)4(PPh2C3H6PPh2)2](PF6)2 (5). The reaction mixture was stirred for 12 h. Recrystallization by gas-phase diffusion of diethyl ether into a dichloromethane solution of 5 at +5 °C gave pale yellow crystals (89%). ES MS (m/z): [M]+ 1357.31 (calcd 1357.31). 31P NMR (acetone-d6, 203 K; δ): 14.2 (s, 4P, phosphine), −144.3 (sept, 2P, PF6−). 1H NMR (acetone-d6, 203 K; δ): 8.09 (dd, 8H, JPH = 13.1 Hz, JHH = 7.8 Hz, ortho H, phosphine), 7.90 (dd, 8H, JPH = 12.5 Hz, JHH = 7.8 Hz, ortho H, phosphine), 7.78 (t, 4H, JHH = 7.7 Hz, para H, phosphine), 7.74 (t, 4H, JHH = 7.7 Hz, para H, phosphine), 7.65 (dd, 8H, JHH = 7.7 Hz, meta H, phosphine), 7.48 (dd, 8H, JHH = 7.8 Hz, meta H, phosphine), 5.56 (s, 4H, OH, alkynyl ligand), 4.10 (m, 4H), 3.47 (m, 4H), 2.54 (m, 4H), 2.11 (8H m), 1.89 (m, 8H), 1.66 (m, 8H), 1.35 (m, 4H), 1.13 (s, 12H, CH3, alkynyl ligand), 0.98 (s, 12H, CH3, alkynyl ligand), 0.89 (s, 12H, CH3, alkynyl ligand). Anal. Calcd for Au6C102H120F12O4P6: C, 40.76; H, 4.02. Found: C, 41.18; H, 4.22. [Au6(C2C6H11O)4(PPh2C4H8PPh2)2](PF6)2 (6). A pale yellow microcrystalline precipitate formed within minutes. The reaction mixture was stirred for 1.5 h and diluted with hexane (10 cm3). The resulting solid was collected by centrifugation, washed with a CH2Cl2/ hexane mixture (1/1 v/v, 3 × 5 cm3), and vacuum-dried to give poorly soluble 6 (81%). ES MS (m/z): [M]+ 1263.24 (calcd 1263.23). The poor solubility and stability in common deuterated solvents did not allow for recording interpretable spectroscopic data. Anal. Calcd for Au6C88H100F12O4P6: C, 37.52; H, 3.58. Found: C, 37.62; H, 3.76. [Au6(C2C13H11O)4(1,2-(PPh2O)2C6H4)2](ClO4)2 (7). The reaction mixture was stirred for 1 h. Recrystallization by gas-phase diffusion of pentane into an acetone solution of 7 at +5 °C gave pale greenish yellow crystals (91%). 31P NMR (acetone-d6, 233 K; δ): 115.5 (s). 1H NMR (acetone-d6, 233 K; δ): 8.30 (t, 4H, JHH = 7.6 Hz, para H, phosphine), 8.21 (m, 8H, ortho H, phosphine), 7.98 (d, 8H, JHH = 7.4 Hz, ortho H, alkynyl ligand), 7.75 (dd, 8H, JHH = 7.8 Hz, meta H, phosphine), 7.64 (dd, 8H, JHH = 7.8 Hz, meta H, alkynyl ligand), 7.62 (d, 8H, JHH = 7.8 Hz, ortho H, alkynyl ligand), 7.41 (t, 4H, JHH = 7.8 Hz, para H, alkynyl ligand), 7.38 (t, 4H, JHH = 7.8 Hz, para H, phosphine), 7.21 (m, 4H, C6H4 phosphine), 7.19 (dd, 8H, JHH = 7.8

compounds, the T1 state is dominated by contributions arising from the Au and π*(CC) orbitals. The heavy atom effect enhances the S1→ T1 intersystem crossing and enables an efficient T1→ S0 radiative decay pathway.

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EXPERIMENTAL SECTION

General Comments. Au(tht)Cl (tht = tetrahydrothiophene)11 and (AuC 2 R) 10 complexes (R = C 6 H 11 O, C 13 H 11 O, (1R)(+)-C10H17)12 were prepared according to the published procedures. [Au2(diphosphine)2]2+ species as PF6− and ClO4− salts were obtained by treatment of a stoichiometric mixture of Au(tht)Cl/diphosphine with AgPF6 or AgClO4, respectively, analogously to the published procedures.13 Tetrahydrofuran was distilled over Na-benzophenone ketyl under a nitrogen atmosphere prior to use. Other reagents and solvents were used as received. The solution 1D 1H and 31P NMR and 1 H−1H COSY spectra were recorded on Bruker 400 MHz Avance and Bruker ACD-HD AV400 and AV600 instruments. Mass spectra were measured on a Bruker micrOTOF 10223 instrument in the ESI+ mode. Microanalyses were carried out at the analytical laboratory of the University of Eastern Finland. 1,2-Bis(diphenylphosphinoxy)benzene. Neat chlorodiphenylphosphine (2.1 g, 9.5 mmol) was added dropwise to a solution of 1,2dihydroxybenzene (0.5 g, 4.5 mmol) and triethylamine (1 g, 9.9 mmol) in tetrahydrofuran (30 cm3) at room temperature over a period of 10 min under a nitrogen atmosphere. The resulting pale suspension was stirred overnight. The precipitate was filtered off, and the solvent was evaporated under vacuum to give a yellow amorphous residue. The product was extracted under nitrogen with hot degassed hexane (3 × 20 cm3) to leave some brown oily material. The volatiles were evaporated to give a nearly colorless moisture- and air-sensitive viscous oil of sufficient (>95%) purity (1.5 g, 71%). 31P{1H} NMR (CDCl3; δ): 113.1 (s). 1H NMR (CDCl3; δ): 7.59 (dd, 3JH,H = 7.5 Hz (av), 8 H, meta Ph), 7.39−7.30 (m, 12 H, ortho and para Ph), 7.14 (m, 2 H, 3-H C6H4), 6.91 (m, 2 H, 4-H C6H4). Synthesis of Complexes 1−8. (AuC2R)10 (0.025 mmol) was dissolved in a 1/2 v/v dichloromethane/acetone mixture (10 cm3), and [Au2(diphosphine)2]2+ as the PF6− or ClO4− salt (0.062 mmol) was added in one portion. The reaction mixture was stirred in the absence of light to give a clear pale yellow solution, which was filtered and evaporated, and the solid residue was recrystallized. [Au6(C2C13H11O)4(PPh2C2H4PPh2)2](PF6)2 (1). The reaction mixture was stirred for 12 h. Recrystallization by gas-phase diffusion of diethyl ether into an acetone solution of 1 at +5 °C gave very pale yellow crystals (84%). ES MS (m/z): [M]2+ 1403.22 (calcd 1403.20). 31 P NMR (acetone-d6, 203 K; δ): 36.0 (s, 4P, phosphine), −144.4 (sept, 2P, PF6−). 1H NMR (acetone-d6, 233 K; δ; major form): 8.13 (m, 8H, ortho H, phosphine), 7.95 (t, 4H, JHH = 7.2 Hz, para H, phosphine), 7.86 (dd, 8H, JHH = 7.2 Hz, meta H, phosphine), 7.63 (d, 8H, JHH = 7.8 Hz, ortho H, alkynyl ligand), 7.44−7.58 (m, 20H), 7.23− 7.35 (m, 16H), 7.18 (m, 8H), 7.14 (t, 8H, JHH = 7.5 Hz), 7.05 (t, 4H, JHH = 7.5 Hz), 3.10 (m, 4H, CH2, phosphine), 2.83 (m, 4H, CH2, phosphine). Anal. Calcd for Au6C112H92F12O4P6: C, 43.43; H, 2.99. Found: C, 43.50; H, 3.19. [Au6(C2C13H11O)4(PCy2C2H4PCy2)2](PF6)2 (2). The reaction mixture was stirred for 12 h. Recrystallization by gas-phase diffusion of diethyl ether into an acetone solution of 2 at room temperature gave pale yellow blocklike crystals of form A (81%). A small amount of nearly colorless crystals of form B was obtained from a dilute solution of 2 under the same conditions. ES MS (m/z): [M]2+ 1427.40 (calcd 1427.38). 31P NMR (acetone-d6, 203 K; δ): 47.1 (s, 4P, phosphine), −144.4 (sept, 2P, PF6−). 1H NMR (acetone-d6, 203 K; δ): 7.80 (d, 8H, JHH = 7.3 Hz, ortho H, alkynyl Ph), 7.69 (d, 8H, JHH = 7.8 Hz, ortho H, alkynyl Ph), 7.43 (t, 8H, JHH = 7.6 Hz, meta H, alkynyl Ph), 7.42 (t, 8H, JHH = 7.7 Hz, meta H, alkynyl Ph), 7.41 (t, 4H, JHH = 7.3 Hz, para H, alkynyl Ph), 7.34 (m, 4H, JHH 7.3 Hz, para H, alkynyl Ph), 7.28 (s, 4H, OH, alkynyl ligand), 2.82 (m, 8H, phosphine), 2.46 (m, 4H, phosphine), 2.18 (m, 8H, phosphine), 2.04 (m, 12H, phosphine), 1.75 (m, 4H, phosphine), 1.71−1.18 (m, 44H, phosphine), 1.04 (m, 8H, phosphine), 0.74 (m, 4H, phosphine), 0.10 (m, 4H, phosphine). Anal. 2369

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Organometallics

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Hz, meta H, alkynyl ligand), 7.06 (t, 4H, JHH = 7.8 Hz, para H, alkynyl ligand), 7.04 (dd, 8H, JHH = 7.8 Hz, meta H, phosphine), 6.78 (m, 4H, C6H4 phosphine), 6.75 (m, 8H, JPH = 13.5 Hz, JHH = 7.8 Hz, ortho H, phosphine). Protons of OH groups of the alkynyl ligands are not observed due to fast exchange with water protons in the solvent. Anal. Calcd for Au6C120H92Cl2O16P4: C, 45.52; H, 2.93. Found: C, 45.85; H, 3.35. [Au6(C2C6H11O)4(R,R-DIOP)2](PF6)2 (8). The reaction mixture was stirred for 12 h. Recrystallization by gas-phase diffusion of diethyl ether into an acetone solution of 8 at +5 °C gave pale greenish yellow crystals (90%). ES MS (m/z): [M]+ 1335.26 (calcd 1335.25). 31P NMR (acetone-d6, 203 K; δ): 16.3 (broad s, 4P, phosphine), −144.2 (sept, 2P, PF6−). 1H NMR (acetone-d6, 233 K; δ; major form): 8.11 (m, 8H, ortho H, phosphine), 7.84 (m, 4H, para H, phosphine), 7.67 (m, 8H, ortho H, phosphine), 7.60 (m, 8H, meta H, phosphine),7.54− 7.45 (12H, AB system of meta H, para H, phosphine), 6.30 (s, OH, 4H, alkynyl ligand), 2.19 (m, 4H), 2.05 (m, 8H), 1.85−1.20 (m, 32H), 1.19−1.03 (m, 4H), 1.02 (s, 12H, CH3, phosphine). The high-field part of the spectrum (3.0−1.0 ppm) was resolved only at 203 K. Anal. Calcd for Au6C94H108F12O8P6: C, 38.12; H, 3.68. Found: C, 38.33; H, 3.86. [Au8(C2C13H11O)6(PPh2C4H8PPh2)2](PF6)2 (9). (AuC2C13H11O)10 (100 mg, 0.025 mmol) was dissolved in dichloromethane (10 cm3), and [Au2(PPh2C4H8PPh2)2](PF6)2 (64 mg, 0.041 mmol) was added in one portion. The reaction mixture was stirred for 12 h in the absence of light to give a clear yellow solution, which was filtered and evaporated. Recrystallization by gas-phase diffusion of diethyl ether into an acetone solution of 9 at +5 °C afforded yellow crystals (92%). ES MS (m/z): [M]2+ 1835.31 (calcd 1835.28). 31P NMR (acetone-d6, room temperature; δ): 37.4 (d, 2P, JPP = 2.1 Hz, phosphine), 32.7 (d, 2P, JPP = 2.1 Hz, phosphine), −144.1 (sept, 2P, PF6−). 1H NMR (acetone-d6, RT; δ): 7.71 (m, 4H, JHH = 7.3 Hz, ortho H, phosphine), 7.68 (m, 4H, JHH = 7.2 Hz, ortho H, phosphine), 7.64 (m, 4H, JHH = 7.4 Hz, JPH = 13.9 Hz, ortho H, phosphine), 7.64 (m, 2H, para H, phosphine), 7.60 (m, 4H, JHH = 7.7 Hz, JPH = 12.9 Hz, ortho H, phosphine), 7.57 (m, 4H, JHH = 7.2 Hz, ortho H, alkynyl ligand), 7.48 (m, 2H, JHH = 7.2 Hz, para H, alkynyl ligand), 7.47 (m, 4H, JHH = 7.7 Hz, meta H, phosphine), 7.43 (d, 4H, JHH = 7.8 Hz, ortho H, alkynyl ligand), 7.43 (d, 4H, JHH = 7.6 Hz, ortho H, alkynyl ligand), 7.38 (m, 2H, JHH = 7.6 Hz, JPH = 13.9 Hz, para H, alkynyl ligand), 7.34 (m, 4H, JHH = 7.6 Hz, meta H, alkynyl ligand), 7.34 (m, 2H, para H, alkynyl ligand), 7.31 (m, 6H, AB2 system of meta H and para H, phosphine), 7.28 (m, 6H, meta H and para H, phosphine), 7.26 (m, 8H, meta H and ortho H, alkynyl ligand), 7.26 (m, 4H, meta H, alkynyl ligand), 7.21 (m, 8H, meta H and ortho H, alkynyl ligand), 7.16 (m, 6H, AB2 system of meta H and para H, phosphine), 7.10 (d, 4H, JHH = 7.8 Hz, ortho H, alkynyl ligand), 7.00 (m, 2H, JHH = 7.8 Hz, para H, alkynyl ligand), 7.00 (m, 2H, JHH = 7.6 Hz, para H, alkynyl ligand), 7.00 (m, 2H, para H, alkynyl ligand), 6.90 (t, 4H, JHH = 7.6 Hz, meta H, alkynyl ligand), 6.72 (s, 2H, OH, alkynyl ligand), 6.52 (t, 4H, JHH = 7.8 Hz, meta H, alkynyl ligand), 5.80 (s, 2H, OH, alkynyl ligand), 5.71 (s, 2H, OH, alkynyl ligand), 2.41 (m, 4H, CH2, phosphine), 2.15 (m, 2H, CH2, phosphine), 1.99 (m, 4H, CH2, phosphine), 1.28 (m, 4H, CH2, phosphine), 0.95 (m, 2H, CH2, phosphine). Anal. Calcd for Au8C146H122F12O6P6: C, 44.26; H, 3.10. Found: C, 44.50; H, 3.49. X-ray Structure Determinations. The crystals of 1−3, 7, and 9 were immersed in cryo-oil, mounted in a nylon loop, and measured at a temperature of 100 K. The X-ray diffraction data were collected on a Bruker Kappa Apex II, Bruker SMART APEX II, or Bruker Kappa Apex II Duo diffractometer using Mo Kα radiation (λ = 0.71073 Å). The APEX214 program package was used for cell refinements and data reductions. The structures were solved by direct methods using the SHELXS-9715 programs with the WinGX16 graphical user interface. A semiempirical absorption correction (SADABS)17 was applied to all data. Structural refinements were carried out using SHELXL-97 and SHELXL-2013.15 Some of the missing solvent molecules in the crystals of 1, 2B, and 9 were omitted, as they were disordered and could not be resolved unambiguously. The missing solvent was taken into account by using a SQUEEZE routine of PLATON.18 The contribution of the solvent to the cell content was not taken into account. In 2A the acetone crystallization molecule was disordered over two sites and

refined with occupancies 0.41/0.59. The aromatic ring C67−C72 in 1 was geometrically idealized. One of the phenyl rings of the acetylene ligand in 2A was disordered over two orientations (C10−C15, C210− C215) and refined with occupancies 0.71/0.29. The diethyl ether solvent molecules in 2A, 9, and some acetone molecules in 2B were partially lost and therefore were refined with the occupation factor 0.5. Some of the PF6− counterions in 1 and 2A were disordered over two positions and were refined with occupancies of 0.78/0.22 and 0.45/ 0.55, respectively. The displacement parameters of the atoms F13− F18 in 1 were restrained so that their Uij components approximate isotropic behavior. The structure 3 was refined as a racemic twin. One of the methanol solvent molecules was disordered over two equivalent positions and was refined with an occupancy of 0.5 at each site. The asymmetric units of 2B, 7, and 9 contain two independent cluster molecules. For each of them in 2B and 7 the disorder models involving counterions and acetone crystallization molecules were found. The phenyl ring (C122−C127) of the alkynyl ligand, PF6− counterion (P11, F13−F18), the cyclohexyl ring of the diphosphine (C173− C178), and crystallization acetone (O12, C234−C236) were disordered over two sites and refined with occupancies 0.64/0.36. Another disorder involves the counterion (P12, F19−F24), the cyclohexyl ring (C85−C90), and crystallization acetone (O14, C240− C242), the components of which were refined with occupation factors 0.59/0.41. In 7 the disordered components of one of the ClO4− counterions (Cl4, O29−31) together with an acetone crystallization molecule (O41, C266−C268) were refined with occupancies 0.50/ 0.50. A series of displacement constraints and restraints were applied to both components of these disorder models. The phenyl ring of the diphosphine (C23−C28) and the acetone molecule (O42, C269− C271) were also disordered and refined with occupation factors 0.51/ 0.49. The disorder models were found as well for the phenyl rings C217−C222 and C223−C228, refined with occupancies 0.50/0.50 and 0.54/0.46, respectively. The idealized positions of the OH hydrogens in 1, 2A, and 3 were estimated with the HYDROGEN19 program and constrained to ride on their parent atom with Uiso = 1.5[U(parent atom)]. The OH hydrogens of O1 and O8 in 2B and O1 in 9 were positioned manually and constrained to ride on their parent atoms. Other hydrogen atoms were positioned geometrically and were constrained to ride on their parent atoms, with C−H = 0.95−0.99 Å and Uiso = 1.2−1.5[Ueq(parent atom)]. The crystallographic details are summarized in Table S1 (Supporting Information). Photophysical Measurements. Steady-state absorption and emission measurements were recorded on a Hitachi (U-3310) spectrophotometer and an Edinburgh (FS920) fluorometer, respectively. The wavelength-dependent excitation and emission response have both been calibrated. Photoluminescence quantum yields (PLQY) in the solid state were determined with a calibrated integrating sphere system incorporated into the fluorometer. The PLQY measurements were conducted in solid microcrystalline samples. The uncertainty of the quantum yield measurement was in the range of ±5% (an average of four replica). Lifetime studies were performed with an Edinburgh FL 900 photon-counting system using a hydrogen-filled lamp as the excitation source. The emission decays were fitted by the sum of exponential functions with a temporal resolution of 300 ps by the deconvolution of the instrument response function. Computational Details. The AuI clusters 1−9 were studied using the hybrid PBE0 density functional.20 The gold atoms were described by a triple-ζ valence quality basis set with polarization functions (def2TZVP).21 Scalar relativistic effects were taken into account by applying a 60-electron relativistic effective core potential for Au.22 A splitvalence basis set with polarization functions on non-hydrogen atoms was used for all the other atoms.23 To facilitate comparisons with experiments, point group symmetry was applied as follows: 1−8, D2; 9, C2.The geometries of all complexes were fully optimized. The excited states were investigated with the time-dependent DFT approach.24 The singlet excitations were determined at the optimized ground-state S0 geometries, while the lowest energy triplet emissions were determined at the optimized T1 geometry. All electronic structure 2370

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(7) (a) He, X.; Yam, V. W.-W. Coord. Chem. Rev. 2011, 255, 2111− 2123. (b) He, X.; Zhu, N.; Yam, V. W.-W. Dalton Trans. 2011, 40, 9703−9710. (c) Lee, T. K.-M.; Zhu, N.; Yam, V. W.-W. J. Am. Chem. Soc. 2010, 132, 17646−17648. (8) Lima, J. C.; Rodriguez, L. Chem. Soc. Rev. 2011, 40, 5442−5456. (9) (a) Mingos, D. M. P.; Yau, J.; Menzer, S.; Williams, D. J. Angew. Chem., Int. Ed. 1995, 34, 1894−1895. (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) Vicente, J.; Gil-Rubio, J.; Barquero, N.; Jones, P. G.; Bautista, D. Organometallics 2008, 27, 646−659. (d) Bruce, M. I.; Jevric, M.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. J. Organomet. Chem. 2010, 695, 1906−1910. (e) Himmelspach, A.; Finze, M.; Raub, S. Angew. Chem., Int. Ed. 2011, 50, 2628−2631. (f) Blanco, M. C.; Camara, J.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Lopez-deLuzuriaga, J. M.; Olmos, M. E.; Villacampa, M. D. Organometallics 2012, 31, 2597−2605. (10) (a) Koshevoy, I. O.; Lin, C.-L.; Karttunen, A. J.; Haukka, M.; Shih, C.-W.; Chou, P.-T.; Tunik, S. P.; Pakkanen, T. A. Chem. Commun. 2011, 47, 5533−5535. (b) Koshevoy, I. O.; Chang, Y.-C.; Karttunen, A. J.; Selivanov, S. I.; Jänis, J.; Haukka, M.; Pakkanen, T. A.; Tunik, S. P.; Chou, P.-T. Inorg. Chem. 2012, 51, 7392−7403. (11) Uson, R.; Laguna, A.; Laguna, M. Inorg. Synth. 1989, 26, 85−91. (12) Koshevoy, I. O.; Lin, C.-L.; Karttunen, A. J.; Jänis, J.; Haukka, M.; Tunik, S. P.; Chou, P.-T.; Pakkanen, T. A. Chem. Eur. J. 2011, 17, 11456−11466. (13) (a) 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. (b) Koshevoy, I. O.; Lin, Y.-C.; Karttunen, A. J.; Haukka, M.; Chou, P.-T.; Tunik, S. P.; Pakkanen, T. A. Chem. Commun. 2009, 2860−2862. (14) APEX2, Software Suite for Crystallographic Programs; Bruker AXS, Madison, WI, USA, 2009. (15) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, A64, 112−122. (16) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838. (17) Sheldrick, G. M. SADABS-2008/1, Bruker AXS Area Detector Scaling and Absorption Correction; Bruker AXS, Madison, WI, USA, 2008. (18) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht University: Utrecht, The Netherlands, 2005. (19) Nardelli, M. J. Appl. Crystallogr. 1999, 32, 563−571. (20) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865−3868. (b) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158−6170. (21) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297−3305. (22) Andrae, D.; Häußermann, U.; Dolg, M.; Stoll, H.; Preuß, H. Theor. Chem. Acc. 1990, 77, 123−141. (23) Schäfer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571−2577. (24) (a) Furche, F.; Rappoport, D., Density Functional Methods for Excited States: Equilibrium Structure and Electronic Spectra. In Computational Photochemistry; Olivucci, M., Ed.; Elsevier: Amsterdam, 2005; pp 93−128. (b) Furche, F.; Ahlrichs, R. J. Chem. Phys. 2002, 117, 7433−7447. (c) van Wüllen, C. J. Comput. Chem. 2011, 32, 1195−1201. (25) Ahlrichs, R.; Bär, M.; Häser, M.; Horn, H.; Kölmel, C. Chem. Phys. Lett. 1989, 162, 165−169.

calculations were carried out with the TURBOMOLE program package (version 6.4).25

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ASSOCIATED CONTENT

S Supporting Information *

Tables, figures, and CIF and xyz files giving X-ray crystallographic data for 1−3, 7, and 9, additional NMR spectroscopic data, and optimized Cartesian coordinates of the studied systems. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for I.O.K.: igor.koshevoy@uef.fi. * E-mail for S.P.T.: [email protected]. *E-mail for P.-T.C.:[email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research has been supported by the strategic funding of the University of Eastern Finland (Russian-Finnish collaborative project and Spearhead project), the Academy of Finland (grant 268993, I.O.K.; grant 138560/2010, A.J.K.), St. Petersburg State University research grant 0.37.169.2014, a grant from the Russian Foundation for Basic Research 14-0300970, and the Bilateral Academic Exchange Program of Ruprecht-Karls-Universität Heidelberg. NMR studies were performed at the Centers for Magnetic Resonance of St. Petersburg State University.

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dx.doi.org/10.1021/om5002952 | Organometallics 2014, 33, 2363−2371