7218
J. Phys. Chem. 1995, 99, 7218-7226
Luminescent Gold(1) Complexes. Optical and ODMR Studies of Mononuclear Halo(tripheny1phosphine)- and Halo(triphenylarsine)gold(I) Complexes L. J. Larson, E. M. McCauley, B. Weissbart, and D. S. Tinti* Department of Chemistry, University of California, Davis, California 95616 Received: January 6, 1994; In Final Form: May 23, 1994@
Crystals of Ph3PAuX and PhsAsAuX where Ph = phenyl and X = C1 and Br exhibit dual phosphorescences from two excited states. The higher energy system achieves a maximum relative intensity at low temperatures. 0 in all of the complexes, and it is assigned to an intraligand phosphorescence from Its origin is at ~ 3 6 nm a phenyl localized 3nn* state. The zero-field-splitting parameters of the state are ID1 M 0.2 and ]El = 0.04 cm-'. The lower energy system has its origin at w460 nm in all of the complexes and tentative splitting parameters of ID1 0.09 and IEl 0.005 cm-'. The phosphorescence rates of the individual spin levels at 1.4 K range from w5 x lo3 to %lo s-l, with the higher energy system having the larger rates. SCF-XaSW calculations on H3PAuC1, HzPhPAuCl, Ph3PAuC1, PhPH3+, and PhH are also reported for comparison with the experimental results.
Introduction A variety of mono- and multinuclear complexes of Au(1) are luminescent.l-' The luminescences are generally assigned as phosphorescence with the excited state involved derived from a metal-centered or metal-to-ligand charge-transfer excitation. However, the spectra typically do not show resolved vibronic structure, and only the luminescence energies and lifetimes are available to support the assignments. Detailed characterizations of the excited states involved and an understanding of their photophysics are lacking. The present study aims to characterize in detail the lower lying excited states of representative mononuclear Au(1) complexes with arylphosphines and -arsines, as a starting point to later investigate and expose perturbations caused by the metalmetal interactions in homobimetallic complexes of Au(1) with common phosphine and arsine ligands. The complexes chosen for the initial investigation are Ph3PAuX and Ph3AsAuX where Ph = phenyl and X = C1 and Br. Two emission systems are observed for each of these neat complexes. Emission, photoexcitation, absorption, and zero-field optically detected magnetic resonance (ODMR) spectra involving the excited states of these complexes are reported and analyzed for the neat crystalline compounds. The kinetic parameters of the emissive excited states are also reported. SCF-Xa-SW calculations on some model systems are presented for comparison with the experimental results.
Experimental Section Sample Preparation, Ph3PAuX and Ph3AsAuX (X = C1 and Br) were prepared by standard methods8 from reagent-grade materials or obtained from commercial sources. The compounds were purified by multiple recrystallizations using diffusion of ether into solutions of CHzC12. The recrystallized materials were identified and structurally characterized by X-ray diffraction at a 1 3 0 K. All crystals are orthorhombic, space group E12121 with Z = 4. The molecular dimensions obtained at a130 K agree with earlier structure determinations where available? Two structures were found for PhsAsAuCl, as reported elsewhere,1° which differ slightly in the intramolecular orientations of the phenyl groups and in the intermolecularpacking. We will refer @
Abstract published in Advance ACS Abstracts, May 1, 1995.
0022-365419512099-7218$09.0010
to these as needles and prisms, reflecting their predominant external habits. The samples used for spectroscopic study were single crystals (or several small crystallites), selected from the recrystallized materials. Cy3PAuCl (Cy = cyclohexyl) was prepared by reaction of zone-refined PCy3 with (CH3)2SAuCl and recrystallized from ether/CHzClz. Crystals of Cy3PAuCl" are triclinic, space group P i with Z = 2, a = 9.1 16(2) A, b = 10.099(2) A, c = 10.803(3) A, a = 88.62(2)", ,!?= 80.38(2)", and y = 76.74(2)". Et3PAuCl (Et = ethyl) was obtained commercially and used as received. Spectral Studies. Conventional emission spectra were excited with a 100-W Hg or a 75-W Xe lamp together with a 0.25-m monochromator andor solution and glass filters. The spectra were recorded using a l-m Czerny-Turner spectrometer equipped with a cooled RCA C3 1034 photomultiplier tube. Photoexcitation spectra used the l-m spectrometer to detect the emission intensity while scanning the 0.25-m monochromator with a 75- or 450-W Xe lamp. Single-crystal absorption spectra were obtained with the I-m spectrometer and the 75-W Xe lamp. Time-resolved spectra and most decay measurements used a NZ laser (337 nm) for pulsed excitation and, respectively, a boxcar and signal averager for data acquisition. Some decay measurements used a shutter that closed in 1 ms to extinguish the exciting light from a filtered Hg lamp. All reported optical spectra are uncorrected for spectrometer sensitivity or lamp output. In the ODMR studies, the sample was excited with the filtered Hg lamp and the emission intensity detected with the l-m spectrometer. Microwave power was delivered by a rigid coaxial line, terminated with a helical slow-wave structure that surrounded the sample. Slow-passage spectra were obtained by amplitude modulating the microwave power and synchronously detecting the emission intensity. Samples for all of the ODMR studies were at 1.4 K and in zero-applied magnetic field. Raman spectra were excited by the 488-nm Ar+ line and recorded using a Spex Ramalab spectrometer. A HewlettPackard 8450A spectrophotometer was used for solution absorption spectra. Calculations. Standard SCF-Xa-SW calculation^'^^'^ were performed on H3PAuC1, HZPhPAuCl, Ph3PAuC1, PhPH3+, and PhH. The point group symmetries were taken as C3" for H30 1995 American Chemical Society
Luminescent Gold(1) Complexes
J. Phys. Chem., Vol. 99, No. 19, 1995 7219 300 K
1
A
300 K
77 K
7
7
:
4.2 K
~~
350
550
450
Wavelength
/
350
Wavelength
nm
Figure 1. Conventional low-resolution emission spectra of Ph3PAuCl (thin lines) and PhrPAuBr (thick lines) at ambient and low temperatures for excitation at 300 nm. PAuCl and Ph3PAuCl (planes of the phenyl groups in the symmetry planes), C, for H2PhPAuC1 (P-Au-Cl axis in the phenyl plane) and PhPH3+, and D6h for PhH. The bond lengths were P-Au = 2.24, Au-Cl = 2.30, C-P = 1.82, C-C = 1.40, P-H = 1.40, and C-H = 1.10 A. The bond angles were HPH = 95", CPC = 105", and CCC = 120". Other dimensions follow from the assumed symmetries. The bond lengths and angles, which were held constant among the systems studied, are representative of Ph3PAuCl and related comple~es.~-l Atomic exchange parameters were taken from Schwarz.14 A valence-electron-weighted average of the atomic values was used in the interatomic and outer regions. Atomic sphere radii were based on the Norman15 criterion, while the outer-sphere radius was reduced from tangency with the most distant atomic sphere by 0.10 bohr. A Watson16 sphere of negative charge with a radius equal to the outer sphere was used for PhPH3+. The partial wave basis used I,, equal to 4 for the outer shell, 3 for Au, 2 for P and C1, 1 for C, and 0 for H. The SCF calculations were spin restricted, used the quasirelativistic option for Au, and treated the core levels ([Xe]4fL4for Au; [Ne] for P and C1; [He] for C) as single-atom functions. The procedure was converged until the maximum relative change in the potential was
Results Optical Spectra. Figure 1 compares the low-resolution ( x l nm slit width), conventional emission spectra of crystalline Ph3PAuX at 300, 77, and 4.2 K for excitation at -300 nm. Similar results for PhsAsAuX are given in Figure 2. All compounds show two emission systems with origins at about 360 and 460 nm. We refer to these two systems as the HE (high-energy) and LE (low-energy) emissions, respectively. The LE emission of Ph3PAuCl at room temperature shown in Figure 1 agrees well with an earlier report.2 The HE emission, which has not been previously noted, is relatively most intense at any given temperature in Ph3PAuBr. However, it increases in relative intensity with decreasing temperature from 300 to 77 and from 77 to 54.2 K in all of the studied compounds. Among different samples of the same compound, some variability ( ~ 1 0 % is )
450
550
/
nm
Figure 2. Conventional low-resolution emission spectra of PhsAsAuCl (thinlines, with needles above prisms) and Ph3AsAuBr (thick lines) at ambient and low temperatures for excitation at 300 nm.
250
300
Wavelength
350
/
nm
Figure 3. Uncorrected low-resolution photoexcitation spectra of Ph3PAuCl (thin lines) and PhsPAuBr (thick lines) at 1.4 K, monitoring the LE (top) and HE (bottom) emissions. observed in the relative intensities of the HE and LE emissions at 177 K. No emission is observed from neat Cy3PAuC1 or Et3PAuCl under comparable conditions. Low-resolution, uncorrected photoexcitation spectra at 1.4 K are shown in Figures 3 and 4 for the phosphine and arsine complexes, respectively. These show two absorption systems when detecting the HE emission: one has an onset at ~ 3 6 0 nm, which corresponds to the emission origin of the HE system, and the second begins at %280 nm. When detecting the LE emission, an additional strong band at -300 nm is observed. Only very weak, if any, excitation signal is seen between 360 and 460 nm for the LE system. As expected from Figures 3 and 4, the relatjve intensities of the HE and LE emissions at 54.2 K are dependent on the excitation wavelength. The spectra shown in Figures 1 and 2 used excitation wavelengths that roughly maximized the relative intensity of the LE emission.
Larson et al.
7220 J. Phys. Chem., Vol. 99, No. 19, 1995 delay
10
1 o2
1 os
250
300
Wavelength
350 450 550 650
350
/
nm
Wavelength
Figure 4. Uncorrected low-resolution photoexcitation spectra of Ph3AsAuCl (thin lines, with needles above prisms) and Ph3AsAuBr (thick lines) at 1.4 K, monitoring the LE (top) and HE (bottom) emissions. 4
2
2
L
0
I
6
~~
250
300
350
400
Wovelength/nm
Figure 5. Absorption spectra in CHzClz solution at ambient temperature of Ph3PAuX (top panel) and PhsAsAuX (bottom panel) where X = C1 and Br. The absorption spectra of the studied compounds in CHzClz solution at room temperature are given in Figure 5. An intense, structured absorption occurs at 280-260 nm with peak absorptivities of about 2 x lo3 M-’ cm-’. This absorption system, which has been reported in other solvents,17coincides with the highest energy system observed in photoexcitation. A weak absorption occurs in Ph3PAuX between 365 and 300 nm with absorptivities at the maxima of about 2 M-l cm-’. This absorption is not resolved from the tail of the higher energy absorption in Ph3AsAuX. The lower energy system corresponds to the photoexcitation spectra observed in the same wavelength region. No resolved absorption band is seen at ~ 3 0 nm, 0 and no significant absorption is detected in the range 400-800 nm
350 450 550 650
/
nm
Figure 6. Time-resolved low-resolution emission spectra at ambient temperature of Ph3PAuC1 (lhs) and Ph3PAuBr (rhs). for any of the compounds. Hence, the solution absorption spectrum agrees with the photoexcitation spectrum of the HE emission of the crystalline samples but shows no clear evidence of the excitation band(s) of the LE emission. No absorption is seen at 2250 nm in the solution spectrum of Cy3PAuCl. Higher resolution (50.05-nm slit width) emission and absorption spectra were obtained at 1 4 . 2 K for the neat crystals. The vibronic bands of the HE emission resolve into multiple features and/or sharp lines for the phosphine complexes. These are readily interpreted in terms of multiple emissive sites with very similar Franck-Condon envelopes and vibrational frequencies. The relative intensities of the sites vary somewhat among different samples of the same compound, which may account for the small changes seen in the relative intensities of the HE and LE emissions. The vibronic bands of the LE emission in Ph3PAuX and of both the HE and LE emissions in Ph3AsAuX remain relatively broad and/or less resolved at higher resolution and 14.2 K. The absorption spectra of ROS-mm-thick unoriented single crystals show onsets or sharp-line origins at 359.96 nm for Ph3PAuC1, 360.60 nm for Ph3PAuBr, 351.35 nm for Ph3AsAuCl needles, 349.68 nm for Ph3AsAuC1 prisms, and 35 1.86 nm for PhsAsAuBr. These overlap ( f 3 cm-’) the origin of the highest energy feature or zero-phonon line in the HE emission of the corresponding compound at 1.4 K. Hence, the HE system is associated mainly with unperturbed and weakly perturbed (shallow trapped) Ph3PAuX and PhsAsAuX molecules. As evident from comparing Figures l and 2, more strongly pertubed deep traps also contribute to the HE emission in the arsine complexes, especially in the needle form. Figure 6 shows time-resolved emission spectra at room temperature for the phosphine complexes, following pulsed laser excitation at 337 nm. The HE emission dominates the spectra at short times ( 5 1 pus), but only the LE emission is seen at long times ( 2 1 ms). The decay of the HE system appears exponential with a lifetime of 1.7 ps in Ph3PAuC1 and 1.5 ps in Ph3PAuBr. The decay of the LE system is nearly exponential (starting 0.5 ms after excitation) with a lifetime (major component) of 12 and 7.5 ms for Ph3PAuC1 and PhsPAuBr, respectively. The same lifetimes for the LE emission are obtained from the shuttered decay from steady state. The
J. Phys. Chem., Vol. 99, No. 19, 1995 7221
Luminescent Gold(1) Complexes Ph,PAuCl
5.90
(HE)
6.25
Ph,PAuCI
2.83
(LE)
2.88
Ph,PAuBr
6.76
(HE)
6.84
TABLE 1: ODMR Frequencies and Zero-Field-Splitting Parameters for the HE and LE Emissions of Ph3PAuCl and Ph*PAuBr ZFS parameters sitehm frequenciedGHz IDl/cm-* 1Ellcm-I Ph3PAuCl 360.68 360.71 455
6.245 5.910 2.982 2.936
2.702 2.658
360.90 360.95 455
6.778 6.815 2.904
4.591 4.571 2.585
2.120 2.018 0.279 0.279
0.1730 0.1635 0.0948 0.0933
0.0354 0.0337 0.0046 0.0046
0.1896 0.1899 0.0915
0.0365 0.0374 0.0053
PhsPAuBr 2.00
2.15
2.65
Frequency
2.70
2.17
2.25
2.187 2.244
/ Ghz
Figure 7. Zero-field ODMR spectra of the HE and LE emissions of Ph3PAuCl and the HE emission of PhsPAuBr at 1.4 K.
observed lifetime for the LE system of Ph3PAuC1 at ambient temperature disagrees grossly with an earlier report2 of 3 ps (for excitation at 355 nm). However, from Figure 6, we suspect that the earlier report was unduly influenced by spectral overlap at short time with the HE system. In the arsine complexes, only the lifetimes of the LE emission were measured at room temperature, using the shuttered decay from steady state, since laser excitation at 337 nm led to obvious sample coloration. The decays were again nearly exponential and rather long: 30 ms in Ph3AsAuC1 needles, 15 ms in Ph3AsAuCl prisms, and 27 ms in Ph3AsAuBr. Any HE emissions decayed faster than the closing time of the shutter (I 1 ms). The decays of the HE and LE emissions become strongly nonexponential at 5 7 7 K. We assume that this results, at least partly, from complications associated with multiple overlapping sites and, at 1.4 K, from the slowing down of the spin-lattice relaxation rates, as evidenced by the observation of ODMR signals. The analyses of the decays at 1.4 K will be presented after the ODMR results. ODMR Spectra. ODMR signals are observed at 1.4 K when detecting around the origin regions of both the HE and LE emissions. The strongest signals for the HE emission occur near 2 and 6 GHz and yield increases in the emission intensity at resonance. Several signals are seen around each frequency. These were associated with different trap sites from their dependence on the detection wavelength. Example slowpassage ODMR spectra are shown in Figure 7 for the HE emission of Ph3PAuC1 and Ph3PAuBr. The (stronger) signals correspond to two sites whose HE origins are at 360.68 and 360.71 nm (-60-cm-' trap depths) in Ph3PAuCl and at 360.90 and 360.95 nm (e20-cm-' trap depths) in Ph3PAuBr. No signals were seen at the sum or difference of the observed signals for either site in Ph3PAuC1, but weak positive signals were observed at the corresponding difference frequencies for the two sites in PhsPAuBr. On the basis of the similarities of the optical and ODMR spectra, we assume that an unobserved third transition also occurs at the difference frequency in Ph3PAuC1. The results then indicate that the HE emissions in both compounds originate from triplet states with very similar zerofield splittings. Table 1 lists the observed frequencies and the deduced zero-field splitting parameters, D and E , for the sites discussed above. The ODMR signals of the HE emissions in the arsine complexes were much broader and much less well defined, not inconsistent with their generally less well-resolved HE spectra and additional overlapping emissive sites. The stronger signals occurred in two ranges, 2.1-3.5 and 5.0-6.8 GHz. These were not assigned to particular sites. However, the results parallel the observations in Ph3PAuC1 and suggest that the zero-field
splittings in the HE excited state are not significantly different between the phosphine and arsine complexes. The cleanest ODMR results for detection of the LE emission occur in Ph3PAuC1, as expected from the optical spectra. The strongest of these signals, which are included in Figure 7, are a pair of doublets near 2.6 and 2.9 GHz. Additional, weaker signals are seen in Ph3PAuCl over a wide frequency range below 4 GHz, some of which could be possibly associated with splittings engendered by the quadrupolar 35,37C1 and 19'Au nuclei. One of these occurs at 0.28 GHz, which agrees with the common frequency difference between the two strong and the two weak members of the doublets shown in Figure 7. The weak, relatively broad, 0.28-GHz signal is the only observed signal with a negative sign. No signals are observed at the sum frequencies of the members of the doublets. We tentatively assign the noted frequencies in Ph3PAuC1 to the electron-spin transitions of similar triplet states at two sites. This is based on a weak dependence of the relative intensities of the members of the doublets on the detection wavelength around the origin region of the LE emission, which suggests that the more intense members are associated with a slightly higher energy site. The observed frequencies then yield ID1 = 0.0933 and 0.0948 cm-' with a common IE( = 0.0046 cm-'. Signals around 2.6 and 2.9 GHz were also associated with the LE emission of Ph3PAuBr, giving very similar fine structure parameters for similar assumptions. Table 1 includes the discussed frequencies and splitting parameters for the LE triplet state of Ph3PAuCl and Ph3PAuBr. For the LE emission of the arsine complexes, the ODMR signals were again broader and more complicated. The stronger signals occurred in the frequency range 2.9-3.4 GHz, in roughly the same range as the stronger signals in the phosphine complexes. Vibronic Analyses. Low-resolution am-PMDR18 action spectra of the HE emission of Ph3PAuCl and PhsPAuBr, obtained while modulating the ODMR resonances of a particular site, are compared with the corresponding conventional emission spectrum in Figure 8. The am-PMDR spectra have narrower bandwidths even at low resolution, reflecting the selection of a single trap site. However, very similar vibronic features with very similar relative intensities are seen in the am-PMDR and conventional spectra. Also, all of the vibronic bands have the same sign in the am-PMDR spectra. High-resolution am-PMDR spectra were recorded for both Ph3PAuCl and Ph3PAuBr in order to obtain partial, but accurate, analyses of the fundamental vibrations active in the HE emission for a single site. Sharp (55-cm-') zero-phonon lines were obtained for the origins and the more intense vibronic bands within -1600 cm-'. The analyses are summarized in Table 2. The only notable difference at high resolution between the two am-PMDR spectra in a given system occurs near 1600 cm-' from the origin. In both Ph3AuC1 and PhsAuBr, a weak vibronic band is seen at -1576 cm-' when modulating the ODMR
7222 J. Phys. Chem., Vol. 99, No. 19, 1995 Ph3PAuCI
Larson et al.
Ph3PAuBr
Emission
h
Ph,PAuCI
I11
a m 2.936 G H s
n
a m 2.658 G H z
I\
Emission
Emission
,..-.
I
a m 5.910 G H z
am 6.778 G H z
am 2.903 G H z
Ph,PAuBr
360
380
400
Wavelength
380
360
/
400
nm
Figure 8. Comparison of the low-resolution am-PMDR and conventional emission spectra of the HE system of Ph3PAuCI (lhs) and Ph3PAuBr (rhs) at 1.4 K. TABLE 2: Partial Vibronic Analyses of High-Resolution am-PMDR Spectra of PhJPAuCl and PhJPAuBr at 1.4 K IJnm re1 inta v,,Jcm-* Avlcm-I assignmentb Ph3PAuCl (HE)' 360.70 368.90 374.15 374.52 375.68 382.43 382.63
s
w m w
m w ms
360.90 369.13 374.41 374.79 375.92 376.73 377.02 382.70 382.88
s w m w
455.20 458.96 462.79 464.70 466.94 471.72 473.03 477.26 479.65 482.20 483.28 490.99
s w
m
vw w
w ms
mw vw vw
m w,sh
m m
0 616 996 1023 1105 1575 1589 Ph3PAuBr(HE)' 27 701 0 27 083 618 26701 1000 26674 1027 26594 1107 26537 1164 26516 1185 26 123 1578 26 110 1591 Ph3PAuCl (LE)d 21 962 0 21 782 180 21 602 360 21513 449 21410 552 21 193 769 21134 828 20947 1015 20843 1119 20732 1230 20686 1276 20361 1601 27 716 27 100 26 720 26693 26611 26 141 26127
184 (R) 2 x 180 ~AU-P,
449 (W), 450 (IRY 546 (R) or 3 x 180 756 (IR) 360 449 (?) 1024 (R) 1102 (R) or 360 769 449 769 1294 (IR)or 449 828 1585 (R) or 769 828
+
+
mw,sh + m + ms + a s = strong, m = medium, w = weak, v = very, sh = shoulder. bFrequency numbering and descriptions from refs 19 and 20. (R) observed in Raman spectrum at 77 K, (IR) observed in infrared spectrum at 300 K. Measurement accuracy f 0 . 0 2 nm. Measurement accuracy f 0 . 0 5 nm for the stronger features. Weaker features are less accurately known and were measured from conventional emission spectra. e Reference 19. transition at x2 GHz, but this band is absent when modulating the x6-GHz transition. The conventional emission spectra show evidence for a weak band at 1576 cm-'. The deduced frequencies of the active fundamentals are in good agreement ( f 5 cm-') with vibrational frequencies observed in the corresponding Raman spectra of Ph3PAuX at 77 K. All of these fundamentals correspond to m d s s of tAe pi^@ rsaiCcly.@LgyL
450
470
Wavelength
490
/
nm
Figure 9. Comparison of the low-resolution am-PMDR and conventional emission spectra of the LE system of PhsPAuCl (top) and Ph3PAuBr (bottom) at 1.4 K. frequency modes involving motion of the gold or halogen atoms20are not evident. These same fundamentals, discounting the 616-cm-I mode which is too weak to follow, also form progressions,as can be inferred from the lower resolution spectra shown in Figure 8. All but the weak 616-cm-' mode are also seen in the conventional HE spectrum of Ph3PAuC1 at high resolution, based on the highest energy zero-phonon line (which overlaps the absorption origin), with the same frequencies and relative intensities. Low-resolution am-PMDR spectra of the LE emission in Ph3PAuX are shown in Figure 9. These again are very similar to the corresponding conventional emission spectrum. However, the vibronic bands of the LE spectra manifest much less sharpening at high resolution, showing x80-cm-' line widths, than those of the HE spectra. Hence, the vibrational frequencies obtained from analysis of the LE spectra are less certain. Only the results for Ph3PAuC1 are presented in Table 2, based on a combination of the conventional emission and am-PMDR spectra. The 180- and 1600-cm-' modes form clear progressions. The deduced frequencies seem to disagree with the Raman frequencies more than anticipated from the uncertainties.21 Further, several modes are seen that do not occur in the Raman spectrum. The most prominent of these occur at 769 and 1276 cm-'. The IR spectrum of Ph3PAuC1 (recorded in a mineral oil mull at room temperature) does show modes at 756 and 1294 cm-', but these still deviate more than expected. Kinetics. The kinetic parameters of the individual spin levels were deduced for the two studied sites in the HE emission of both Ph3PAuC1 and Ph3PAuBr by standard ODMR methods22 under continuous photoexcitation at 1.4 K. Optical detection was at the corresponding origin so that the deduced relative radiative rates refer explicitly to the origins. The results were obtained with the assumption of negligible spin-lattice relaxation (SLR) at 1.4 K. The spin levels are taken to have the relative order Ty > T, > T,. The varisuS transients showed biexponential recoveries of t h haitahy with rougkdy the sane two rates for both
J. Phys. Chem., Vol. 99, No. 19, 1995 7223
Luminescent Gold(1) Complexes
TABLE 3: Kinetic ParameteM for the HE Emission of Ph3AuCl and Ph3AuBr at 1.4 K sitelnm Ti k~103s-1 k{l% Ph3PAuC1
^ ^
u.u r
T?
0.66 3.2 3.1 0.45 3.1 3.2
TX
T? 360.71
TY TX
Tz
9 52 39 5 54 41
H,PhPAuCI
Ph,PAuCI
G")
(CJ
(Cd
I
~~
360.68
H3PAuCI
0.2
360.95
TV TX
T? T? TI
T2
0.71 3.0 5.0 0.88 2.9 4.8
6 37 57 7 38 55
"Relative order of spin levels taken as Ty > T, > Tz. Total phosphorescence rates k2, &lo%; relative radiative rates k;, f 2 0 % . the T, - T, (2-GHz) and Ty - T, (6-GHz) transitions. Hence, within the signal-to-noise achieved, it was unclear from just these data if the three spin levels were characterized by one short and two similar long lifetimes or two similar short and one long lifetime. The correct assignment of two similar short lifetimes was deduced from the ODMR transients associated with the T, - T, (4-GHz) transition in Ph3PAuBr and extrapolated to Ph3PAuC1. The final results, summarized in Table 3, show that the total depopulation rates, ki, and the relative radiative rates, k f , have similar values in all of the studied traps. Namely, the results give k, x k, x 3 x lo3 s-l, k, 0.7 x lo3 s-l, k,' x k,' I40%, and ky' I10%. The near equality of the rates from T, and T, is consistent with a very weak or absent ODMR signal for the T, - T, transition. The deduced total depopulation rates are in reasonable agreement with the rates observed in the decay of the HE emission of the same sites following pulsed laser excitation at 1.4 K. Good agreement is not expected, since individual sites could not be cleanly resolved optically in the decay measurements. However, the decays were largely a sum of two exponentials, as anticipated from the similarity of kx and k,. These showed components with rates of about 2.8 x lo3 and 0.60 x lo3 s-l in Ph3PAuCl (360.7 nm) and 3.9 x lo3 and ~ 0 . 7x lo3 s-l in PhsPAuBr (360.9 nm) when analyzed as biexponentials for times > 0.1 ms. The decays of the HE emission in Ph3AsAuX at 1.4 K showed components with rates in the same range, (0.2-4) x lo3 s-l. Similar dynamic ODMR studies of the LE emission were limited to the stronger members of the doublets at 2.6 and 2.9 GHz and the weak signal at 0.28 GHz in Ph3PAuCl. Biexponential recoveries of the transients were observed for each of these signals with rates ranging from about 40 to 140 s-l. Again assuming a relative order T, > T, > T, and negligible SLR, the ky' results suggest that k, k, lo2 s-l, k, = 10 s-l, and k,' > k:. However, the data for the relative radiative rates were not internally consistent among the three ODMR transitions, implying that either SLR processes were not negligible at 1.4 K and/or that our assumed assignment of the three ODMR frequencies to the electron spin transitions of a common triplet state is incorrect. However, the problems may be due to the (assumed) coincidence at 0.28 GHz of the T, - T, transition for two sites. We conclude only that the phosphorescence rates of the spin levels for the triplet state of the LE emission in Ph3PAuCl are on the order of 10-lo2 s-l. This agrees with the rates found in the nonexponential decays of the LE emission in Ph3PAuCl and Ph3AsAuX following pulsed laser excitation at 1.4 K.
PhH
(CJ
(Dbh)
,----
-80''
I
-7a"
82"
16"' )I)I
-18a
2" .--We 170,
t
-e10
-70' -6a".,
Ph3PAuBr 360.90
PhPH:
-4Q".' \~
$$'
.I
2e
-lea' =30"
190',, 40"
170'
.--Is:,' -2a
30
' I'
-30"
179 -02"
I,
l&
-160,
-20"
-2e20
Figure 10. Partial energy level diagram in Rydbergs from X a calculations for H3PAuC1, H2PhPAuC1, Ph3PAuCl,PhPH3+, and PhH.
Calculations. The energies from SCF-Xa-SW calculations of the higher energy valence orbitals, which are numbered neglecting the core levels, are summarized in Figure 10 for the ground states of H3PAuC1, H2PhPAuC1, Ph3PAuC1, PhPH3+, and PhH. The results for H3PAuCl and PhH establish the relative ordering of the calculated levels in the other systems. In H3PAuC1, the highest occupied molecular orbital (HOMO) is 5al (Au-s,d), and the lowest unoccupied (LUMO) is 6a1 (Aus,d; C1-s,d). In PhH, the HOMO is elg ( C - p ~ )and , the LUMO is eZu (C-pn*). The HOMO-LUMO gaps are similar in H3PAuCl and PhH, but the energies of both the HOMO and the LUMO are higher in PhH than in H3PAuCl. Accordingly, the calculated HOMO in H2PhPAuC1 and Ph3PAuCl remains largely a phenyl n,while the calculated LUMO is centered mainly on Au, P, and C1. The dashed lines in Figure 10 show in part these major correlations. The symmetries of the phenyl x orbitals correlate elg or eZu (PhH) 2a" (PhPH3+) 2a2 2e (Ph3PAuC1) 2a" (H2PhPAuCl). The Xa-SW method can place the energies of mainly metal orbitals too low relative to ligand orbitals,23and such problems may be a factor in the present results. This becomes especially relevant when estimating the energies and descriptions of the lower-lying excitations in the current systems, since the relative energies of the phenyl-x and Au-centered orbitals have preeminent importance. However, bounds on the conceivable errors are not easily e ~ t i m a t e d . ~The ~ - ~results ~ of the calculations are presented only briefly for comparison with the experimental results and as a possible guide in their interpretation. Table 4 describes the higher-lying filled and lower-lying virtual orbitals for the ground states of H3PAuC1, H2PhPAuC1, Ph3PAuC1, and PhPH3+ in terms of the partitioned charge distributions for contributions 2 5%. The HOMO in the aryl systems is a phenyl-localized n orbital with approximate nodes at C1 (attached to P) and C4. High phenyl character also occurs in the LUMOs of H2PhPAuC1, Ph3PAuC1, and PhPH3+. This appears artificial, however, since the nonpartitioned charges for these orbitals contain unusually large contributions from the intersphere region. Further, the phenyl character in these orbitals would be entirely o-type by symmetry. The phenyl character in e orbitals of Ph3PAuC1 cannot be separated into 0- or Jt-type from just symmetry considerations. The choice is clear for the filled e orbitals by comparison to H2PhPAuC1, but it remains somewhat ambiguous for the virtual e orbitals. The excitation energies obtained from the unrelaxed orbital energies are summarized in Table 5 for the lowest lying transition of each distinct orbital type. Rough descriptions of the excitations, based on the leading terms of Table 4, are included.
-
-
-
+
Larson et al.
7224 J. Phys. Chem., Vol. 99, No. 19, 1995 TABLE 4: Energies and Partitioned Charge Distributions (%) for the Ground-State Orbitals of HJPAuCl, H$hPAuCl, Ph3PAuC1, and PhPH3+ Au orb.
-EIRy*
7a1 5e 6a1 5al 4e 3e 4al 2e
0.036 0.078 0.103 0.497 0.516 0.600 0.625 0.653
lla” loa” 9a” 23a’ Sa” 22a’ 21a’ 7a” 6a“ 20a’ 5a” 19a’
0.063 0.099 0.105 0.107 0.121 0.145 0.172 0.440 0.464 0.574 0.575 0.575
5az 4az 21e 18al 20e 19e 17al 3az 18e 2a2 17e 16e l6a1
0.120 0.135 0.163 0.204 0.229 0.242 0.255 0.515 0.526 0.528 0.556 0.652 0.693
6a” 5a” 15a’ 4a” 3a”
0.118 0.125 0.157 0.458 0.483
s
p
c1
P
s
d
p
d
s
p
TABLE 5: Energies of Various Excitations in HJPAuC1, H2PhPAuC1, PhJPAuCl, and PhPH3+ from Unrelaxed Orbital Energies
Phb d
n
Ph3PAuCl
32 11 7 31 5
7
8 12 6 11 20 9 23 8
100 100 (54) 8
5
8 18 (57) (29)
8
8
60 100 100 100 96
47
11 39
85 10 PhPH3’ 6 19 6 9 13 43
EIeV
5al-6al 5al-5e
H3PAuCl 5.36 5.70
Au-P,Cl CT Au,d-Au,p
7a”-21a’ 7a”- 8a” 20a’-2 1a’ 20a’- Sa“
HzPhPAuCl 3.65 4.34 5.47 6.16
n-Au,P,Cl CT n-n*,P Au,Cl-Au,Cl Au,Cl-n*,P CT
3az-17al 3a2- 20e 16e-17al 16e-20e
Ph3PAuC1 3.54 3.89 5.40 5.75
n-Au,P,Cl CT n-n*,P Au,Cl-Au,Cl,P Au,Cl-n*,P CT
4a”-15a’ 4a”-5a“
PhPH3’ 4.10 4.53
a
H~PAuC~ 25 10 31 26 60 21 6 18 12 6 7 15 26 48 40 6 30 65 100 15 23 48 62 30 HzPhPAuCl 12 83 19 5 6 4 18 9 9 62 5 20 8 13 46 21 10 21 36 10 36 11 12 26 10 10 9 11 12 16 22 100 96 12 25 57 20 76 36 35 23
27
excitation
67 84 42 100 95
1Ry = 13.6 eV = 2.18 x lo-’* J. Orbitals below the gap for each system are filled in the ground state. Entries in parentheses cannot be separated by symmetry into n-or a-type. The n contributions are the sum of the C-p charges; the a contributions and the parenthetical entries are the sum of the C-s, C-p, and H-s charges.
Discussion The experimental results indicate that the HE emission in the studied compounds is intraligand phosphorescence from a state localized on a phenyl moiety of the phosphine or arsine ligand. All of the observations are consistent with this conclusion. The most compelling observations involve the zero-field splittings of the excited state and the vibronic analyses of the major lines from the high-resolution am-PMDR spectra for the shallow trap sites in Ph3PAuX. The magnitudes of the zero-field-splittingparameters are very similar in the HE triplet state of all of the complexes with ID\ % 0.2 and IEl 0.03 cm-’. These values are in the range expected for the lowest 3nn*state of benzene or a substituted benzene with only moderate spin-orbit contributions from a perturbing heavy atom. For example, ID1 0.15 cm-I in benzene27 and chlorinated benzene^,^^,*^ ID1 = 0.2 cm-’ in p-chlorobromobenzene?* and ID1 0.3 cm-’ in p-dibromobenzeneZ8and ~ym-tetrabromobenzene.~~ The magnitude e€ E ia
description“
X-P CT
n-n*
Approximate description based on Table 4.
variable in benzene derivatives, since it depends on the symmetry reduction from D6h wherein E = 0, but generally IEJ I1D)/3. The zero-field ODMR spectra also do not show any obvious splittings due to the quadrupolar halogen or gold nuclei, implying that the spin density on these centers is relatively small. The limited vibronic analyses from high-resolution am-PMDR spectra show that the major active fundamentals in the HE emissions involve motions of the phenyl ring. The phenyl modes also form progressions. Low-frequency modes involving motion of the gold or halogen atom do not contribute significantly. These are the expected results for a 3nn*state that is localized on a phenyl moiety. The mean lifetime of the HE excited state at 1.4 K is significantly shorter in the shallow traps of the complexes (%OS ms) than in benzene (%lo s ) ~ O and is more in accord with brominated benzenes (% 1 ms).28 Hence, spin-orbit interactions involving some heavy atom center must be affecting the triplet state. Based on a 3nn*assignment, the z spin axis is presumed to be perpendicular to the plane of a phenyl moiety with D = -32/2.31 An in-plane spin level, T, or Ty,of a 3nn*state is in general the most active level, while the normal spin level, T,, is typically dark or least a c t i ~ e . ~However, ~ - ~ ~ the experimental results in the complexes imply that the normal spin level is highly radiative (k? = k,‘ >> k;). A z ~ m and i ~ Friedrich ~ et al.?3 in considering external heavy atom effects, have shown that the normal spin level of a 3 n ~ * state can gain radiative strength if a perturbing center is not in the aromatic plane. Ghosh et have also observed such effects in naphthalene attached to crown ether complexes of heavy-metal cations. The P or As atom of the complexes is in the phenyl plane and thus should affect mainly the in-plane spin levels, neglecting any involvement of the P or As d orbitals. However, both intra- and intermolecular gold and halogen atoms are suitably located to enhance the T, activity. The observed similarities in the lifetimes of all of the complexes and the relative atomic numbers argue for perturbation by a Au center. The closest distances in the complexes between a phenyl ring and a Au atom are similar for intra- and intermolecular contacts so that both intemal and external spin-orbit interactions with a Au center could be contributing. In either case, however, T, is expected to gain radiative strength relative to an unperturbed phenyl moiety since the Au is not in the phenyl plane. Although the spin-orbit interactions lead to large changes in the total and radiative phosphorescence rates, other properties of the 3xx* state show that the overall perturbations remain W. In ptwdar, the eeergy of the 3 ~ n state * in the
J. Phys. Chem., Vol. 99, No. 19, 1995 7225
Luminescent Gold(1) Complexes
TABLE 6: Low-Resolution Emission and Excitation Origins (nm)of PhjpAuX and PhAsAuX at T 5 4.2 K HE LE compd” exc. emis. exc. emis. Ph3PAuCl (TI 360.6 361.5 455.4
(9 Ph3PAuBr (TI
(9
284
310b
361.5 285
363.2
350.9 280
352.2
348.5 279
350.0
350.8 283
352.8
455.6
Ph3AsAuC1 (needles) (TI
(9
450.1 297b
PhjAsAuC1 (prisms) (T)
(SI Ph3AsAuBr (TI (SI
448.4 299b 451.0 305b
(T), triplet state; (S), singlet state. Peak maximum.
complexes is very similar to that of halogenated or methylated Accordingly, we assign the absorption and photoexcitation band which onsets at 280 nm in the complexes to the corresponding phenyl-localized l m * state, which occurs in this region in the free ligand.36-38 Table 6 summarizes the low-resolution origins of the HE emission and photoexcitation spectra. The only significant trend is a blue shift by 500-800 cm-’ in the spectra of the arsine complexes relative to the phosphine complexes. Much smaller shifts result from changing the halogen. A similar blue shift also occurs between the solution absorption spectra of Ph3P and P h 3 A ~ . ~However, ~ s ~ ~ in the latter compounds, the vibrational structure normally associated with absorption to the lowest state * is suppressed, and the strength of the transition phenyl * m ~ appears enhanced. This results from the unshared electron pairs (/) on the P and As atoms and the resulting mixing and spectral overlap between the nearby ‘/n* and *mc* state^.^^-^^ The lz* states should be blue shifted in the Au(1) complexes, since the /electrons become more tightly bound. This is supported by the apparent vibrational structure in the solution absorption spectra of the complexes, the molar absorptivities, and the calculations. The crystal structures of the complexes show that the phenyl groups are strongly inequivalent so that intramolecular resonance interactions among the phenyl groups should be unimportant. The experimental results for the HE emission agree with this view. For example, the zero-field parameters are consistent with an excitation that is localized on a single phenyl moiety. Further, the low-energy regions of the photoexcitation and absorption spectra of the crystals are not “mirror images” of the HE emission spectra. Although the origins overlap, other bands in the photoexcitation and absorption spectra show “vibrational” shifts from the respective origins that have no apparent counterparts in the emission spectra. The anomalous shifts also differ among the complexes more than expected for phenyl vibrations. These bands may involve electronic origins associated with alternate phenyl groups. The assignment of the LE emission remains unclear from the experimental data, although the observed lifetimes and ODMR signals indicate a phosphorescent event. The photoexcitation band observed at ~ 3 0 nm 0 is possibly assigned to the singlet state corresponding to the triplet state of the LE emission. Table 6 includes a summary for the LE spectra of the low-resolution origins in emission and peak maxima in excitation. These again show a blue shift in the arsine complexes relative to the phosphine complexes and smaller
shifts between the chloro and bromo complexes. We consider first possible assignments for the LE emission from the calculations. In the related complexes R3PAuX with R = methyl and ethyl, Savas and Mason40 have concluded from spectral data that the HOMO is largely an Au-d orbital and that the lower energy virtual orbitals are mixtures of Au-p and P-n contributions. The X a calculations in H3PAuCl agree with this description but indicate that the halogen also contributes to the virtual orbitals. The calculated lowest excitation energy in H3PAuC1 (5.4 eV) agrees with the onset of the absorption spectra (5.2 eV) in R3PAuC1, reported by Savas and Mason,40 and in Cy3PAuC1, observed herein. The lowest energy excitation from the calculations in the arylphosphine complexes is red-shifted to ~ 3 . 6eV and involves a charge transfer from the phenyl-n HOMO to the LUMO with amplitude on the Au, P, and C1 centers (LMCT). The vibronic analysis of the LE emission in PH3PAuC1 is not inconsistent with an assignment in terms of a 3LMCT (or 3MLCT) state, in that the observed modes include both highfrequency motions that can be associated with a phenyl moiety and low-frequency modes that might involve the heavier atoms. But, the vibrational frequencies appear to disagree with Raman frequencies and with the seemingly corresponding phenyl frequencies from the HE emission. Although this can be ascribed partly to the measurement uncertainties, the disagreement does suggest the LE emission is not associated with a bulk or only weakly perturbed Ph3PAuC1 molecule. Rather, the LE emission appears to arise from a severely perturbed trap or an adventitious impurity$l which is somehow common to all of the studied compounds. An assignment of the HE and LE emissions to different centers would be consistent with their different photoexcitation spectra. Further, thermally nonequilibrated dual phosphorescences from a common center would appear unlikely based on the large energy gap ( ~ 6 0 0 cm-’) 0 between the two triplet states.42 The long lifetime and small zero-field splittings of the LE state also argue against a 3LMCT or 3MLCT assignment that involves orbitals of the Au center. Other conjectures for the LE emission are possible. One possibility, prompted by the long lifetime and small zero-field splittings, involves an association or charge transfer between adjacent phenyl moieties of the phosphine or arsine ligands. This could occur either intermolecularly or intramolecularly, leading to red-shifted 1,3m*-typestates (excimer or CT).43The emission in such cases should be characterized by highfrequency, internal modes of a phenyl group and low-frequency, external motions of the interacting phenyl groups. Such an excited state might also be favored by the perturbed orientations of the interacting phenyl groups at some deep trap site. The temperature dependences of the total emission spectra suggest a thermally activated energy transfer from the HE to the LE excited state, either between two centers or within a common center. At room temperature, this transfer occurs readily, leading to a short lifetime and weak intensity for the HE emission. As the temperature is lowered, the lifetime and relative emission intensity of the HE state increase markedly, reflecting a decreased rate for energy transfer from the HE to the LE state. The lifetime of the LE emission remains surprisingly unchanged between room temperature and low temperatures, indicating that the available channels for depopulation of the LE state are not grossly changing. Summary The compounds Ph3PAuX and Ph3AsAuX exhibit two emission systems. The HE emission at =360 nm, which is assigned to intraligand phosphorescence from a phenyl-localized 3n7c*
Larson et al.
7226 J. Phys. Chem., Vol. 99, No. 19, 199.5 state, is clearly intrinsic to neat Ph3PAuX and PhsAsAuX, based on the agreement of the crystal absorption and highest energy emission origins, of the vibrational frequencies from the emission and Raman spectra, and of the photoexcitation and solution absorption spectra. The bulk of the HE emission intensity originates from slightly perturbed (shallow-trapped) Ph3PAuX and Ph3AsAuX molecules. The corresponding inn* state is seen in absorption and photoexcitation at ~ 2 8 nm. 0 The 9 in fair agreement mean energy of the 1,3nn*states is ~ 3 . eV, with the lowest zn* excitation energy predicted by the X a calculations in Ph3PAuC1. The LE emission at a460 nm also originates from a triplet state. The corresponding singlet state may be due to the photoexcitation band seen at ~ 3 0 nm. 0 The mean energy (E3.4 eV) of these states agrees reasonably with the calculated lowest excitation energy in Ph3PAuC1, which is predicted to involve a LMCT transition. However, the vibronic analysis suggests that LE emission is not associated with only slightly perturbed bulk molecules. Further, the long lifetimes and small zero-field splittings of the LE emission do not endorse either a 3LMCT or a 3MLCT assignment involving a Au center. ODMR studies in a magnetic field of the LE emission in oriented crystals of Ph3PAuC1, which are planned, may clarify its assignment if the structure implied in the zero-field spectra can be interpreted in terms of nuclear quadrupole and hyperfine interactions.
Acknowledgment. We thank Dr. M. M. Olmstead for the X-ray structure determinations and G. K. Mandell and Professor C. P. Nash for assistance in obtaining the Raman spectra. We also thank Professor A. L. Balch and his group for providing some of the complexes and for aid in the synthesis of others. References and Notes (1) Ziolo, R. F.; Lipton, S.; Don, Z. J . Chem. SOC.,Chem. Commun. 1970, 1124. (2) King, C.; Wang, J.-C.; Khan, Md. N. I.; Fackler, J. P., Jr. Inorg. Chem. 1989, 28, 2145. (3) King, C.; Khan, Md. N. I.; Staples, R. J.; Fackler, J. P., Jr. Inorg. Chem. 1992, 31, 3236. (4) Markert, J. T.; Blom, N.; Roper, G.; Perregaux, A. D.; Nagasundaram, N.; Corson, M. R.; Ludi, A,; Nagle, J. K.; Patterson, H. H. Chem. Phys. Lett. 1985,118, 258. Nagasundaram, N.; Roper, G.; Biscoe, J.; Chai, J. W.; Patterson, H. H.; Blom, N.; Ludi, A. Inorg. Chem. 1986, 25, 2947. Lacasce, J. H., Jr.; Tumer, W. A,; Corson, M. R.; Dolan, P. J., Jr.; Nagle, J. K. Chem. Phys. 1987, 118, 289. ( 5 ) Parks, J. E.; Balch, A. L. J . Organomet. Chem. 1974, 71, 453. Balch, A. L.; Doonan, D. J. Organomet. Chem. 1977,131, 137. Balch, A. L.; Catalano, V. J.; Olmstead, M. M. Inorg. Chem. 1990, 29, 585. Balch, A. L.; Fung, E. Y.; Olmstead, M. M. Inorg. Chem. 1990, 29, 3203. (6) Che, C.-M.; Kwong, H.-L.; Yam, V. W.-W.; Cho, K.-C. J. Chem. SOC.,Chem. Commun. 1989, 885. Che, C.-M.; Wong, W.-T.; Lai, T.-F.; Kwong, H.-L. J . Chem. SOC.,Chem. Commun. 1989, 243. Yam, W. V.W.; Lai, T.-F.; Che, C.-M. J. Chem. SOC.,Dalton Trans. 1990, 11, 3747. Che, C.-M.; Yap, H.-K.; Li, D.-M.; Pzng, S.-M.; Lee, G.-S.; Wang, Y.-M.; Liu, S.-T. J. Chem. SOC.,Chem. Commun. 1991, 1615. (7) McClesky, T. M.; Gray, H. B. Inorg. Chem. 1992, 31, 1733. (8) McAuliffe, C. A.; Parish, R. V.; Randall, P. D. J . Chem. SOC., Dalton Trans. 1979, 1730. (9) Baenziger, N. C.; Bennett, W. E.; Soboroff, D. M. Acta Crystallogr. 1976, B32.962. Khan, M.; Oldham, C.; Tuck, D. G. Can. J . Chem. 1981, 59, 27 14. Barron, P. F.; Engelhardt, L. M.; Healy, P. C.; Oddy, J.; White, A. H. A m . J . Chem. 1987,40, 1545. Einstein, F. W. B.; Restivo, R. Acta Crystallogr. 1975, B31, 624. (10) Weissbart, B.; Larson, L. J.; Olmstead, M. M.; Nash, C. P.; Tinti, D. S. inorg. Chem. 1995, 34, 393. (1 1) Larson, L. J.; Olmstead, M. M.; Tinti, D. S. Unpublished results. (12) Johnson, K. H. Adv. Quantum Chem. 1973, 7, 143. Slater, J. C. Quantum Theory of Molecules and Solids; McGraw-Hill: New York, 1974; Vol. 4. Connolly, J. W. D. In Semiempirical Methods of Electronic Structure Calculation, Parr A: Techniques;Segal, G. A,, Ed.; Plenum: New York, 1977; p 105. Case, D. A. Annu. Rev. Phys. Chem. 1982, 33, 151. (13) The program was written by M. Cook and D. A. Case and obtained from QCPE. It was implemented locally on a MicroVAX 3100. (14) Schwarz, K. Phys. Rev. B 1972, 5, 2466; Theor. Chim. Acta 1974, 34, 225. (15) Norman, J. G. Mol. Phys. 1976, 31, 1191.
(16) Watson, R. E. Phys. Rev. 1958, 111, 1108. (17) Gregory, B. J.; Ingold, C. K. J. Chem. Sac. B 1969, 276. Roulet, R.; Lan, N. Q.;Mason, W. R.; Fenske, G. P., Jr. Helv. Chim. Acta 1973, 56, 2405. (18) El-Sayed, M. A.; Owens, D. V.; Tinti, D. S. Chem. Phys. Lett. 1970, 6, 395. (19) Whiffen, D. H. J. Chem. SOC. 1956, 1350. Clark, R. H.; Flint, C D.; Hempleman, A. J. Spectrochim. Acta 1987, 43A, 805. (20) Jones, A. G.; Powell, D. B. Spectrochim. Acta 1974, 30A, 563. Williamson, D. R.; Baird, M. C. J . Inorg. Nucl. Chem. 1972, 34, 3393. (21) The LE emission in Ph3PAuCl shows weak structure on the blue edge of some of the stronger bands. Vibrational frequencies deduced from measurement of these sharper features also do not agree with the Raman frequencies. (22) Shain, A. L.; Shamoff, M. J. Chem. Phys. 1973, 59, 2335. Winscom, C. J.; Maki, A. H. Chem. Phys. Lett. 1971, 12, 264. (23) Case, D. A,; Karplus, M. J. Am. Chem. SOC.1977, 99, 6182. Aizman, A,; Case, D. A. Inorg. Chem. 1981,20, 528. Sontum, S. F.; Case, D. A. J . Phys. Chem. 1982, 86, 1596. (24) Ionization energies were obtained for PhH and H3PAuMe (Me = methyl) from transition-state calculations using the potential of the HOMO and parameters consistent with the other calculations reported herein. Comparison with the experimental values of the lowest ionization energies in PhHzs and (Me3P)AuMeZ6indicates that the calculated values are too small by comparable amounts, 0.96 and 1.2 eV, respectively. These results suggest that the lowest ionization energies in PhH and H3PAuCl also have similar errors so that their relative HOMO energies are not in gross error. This will be moderated by the differences between the HOMOS of H3PAuMe (Au-C bonding orbital) and H3PAuCl (Au-centered nonbonding orbital). Further, the metal character of the HOMO in H3PAuMe is Au-s (20%) and Au-p (21%) with virtually no Au-d contribution, whereas in H3PAuCl the relative contributions of the Au-p and Au-d orbitals are reversed (Table 4). Nevertheless, in HZPhPAuCl and Ph3PAuC1, the phenyl z HOMO is calculated above the highest filled orbital with appreciable Au character by ~ 1 . eV, 8 an amount greater than the implied error in the relative energies. (25) Case, D. A.; Cook, M.; Karplus, M. J. Chem. Phys. 1980,73,3294. Sell, J. A.; Kupperman, A. Chem. Phys. 1978, 33, 367. (26) Bancroft, G. M.; Chan, T.; Puddephatt, R. J.; Tse, J. S. Inorg. Chem. 1982, 21, 2946. (27) de Groot, M. S.; Hesselmann, I. A. M.; van der Waals, J. H. Mol. Phys. 1967, 13, 583. (28) Kothandaraman, G.; Tinti, D. S. Chem. Phys. Lett. 1973, 19, 225. (29) Buckley, M. J.; Harris, C. B.; Panos, R. M. J. Am. Chem. SOC. 1972, 94, 3692. Francis, A. H.; Harris, C. B. J . Chem. Phys. 1972, 57, 1050. (30) Wright, M. R.; Frosch, R. P.; Robinson, G. W. J . Chem. Phys. 1960, 33, 934. (31) Hutchison, C. A., Jr.; Mangum, B. W. J. Chem. Phys. 1961, 34, 908. (32) Azumi, T. Chem. Phys. Lett. 1973, 19, 580. (33) Friedrich, J.; Metz, F.; Don, F. Mol. Phys. 1975, 30, 289. (34) Ghosh, S.; Petrin, M.; Maki,A. H.; Sousa, L. R. J . Chem. Phys. 1987, 87, 4315. (35) McGlynn, S. P.; Azumi, T.; Kinoshita, M. Molecular Spectroscopy of the Triplet State; Prentice-Hall: Englewood Cliffs, NJ, 1969. (36) Jaffe, H. H.; Freedman, L. D. J. Am. Chem. SOC.1952, 74, 1069. Jaff6, H. H. J. Chem. Phys. 1954, 22, 1430. (37) Smirnov, S. G.; Konoplev, G. G.; Rodionov, A. N.; Go&, V. A. Zhur. Prik. Spektros. 1983, 38, 918 [Engl. Transl. J. Appl. Spectros. 1983, 38, 658.1 (38) Fife, D. J.; Morse, K. W.; Moore, W. M. J . Photochem. 1984,24, 249. (39) Kasha, M.; Rawls, H. R. Photochem. Photobiol. 1968, 7, 561. (40) Savas, M. M.; Mason, W. R. Inorg. Chem. 1987, 26, 301. (41) The relative intensities of the HE and LE emissions in Ph3PAuCl are constant for samples recrystallized from solutions containing either no or a slight excess of Ph3P. Hence, incorporated free ligand does not appear responsible for either of the emissions in PhsPAuCl. A large excess of Ph3P yielded the bis complex (Ph3P)zAuCI. However, its spectra indicate similarly that neither emission in Ph3PAuCl is due to incorporation of the bis complex. (42) DeArmond, M. K.; Carlin, C. M. Coord. Chem. Rev. 1981, 36, 325. Kutal, C. Coord. Chem. Rev. 1990, 99, 213. (43) Modiano, S. H.; Dresner, J.; Lim, E. C. J. Phys. Chem. 1991, 95, 9144. Modiano, S. H.; Dresner, J.; Cai, J.; Lim, E. C. J. Phys. Chem. 1993, 97, 3480 and references therein.
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