Volume 32 Number 4
I
Inorganic Chemistry
February 17, 1993
0 Copyright 1993 by the American Chemical Society
Communications ~~~
Spectroscopic and Structural hoperties of Binuclear Platinum-Terpyridine Complexes James A. Bailey, Vincent M. Miskowski, and Harry B. Gray' Arthur Amos Noyes Laboratory,?California Institute of Technology, Pasadena, California 91 125 Received August 11. 1992 Square planar d8 complexes show a pronounced tendency to aggregate as weakly metal-metal-bonded oligoners.' The most thoroughly invtstigated materials include infinite-chain Pt(CN)d2speciesz and several luminescent binuclear complexes (e.g., Pt~(PzosH2)4~and [LL'Ir(p-pz)]~(LL' = (C0)2, (CO)(PR3), 1,5-cyclooctadiene;pzH = pyrazole)) that possess metal-metalbonded da*(dz2)pa(pz)excited state^.^ Mononuclear u-diimine complexts of Pt(I1) (e.g., Pt(bpy)(CN)z (bpy = bipyridine)) tend to crystallize as linear chains, and the highly luminescent solid materials are more intensely colored than the monomer^.^ These complextsexhibit luminescencespectra that occur at lower energy and have much different emission profiles than those for the Pt(CN)42-chains. It has been suggested4 that the solid-state emission of this type of complex is attributable to a da* A*(u-diimine) excited state. We have begun an investigation of the photophysics of du*# excited states in discrete binuclear d 8 4 complexes containing polypyridyl ligands. Kostic has characterized { [Pt(tpy)] Z(p-can))(PF& (tpy = terpyridine; can = cana~erine),~ and we have prepared related complexes with a variety of anionic N-N bridging ligands (Table I).6 The colors of the compounds range from light orange (1) to deep red (3, 4). In addition to UV absorptions attributable predominantly t o m * transitions, there are new visible absorption bands that, along with emission maxima, move to lower energy with decreasing Pt-Pt separation (Figure l).' The
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+
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-.
-I
250
I
I
I
I
350
450
550
650
750
1
850
Wavelength (nm)
Figure 1. Electronic spectra of 3 -, absorption at room temperature (CHjCN solution); --, emission at 77 K (1O:lOl Me0H:EtOH:DMF glass); -,excitation at 77 K (1O:lO:l Me0H:EtOH:DMF glass).
--
Contribution No. 8696.
(1) (a) Miller, J. S.,Ed. Exrended Linear Chain Compounds; Plenum
Press: New York, 1982. (b) Keller, H. J.. Ed. Chemistry and Physics o/One Dimensiona~Metals; Plenum Press: New York, 1977. (2) Gliemann, G.; Yersin, H. Struct. Bonding 1985, 62, 87. (3) (a) Roundhill, D.M.; Gray, H. B.; Che, C.-M. Acc. Chem. Res. 1989,
(4)
(5)
(6)
(7)
22,55. (b) Smith, D.C.; Miskowski, V. M.; Mason, W. R.; Gray, H. B. J . Am. Chem. Soc. 1990. 112, 3759. (c) Marshall, J. L.; Hopkins, M. D.; Miskowski, V. M.; Gray, H. B. Inorg. Chem. 1992, 31, 5034. Houlding, V. H.; Miskowski, V. M. Coord. Chem. Reo. 1991, 111, 145 and references therein. Ratilla, E. M. A.; Scott, B. K.; Moxness, M. S.;Kostic, N . M. Inorg. Chem. 1990, 29,918. A related compound ([Pt(tpy)]2(p-guanidine))(C1O4), (5) has been reported: Kip,H.-K.;Che,C.-M.;Zhou, 2.-Y.;Mak,T.C.W.J. Chem. Soc.,Chem. Commun. 1992,1369. The relationship between the Pt-Pt separation (3.090(1), 3.071(1) A) and the absorption spectrum (A,, 483 nm) of 5 accords with our findings. Kip, Che, and co-workers have observed weak emission (4 = 1.27 X lW4) for 5 in fluid CHICN solution. We also have found very weak emissions from 1 4 in CHjCN solutions. (a) Bailey, J. A.; Gray, H. E.Acta Crystallogr. 1992, C48, 1420. (b) Bailey, J. A.; Miskowski, V. M.;Gray, H. B. Acta Crystallogr., in press.
Wavenumber x lo-'
Figure 2. Emission spectra of 1 at 77 K: -, CHlCN solution; --, CH3CN/1% DMF; CH3CN/1% MeOH.
- - -.
solid-state luminescence spectra at ambient temperature for all these complexes exhibit featureless bands (Figure 1) that blueshift slightly at 77 K (Table I); the excited-state lifetimes fall between 1 and 2.5 ps. The 77 K glassy solutions of 2 4 show similar luminescence profiles. Terpyridine vibrations (13001700 cm-I) are enhanced in the resonance Raman spectra of 1-4,
0020-1669/93/1332-0369$04.00/0(8 1993 American Chemical Society
370 Inorganic Chemistry, Vol. 32, No. 4, 1993
Communications
Table I. Structural and SDectroscoDic Data for I P t ( t ~ v l l h ~ - L Complexes l~+ ~~
N-N pc-pyrazole(r-pz) (1)
p-azaindole (p-az) (2)
p-diphenylformamidine (p-dpf') (3)
p-arginine (p-can) (4)
d(Pt-Pt)
(A)
3.432(3)'
3.13(2)/
3.049( 3)l
2.998(2)k
abs A,,
(nm)Ll.b
430 (2520)
460 (2050)
490 (3390)
488 (3700)
emission A,, (nm) 63016308 592h 472,' 5 13' 542,' 585' 69V 6788 639'
lifetime
7
(ps)
Raman Au (cm-t)d 1338 1480
1.lh
410' 497' 2.50'
515'
719 71W 670'
2.51'
730'
