Photoluminescence of Tetrameric Copper( I ) Iodide Complexes in Solution

The colorless complexes [Cu(py)I], and [Cu(mor)I], (py = pyridine; mor = morpholine) were shown to be photoluminescent in noncoordinating solvents such as benzene, CH2Cl2, or acetone at room temperature. The red emission (A, = 698 nm) of the pyridine complex in benzene is quite intense (a = 0.04) and decays with a lifetime of T = 0.9 X s. The red photoluminescence (A,, = 654 nm) of the morpholine complex is much weaker (@ = 0.004) and decays with T = 0.3 X 10” s. It is suggested that the emitting state of both complexes is a metal-centered 3d94s1 excited state of Cu(I), but this state is strongly modified by copper-copper interaction in the tetramer which consists of a [CUI], cubane core. During recent years a few Cu(1)-phosphine complexes were shown to be weakly luminescent in solution at room temperature.]J The emitting states were assigned to metal-to-ligand chargetransfer (CT) or perturbed intraligand (IL) excited In addition, a large number of other Cu(1) complexes of the general composition Cu(L)X (L = nitrogen base and X = halogen) were observed to be intensely luminescent a t ambient temperatures, but only in the solid state.The emission behavior of these solid compounds is rather complicated, and its origin does not seem to be very clear. Some of the solid complexes show very large red shifts of the emission when it is compared with the absorption. A typical example is the complex [Cu(py)I], which emits a dual luminescence dependent on its solid-state structure.10 As the tetramer [Cu(py)I],, the colorless compound undergoes a strong yellow emission at room tem~erature.~-’O We report here the observation of the luminescence of [Cu(L)I], with L = pyridine (py) and morpholine (mor) in solution at room temperature. Emission quantum yields and lifetimes were determined. The emission which is quite intense in the case of the pyridine complex is attributed to a copper-centered 3d94s’ excited state which is strongly modified by metal-metal interaction in the tetramers which consist of a [CuII4 cubane core. Experimental Section Materials. The complexes [ C U ( ~ ~ ) I ] , ~ J ~ and [Cu(mor)I],l* were prepared as colorless crystals by the method of Hardt et al. The crystalline materials dissolve rather slowly in weakly coordinating solvents. When precipitated from benzene solution by addition of hexane the complexes are obtained as powders which dissolve more readily. It was suggested that [Cu(py)I], decomposes in benzene, yielding According to our observations, dilute solutions of [Cu(py)I], and [Cu(mor)I], in benzene are stable at room temperature for several hours. Upon standing longer and at higher temperatures the solutions become cloudy due to the precipitation of CUI. Molecular weights of [Cu(py)I], and [Cu(mor)I], were determined by osmometry in solutions of benzene at 37 “C. At this temperature the complexes decomposed slowly. By extrapolation the following molecular weights were obtained: [Cu(py)I], calcd 1078, found 1100; [Cu(mor)I], calcd 11 10, found 1102. (1) (a) Grutsch, P. A.; Kutal, C. J . Am. Chem. SOC. 1977, 99, 6460. (b) Grutsch, P. A.; Kutal, C. Ibid. 1979, 101, 4228. (2) Rader, R. A.; McMillin, D. R.; Buckner, M. T.; Matthews, T. G.; Casadonte, D. J . ; Lengel, R. K.; Wittaker, S. B.; Darmon, L. M.; Lytle, F. E. J . Am. Chem. Soc. 1981, 103, 5906. (3) Buckner, M. T.; Matthews, T. G.; Lytle, F. E.; McMillin, D. R. J. Am. Chem. Soc. 1919, 101, 5846. (4) Fife, D. J.; Moore, W. M.; Morse, K. W. Inorg. Chem. 1984, 23, 1545. (5 ) Segers, D. P.; DeArmond, M. K.; Grutsch, P. A,; Kutal, C. Inorg. (6) De Ahna, H. D.; Hardt, H. D. Z . Anorg. Allg. Chem. 1972, 387, 61. (7) Hardt, H. D.; Pierre, A. Z . Anorg. Allg. Chem. 1973, 402, 107. (8) Hardt, H. D.; Pierre, A. Inorg. Chim. Acta 1977, 25, L59. (9) Hardt, H. D. Naturwissenschaften 1974, 61, 107 and references cited (10) Eitel, E.; Oelkrug, D.; Hiller, W.; Strahle, J . Z . Naturforsch. E: ( 1 1 ) Raston, C. L.; White, A. H. J . Chem. Soc., Dalton Trans. 1976, 2153. (12) Schramm, V.; Fischer, K. F. Naturwissenschaften 1974, 61, 500. Chem. 1984, 23, 2874.