Observation of Low-Energy Metal-Metal-to-Ligand Charge Transfer Absorption and Emission: Electronic Spectroscopy of Cyclometalated Platinum(II) Complexes with Isocyanide Ligands
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- 作者：Siu-Wai Lai ; Hiu-Wah Lam ; Wei Lu ; Kung-Kai Cheung ; and Chi-Ming Che
- 刊名：Organometallics
- 出版年：2002
- 出版时间：January 7, 2002
- 年：2002
- 卷：21
- 期：1
- 页码：226 - 234
- 全文大小：137K
- 年卷期：v.21,no.1(January 7, 2002)
- ISSN：1520-6041
文摘
A series of luminescent mononuclear [(C
NN)Pt(C
NR)]X (HCNN = 6-phenyl-2,2'-bipyridine; R = tBu (1), nBu (2), iPr (3), cyclohexyl (Cy, 4), X = ClO4; R = 2,6-Me2C6H3 (Ar',5), X = PF6) and [(CNN)Pt(CO)]CF3SO3 (6(CF3SO3)) and binuclear [{(CNN)Pt}2(
-CN(CH2)3NC)](PF6)2 (7(PF6)2) complexes were synthesized, and their spectroscopic andphotophysical properties have been investigated. The crystal lattices of 1(ClO4) and 5(PF6)reveal close [CNN] 
- intermolecular contacts (3.4-3.6 Å). Additional metal-metalinteractions are evident in 5(PF6) with intermolecular Pt-Pt distances of 3.3831(9) Å. Atcomplex concentration greater than 5 × 10-3 mol dm-3, the UV-vis absorption spectrum of2 displays a weak shoulder at 511 nm (
= 120 dm3 mol-1 cm-1), which does not obey Beer'slaw. A metal-metal-to-ligand charge transfer (MMLCT) [d
*(Pt-Pt) 
*(CN)] absorptionof a dimeric species via 2[Pt(CNN)(CNnBu)]+ 
[(CNN)Pt(CNnBu)]22+ is proposed.The room-temperature emission spectrum of 4 for complex concentrations 
7 × 10-3 moldm-3 shows a low-energy band at 710 nm originating from a 3MMLCT excited state. Acorresponding well-defined low-energy absorption at 500 nm in the excitation spectrum of4 (
em 710 nm) is assigned to the 1MMLCT transition. The 77 K emissions of complexes 1-6in glassy solutions are sensitive to complex concentration. Upon increasing concentrationsfrom 5 × 10-5 to 2 × 10-3 mol dm-3 for 1-4, red emissions at 600-625 nm ascribed to -excimeric excited states develop at the expense of the vibronic 3MLCT emissions at max~502 nm. Complexes 2 and 4 show additional low-energy emissions at 739 and 710 nm,respectively, attributable to 3MMLCT states. Concentrated 77 K glassy solutions of complexes5-7 exhibit 3MMLCT emissions (max 711-744 nm). The broad structureless solid-stateluminescence of 2(ClO4), 3(ClO4), 5(PF6), 6(CF3SO3), and 7(PF6)2 at 298 K (max 701-748nm) and 77 K (max 744-813 nm) are assigned to 3MMLCT excited states arising fromintermolecular stacking interactions in the solid state. The spectroscopic properties of therelated [(CNC)Pt(L)] (HCNCH = 2,6-diphenylpyridine; L = CO and CNAr') solids arecompared, and no MMLCT emission is evident.
NN)Pt(CNR)]X (HCNN = 6-phenyl-2,2'-bipyridine; R = tBu (1), nBu (2), iPr (3), cyclohexyl (Cy, 4), X = ClO4; R = 2,6-Me2C6H3 (Ar',5), X = PF6) and [(CNN)Pt(CO)]CF3SO3 (6(CF3SO3)) and binuclear [{(CNN)Pt}2(-CN(CH2)3NC)](PF6)2 (7(PF6)2) complexes were synthesized, and their spectroscopic andphotophysical properties have been investigated. The crystal lattices of 1(ClO4) and 5(PF6)reveal close [CNN] - intermolecular contacts (3.4-3.6 Å). Additional metal-metalinteractions are evident in 5(PF6) with intermolecular Pt-Pt distances of 3.3831(9) Å. Atcomplex concentration greater than 5 × 10-3 mol dm-3, the UV-vis absorption spectrum of2 displays a weak shoulder at 511 nm ( = 120 dm3 mol-1 cm-1), which does not obey Beer'slaw. A metal-metal-to-ligand charge transfer (MMLCT) [d*(Pt-Pt) *(CN)] absorptionof a dimeric species via 2[Pt(CNN)(CNnBu)]+ [(CNN)Pt(CNnBu)]22+ is proposed.The room-temperature emission spectrum of 4 for complex concentrations 7 × 10-3 moldm-3 shows a low-energy band at 710 nm originating from a 3MMLCT excited state. Acorresponding well-defined low-energy absorption at 500 nm in the excitation spectrum of4 (em 710 nm) is assigned to the 1MMLCT transition. The 77 K emissions of complexes 1-6in glassy solutions are sensitive to complex concentration. Upon increasing concentrationsfrom 5 × 10-5 to 2 × 10-3 mol dm-3 for 1-4, red emissions at 600-625 nm ascribed to -excimeric excited states develop at the expense of the vibronic 3MLCT emissions at max~502 nm. Complexes 2 and 4 show additional low-energy emissions at 739 and 710 nm,respectively, attributable to 3MMLCT states. Concentrated 77 K glassy solutions of complexes5-7 exhibit 3MMLCT emissions (max 711-744 nm). The broad structureless solid-stateluminescence of 2(ClO4), 3(ClO4), 5(PF6), 6(CF3SO3), and 7(PF6)2 at 298 K (max 701-748nm) and 77 K (max 744-813 nm) are assigned to 3MMLCT excited states arising fromintermolecular stacking interactions in the solid state. The spectroscopic properties of therelated [(CNC)Pt(L)] (HCNCH = 2,6-diphenylpyridine; L = CO and CNAr') solids arecompared, and no MMLCT emission is evident.