350045-83-9Relevant academic research and scientific papers
π-π interactions in organometallic systems. Crystal structures and spectroscopic properties of luminescent mono-, bi-, and trinuclear trans-cyclometalated platinum(II) complexes derived from 2,6-diphenylpyridine
Lu, Wei,Chan, Michael C.W.,Cheung, Kung-Kai,Che, Chi-Ming
, p. 2477 - 2486 (2008/10/08)
A series of mono- and multinuclear dicyclometalated platinum(II) complexes, namely, [Pt-(CNC)L1] [HCNCH = 2,6-diphenylpyridine; L1 = 4-tert-butylpyridine (1), 1-methyl-4,4′-bipyridinium (MQ+) hexafluorophosphate (2(PF6)), 2,6-dimethylphenylisocyanide (4), tricyclohexylphosphine (5), triphenylphosphine (7)], [Pt2(CNC)2(μ-L2)] [L2 = pyrazine (pyr; 3), bis(dicyclohexylphosphino)methane (dcpm; 6), bis(diphenylphosphino)methane (dppm; 8)], and [Pt3(CNC)3(μ3-dpmp)] [dpmp = bis(diphenylphosphinomethyl)phenylphosphine (9)], were synthesized from [Pt(CNC)dmso] (dmso = dimethyl sulfoxide). The X-ray crystal structures of 1,3·CHCl3, 4, 6·CHCl3·CH3OH·4H2O, 7, 8 (yellow form), and 8·CHCl3 (orange form) have been determined. For complex 1, the Pt(CNC) units are oriented into pairs in a head-to-tail fashion with an interplanar separation of 3.40 A?. For complex 4, dimeric π-π overlap between Pt(CNC) and phenyl moieties in a head-to-tail manner is observed, with interplanar stacking at 3.39 A?. There are two crystal forms for complex 8. Only one intramolecular Pt(CNC)-phenyl π-π interaction (separation 3.381 A?) is apparent in the yellow form. For the orange form (8·CHCl3), there are two intramolecular Pt(CNC)-phenyl π-π contacts (separations 3.115 and 3.287 A?). For 3·CHCl3, the dihedral angles between the pyrazine and the two Pt(CNC) planes are 124.0° and 130.5°, which allows the possibility for partial orbital interaction between the (5d)Pt and pπ*(pyrazine) orbitals. Complexes 1 and 4-9 display vibronically structured emission (λmax of most intense band = 508-526 nm) in 77 K methanol/ethanol (1:5, v/v) glass, which are assigned to 3IL excited states. For 1, 4-6, 8, and 9, the 77 K structureless emission at λmax 596-636 nm in methanol/ethanol glasses is assigned as ππ* excimeric in nature. These excimeric emissions are concentration-dependent for 1 and 4-6 and concentration-independent for 8 and 9. The 298 K solid emission spectra of 1, 4-6, 8, and 9 are characterized by a broad, unstructured band at λmax 566-633 nm, which red-shift in energy upon cooling to 77 K. These bands are comparable in energy to the 77 K glassy emissions and are similarly assigned. Complexes 2 and 3 show an intense absorption at λmax 410 (shoulder) and 456 nm, which are ascribed to the MLCT (5d)Pt → π*(1-methyl-4,4′-bipyridinium/pyrazine) transition, respectively. Likewise, the solid-state emissions of 2 and 3 at λmax 686 and 658 nm, respectively, are assigned as MLCT. The vapochromism of complex 8 has been investigated.
