pi-pi 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

摘要

A series of mono- and multinuclear dicyclometalated platinum(II) complexes, namely, [Pt(C<^>N<^>C)L-1] [HC<^>N<^>CH = 2,6-diphenylpyridine; L-1 = 4-tert-butylpyridine (1), 1-methyl-4,4 ' -bipyridinium (MQ(+)) hexafluorophosphate (2(PF6)), 2,6-dimethylphenylisocyanide (4), tricyclohexylphosphine (5), triphenylphosphine (7)], [Pt-2(C<^>N<^>C)(2)(mu -L-2)] [L-2 = pyrazine (pyr; 3), bis(dicyclohexylphosphino)methane (dcpm; 6), bis(diphenylphosphino)methane (dppm; 8)1, and [Pt-3(C<^>N<^>C)(3)(mu (3)-dpmp)] [dpmp = bis(diphenylphosphinomethyl)phenylphosphine (9)], were synthesized from [Pt(C<^>N<^>C)dmso] (dmso = dimethyl sulfoxide). The X-ray crystal structures of 1, 3 . CHCl3 4, 6 . CHCl3. CH3OH . 4H(2)O, 7, 8 (yellow form), and 8 . CHCl3 (orange form) have been determined. For complex 1, the Pt(C<^>N<^>C) units are oriented into pairs in a head-to-tail fashion with an interplanar separation of 3.40 Angstrom. For complex 4, dimeric pi-pi overlap between Pt(C<^>N<^>C) 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(C<^>N<^>C)-phenyl pi-pi interaction (separation 3.381 Angstrom) is apparent in the yellow form. For the orange form (8 . CHCl3), there are two intramolecular Pt(C<^>N<^>C)-phenyl pi-pi contacts (separations 3.115 and 3.287 Angstrom). For 3 . CHCl3, the dihedral angles between the pyrazine and the two Pt(C<^>N<^>C) planes are 124.0 degrees and 130.5 degrees, which allows the possibility for partial orbital interaction between the (5d)Pt and p pi*(pyrazine) orbitals. Complexes 1 and 4-9 display vibronically structured emission (lambda (max) of most intense band = 508-526 nm) in 77 K methanol/ethanol (1:5, v/v) glass, which are assigned to (IL)-I-3 excited states. For 1, 4-6, 8, and 9, the 77 K structureless emission at lambda (max) 596-636 nm in methanol/ethanol glasses is assigned as pi pi* 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 lambda (max) 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 lambda (max) 410 (shoulder) and 456 nm, which are ascribed to the MLCT (5d)Pt --> pi* (1-methyl-4,4 ' -bipyridinium/pyrazine) transition, respectively. Likewise, the solid-state emissions of 2 and 3 at lambda (max) 686 and 658 nm, respectively, are assigned as MLCT. The vapochromism of complex 8 has been investigated. [References: 65]